1. Which of the following radiations has the highest energy per quantum?
(a) 320-400 nm
(b) 200-280 nm
(c) 280-320 nm
(d) 400-600 nm
[Uttarakhand P.C.S. (Pre) 2012]
Ans. (b) 200-280 nm
- The energy of a photon is related to the wave frequency and wavelength.
- The higher the frequency and the lower the wavelength, the more energy a photon has. 200-280 nm radiation has the highest energy.
- Ultraviolet radiation can be harmful to living cells. It is divided into three sections:
- UV-A (320-400 nm) which causes tanning, UV-B (280-320 nm) which may lead to skin cancer, and UV-C (below 280 nm) which is the most dangerous but absorbed by oxygen in the atmosphere.
|
2. The visible range of solar radiation is-
(a) 100-400 nm
(b) 400-700 nm
(c) 740-10000 nm
(d) None of the above
[53rd to 55th B.P.S.C. (Pre) 2011]
Ans. (b) 400-700 nm
- The electromagnetic spectrum includes all kinds of radiation. Sunlight that reaches Earth is in a range of 100-106 nanometers (nm).
- This range is divided into three parts: infrared (above 700 nm), visible (400-700 nm), and ultraviolet (below 400 nm).
|
3. The wavelength extension of visible light is –
(a) Between 200-900 nm
(b) Between 250-850 nm
(c) Between 300-800 nm
(d) Between 390-780 nm
[U.P.P.C.S.(Mains) 2005]
Ans. (d) Between 390-780 nm
- Visible light is a type of energy that humans can see.
- It usually has wavelengths between 400-700 nanometers (4000-7000Å). Human eyes can typically see something as small as 380 nanometers and as large as 750 nanometers, so option (d) is the correct answer.
|
4. The wavelength of the visible spectrum is in the range :
(a) 1300 Å – 3900 Å
(b) 3900 Å – 7600 Å
(c) 7800 Å – 8200 Å
(d) 8500 Å – 9800 Å
(e) None of the above/More than one of the above
[63rd B.P.S.C. (Pre) 2017]
Ans. (b) 3900 Å – 7600 Å
- Visible light is a type of energy that humans can see.
- It is usually described as having wavelengths between 4,000-7,000 Ångström (400-700 nm).
- This type is between infrared and ultraviolet light.
|
5. The human eye is most sensitive to visible light of the wavelength :
(a) 6050 Å
(b) 5500 Å
(c) 4500 Å
(d) 7500 Å
[U.P.P.S.C. (R.I.) 2014]
Ans. (b) 5500 Å
- Our eyes are most sensitive to yellowish-green light, which has a wavelength of around 555 nanometers.
|
6. Among the colours mentioned below, the eye is most sensitive to colours between :
(a) Red and green
(b) Orange and yellow
(c) Green and blue
(d) Yellow and green
[U.P.P.C.S. (Mains) 2008]
Ans. (d) Yellow and green
- Under normal lighting, our eyes are most sensitive to yellowish-green colors and the wavelength range of 530-570 nanometers.
|
7. Which of the following statements is not correct?
(a) The human ear becomes most sensitive at 1000 Hz.
(b) The human eye becomes most sensitive to red colour.
(c) Persistence of hearing is 1/10 second.
(d) Persistence of vision is 1/16 second.
[U.P. R.O./A.R.O. (Pre) 2021]
Ans. (b) The human eye becomes most sensitive to red colour
- Our ears are most sensitive to sounds between 1000 and 5000 Hz.
- Our eyes are most sensitive to a yellowish-green colour.
- When our eyes are used to the light, they’re able to see light from 400 to 700 nanometers, with the highest sensitivity being at 555 nanometers (yellowish-green).
- The sound we hear stays in our minds for 1/10 of a second. If another sound is heard before that 1/10 of a second is over, our minds mix up the two sounds, and can’t tell them apart.
- Our eyes also keep an image formed on the retina for 1/16 of a second, meaning option b is incorrect.
|
8. The nature of radiation of light is-
(a) Like wave
(b) Like particle
(c) Like both of wave and particle
(d) Like neither of wave nor of particle
[42nd B.P.S.C. (Pre) 1997-98]
Ans. (c) Like both of wave and particle
- At first, it was thought that light was either a wave or a particle.
- But later, it was discovered that it could act as both. This led to the idea that light has a dual nature.
- Quantum mechanics explains this duality by saying that light is like a wave-packet, which can act like either a wave or a particle.
|
9. Light appears to travel in a straight line because –
(a) It consists of small particles.
(b) The velocity of light is very large.
(c) The wavelength of light is very small.
(d) Light is reflected by the surroundings.
[U.P.P.S.C. (R.I.) 2014]
Ans. (c) The wavelength of light is very small
- The wavelength of light is so tiny that it looks like it goes in a straight line.
|
10. Which of the following statements is true?
(a) The light has a greater velocity.
(b) The sound has the greatest velocity.
(c) Celestial objects have the greatest velocity.
(d) Rocket has the greatest velocity.
U.P. Lower Sub. (Pre) 2002
Ans. (a) The light has a greater velocity
- The speed of light in a vacuum is much faster than the speed of sound, which is 0 in a vacuum and 343 m/s in air.
- The speed of light in glass is slower, at 2.0 × 108 m/s. Light always moves faster than sound.
- The speed of things like stars and rockets is much slower than the speed of light.
|
11. The speed of light in a vacuum is near –
(a) 3 × 1010 metre/sec
(b) 3 × 108metre/sec
(c) 3 × 108km/sec
(d) 3 × 108light years
[43rd B.P.S.C. (Pre) 1999]
Ans. (b) 3 × 108metre/sec
- Hence, the speed of light in a vacuum is 3 × 108 m/s.
|
12. The speed of light is –
(a) 9×10² m/sec
(b) 3×1011 m/sec
(c) 3×108 m/sec
(d) 2×104 m/sec
[Jharkhand P.C.S. (Pre) 2003]
Ans. (c) 3×108 m/sec
- The speed of light is measured to have the same value of c = 3×108 m/s no matter who measures it.
|
13. The speed of light in air depends on :
(a) Pressure
(b) Density
(c) It is independent of pressure, temperature and density
(d) Temperature
[Jharkhand P.C.S. (Pre) 2021]
Ans. (*)
- The speed of light changes depending on what kind of material it is travelling through.
- This material’s properties, called optical density, are different from its physical density, which is its mass-to-volume ratio.
- The optical density is measured using something called the refractive index.
- The optical density of air can be affected by the temperature, pressure, and humidity, so the speed of light in air can change because of these factors.
- This can also cause something called atmospheric refraction, like a mirage.
|
14. Velocity of light is maximum in –
(a) Diamond
(b) Water
(c) Vacuum
(d) Hydrogen
[U.P.P.S.C. (R.I.) 2014]
Ans. (c) Vacuum
- Light travels very quickly in empty space (3 × 108 ms–1).
- When it passes through materials like water or glass, the speed of light slows down.
- It moves the slowest in diamond.
|
15. The speed of light will be minimum while passing through–
(a) Glass
(b) Vacuum
(c) Water
(d) Air
[I.A.S. (Pre) 1994]
Ans. (a) Glass
- The material with the highest refractive index (like glass) will allow light to travel the slowest.
- Glass has the highest refractive index compared to other substances like vacuum, water and air.
|
16. The time taken to reach the Sunlight up to the surface of earth is approximately –
(a) 4.2 sec
(b) 4.8 sec
(c) 8.5 minutes
(d) 3.6 hrs.
[42nd B.P.S.C. (Pre) 1997]
Ans. (c) 8.5 minutes
- It takes 8.3 minutes for sunlight to get to the Earth. Therefore, choice (c) is correct.
|
17. Light from the Sun reaches Earth in about :
(a) 2 minutes
(b) 4 minutes
(c) 8 minutes
(d) 16 minutes
[U.P.P.C.S. (Mains) 2006]
Ans. (c) 8 minutes
- It takes the sun’s light approximately 8 minutes and 20 seconds to travel the roughly 150 million km from the sun to the Earth.
- The speed of light is about 300,000 km per second.
|
18. The sunlight from the sun to the earth reaches in :
(a) 5 minutes
(b) 6 minutes
(c) 8 minutes
(d) 10 minutes
(e) None of the above/More than one of the above
[65th B.P.S.C. (Pre) 2019]
Ans. (c) 8 minutes
- It takes 8 and a half minutes for the sun’s light to get to Earth.
- This light moves at a very high speed – 299,792 km/sec (or 186,287 miles/sec).
- The Earth is around 150 million km away from the sun.
|
19. Which of the following has the highest velocity?
(a) Cosmic rays
(b) Light
(c) Electron
(d) Supersonic wave
[U.P. P.C.S. (Pre) 2018]
Ans. (b) Light
- Light is the fastest that anything can travel.
- It can move through empty space, while sound cannot.
- The speed of light is highest in empty space.
- The energy of most cosmic rays is between 100 MeV and 10 GeV, which is almost the same speed as light in a vacuum.
- The highest energy cosmic rays might be slightly slower than light in a vacuum.
|
20. Which of the following does not change when light travels from one medium to another?
(a) Velocity
(b) Wavelength
(c) Frequency
(d) Refractive index
(e) None of the above / More than one of the above
[66th B.P.S.C. (Pre) 2020]
Ans. (c) Frequency
- When light moves from one material to another, its speed, wavelength, and refractive index of the material change, but its frequency remains the same.
|
21. When light waves pass from air to glass the variable affected are –
(a) Wavelength, frequency and velocity
(b) Velocity and frequency
(c) Wavelength and frequency
(d) Wavelength and velocity
[I.A.S. (Pre) 2001]
Ans. (d) Wavelength and velocity
- When light passes from air to glass, its wavelength and speed are changed.
- The light bends, which causes the wavelength to become shorter.
- The speed also becomes slower. However, the frequency of the light does not change.
|
22. When light passes from one medium to another medium, which one of the following does not change :
(a) Intensity
(b) Velocity
(c) Wavelength
(d) Frequency
[U.P.P.C.S. (Mains) 2003]
Ans. (d) Frequency
- When light goes from one substance to another, the rate stays the same.
- The rate is the only thing that stays the same when light moves from one material to another.
|
23. When a ray of light travels from a denser medium to a rarer medium then
(a) It speeds up and bends away from the normal
(b) It speeds up and bends towards the normal
(c) It slows down and bends away from the normal
(d) It slows down and bends towards the normal
[Chattisgarh P.C.S. (Pre) 2018]
Ans. (a) It speeds up and bends away from the normal
- When light moves from a thicker material to a thinner one, it moves faster and bends away from the normal.
- On the other hand, when light moves from a thinner material to a thicker one, it slows down and bends towards the normal in the thicker material.
|
24. The formation of glittering colours in the thin foam of soap is the result of the following phenomenon –
(a) Total refection and interference
(b) Total refraction and dispersion
(c) Diffraction and dispersion
(d) Polarization and interference
[I.A.S. (Pre) 1993]
Ans. (a) Total refection and interference
- When light hits soap bubbles, some of it is reflected back off the outer part of the bubble, and some of it passes through and reflects off the inner part.
- This combination of reflected and refracted light creates a sparkling colour in the thin foam.
|
25. Total internal reflection can take place when light travels from :
(a) Diamond to glass
(b) Water to glass
(c) Air to water
(d) Air to glass
[I.A.S. (Pre) 1996]
Ans. (a) Diamond to glass
- Total internal reflection occurs when light travels from a denser material to a less dense material and the angle of incidence is greater than the critical angle.
- In this situation, the light is completely reflected from the surface. Option (a) is correct because a diamond is denser than glass, which causes total internal reflection.
|
26. A cut diamond shines brilliantly due to
(a) Some inherent property
(b) Total internal refection
(c) Its molecular structure
(d) Absorption of light
[U.P.P.C.S. (Pre) 2017, U.P.P.C.S. (Mains) 2015]
Ans. (b) Total internal refection
- A diamond sparkles because of the way it reflects light inside it.
- Its low critical angle of 24.4 degrees makes it shine brighter than a piece of glass of the same size.
- That’s why diamonds look more brilliant than glass.
|
27. The diamond appears lustrous because of :
(a) Refection
(b) Refraction
(c) Total Internal Reflection
(d) Scattering
[U.P.P.C.S. (Mains) 2012, U.P.P.C.S. (Pre) 1996]
Ans. (c) Total Internal Reflection
- Diamond has a very high refractive index, so its critical angle is also low.
- This allows it to sparkle because when light enters, it bounces off the inside surfaces multiple times, and the colors in the light get split up and become visible.
|
28. What is the reason behind the extraordinary shining of the diamond cuts in a proper way?
(a) Because it has a higher transparency
(b) Because it has a higher refractive index
(c) Because it is so hard
(d) Because it has a fixed deviation for
[I.A.S. (Pre) 1994]
Ans. (b) Because it has a fixed deviation for
- Diamonds sparkle because they are able to reflect a lot of light.
- The refractive index of a diamond determines how much light is bounced back.
- The higher the refractive index, the more light is reflected.
- The diamond is cut to make sure that when light hits it, the light bounces around many times inside the diamond.
|
29. Given below are two statements, one labelled as
Assertion (A) and other labeled as Reason (R) :
Assertion (A): A diamond sparkles more than a glass imitation cut to the same shape.
Reason (R): The refractive index of diamond is less than that of glass.
In the context of the above two statements, which one of the following is correct?
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is not a correct explanation of A
(c) A is true but R is false.
(d) A is false but R is true.
[I.A.S. (Pre) 1995]
Ans. (c) A is true but R is false
- A diamond sparkles more than a glass crystal of the same size and shape because it has a higher refractive index.
- The diamond has a smaller critical angle, which means the light inside it reflects off its inner surfaces multiple times before it leaves.
- Glass has a lower refractive index than diamond, so statement A is correct but reason R is incorrect.
|
30. Optical fibre works on the principle of :
(a) Total internal reflection
(b) Refraction
(c) Scattering
(d) Interference
[U.P. U.D.A./L.D.A. (Pre) 2010, U.P.P.C.S. (Spl) (Pre) 2008, I.A.S. (Pre) 1995]
Ans. (a) Total internal reflection
- Optical fibre is a thin strand of glass or plastic used to transfer light from one place to another.
- It works by completely reflecting the light back so that no signal is lost.
|
31. The phenomenon used in optical fber for transmission of light energy is
(a) Total internal refection
(b) Difraction
(c) Scattering
(d) Refraction
[U.P.P.C.S. (Pre) 2019]
Ans. (a) Total internal refection
- The phenomenon used in optical fiber for transmission of light energy is total internal reflection
|
32. Which one of the following phenomena is used in optical fibres?
(a) Interference
(b) Refraction
(c) Total internal refection
(d) Polarisation
[U.P.P.C.S. (Mains) 2015]
Ans. (c) Total internal refection
- Total internal reflection happens when light moves from a place that is more dense to one that is less dense at a certain angle.
- Optical fibers use this phenomenon, where light enters one end and bounces off the boundary, trapping the light inside the fiber.
|
33. In fiber-optic communication, the signal travels in the form of-
(a) Lightwave
(b) Radio wave
(c) Microwave
(d) Electric wave
[R.A.S./R.T.S.(Pre) 2012]
Ans. (a) Lightwave
- Fiber-optic communication is a way of sending data from one spot to another using light signals that travel through a special fiber.
|
34. Consider the following statements :
1. Fibre optics is based on the principle of total internal refection.
2. In an optical fibre communication system, power consumption is extremely low.
3. Optical fibre communications are free from radio frequency interference.
4. In India, Reliance Group of Industries is engaged in the manufacture of the optical fbre.
Which of these statements are correct :
(a) 1, 2 and 3
(b) 1, 2 and 4
(c) 1, 3 and 4
(d) 2, 3 and 4
[U.P. P.C.S. (Pre) 2003, U.P. U.D.A./L.D.A. (Pre) 2002, U.P. P.C.S. (Pre) 2001]
Ans. (a) 1, 2 and 3
- Optical fibres are thin and flexible cables made of glass or plastic.
- They work by totally reflecting the light inside.
- They don’t need much power and can’t be interfered with by radio waves or electromagnets.
- In 2000, Sterlite-Tech in India started making optical fibre, not Reliance Group. So, option (a) is correct.
|
35. ‘Endoscope’ used by the doctors for examining the inside of patient’s stomach, works on the principle of-
(a) Refection of light
(b) Dispersion of light
(c) Refraction of light
(d) Total internal refection of light
[U.P. Lower Sub. (Pre) 2009]
Ans. (d) Total internal refection of light
- Endoscopes are often used to look inside the body’s hollow organs or cavities.
- They use a bundle of fiber optics which reflects light inside.
|
36. An endoscope is used by a physician to view the internal parts of a body organ. It is based on the principle of –
(a) Refraction of light
(b) Refection of light
(c) Total internal reflection of light
(d) Dispersion of light
[U.P.P.C.S. (Pre) 2010, U.P.P.C.S. (Mains) 2009, U.P.P.C.S. (Spl) (Mains) 2008, I.A.S. (Pre) 1999]
Ans. (c) Total internal reflection of light
- An endoscope is a medical device that uses total internal reflection to view the internal parts of a body organ
|
37. The reason of mirage is
(a) Interference of light
(b) Diffraction of light
(c) Polarization of light
(d) Total internal refection of light
[U.P.P.C.S.(Pre) 2012, U.P.P.C.S. (Pre) 1995]
Ans. (d) Total internal refection of light
- The mirage is caused by light bending when it passes through layers of air with different densities.
- In Deserts, the air gets hotter closer to the ground, which makes each layer of air higher up a bit denser than the one below.
- The light from a distant object, like a tree, gets bent when it moves from a denser to a less dense layer.
- This causes it to bend away from its normal path.
- When the light is at a certain point, it reflects back into the eyes of an observer and looks like an upside-down image of the tree.
|
38. Mirage formation is an example of –
(a) Refraction
(b) Dispersion
(c) Total internal refection
(d) Difraction
[U.P.P.C.S. (Mains) 2014, U.P. U.D.A./L.D.A. (Pre) 2013, U.P. Lower Sub. (Mains) 2013]
Ans. (c) Total internal refection
- The mirage is caused by light being bent when it passes through different layers of air with varying levels of density.
- In the desert, the air gets hotter near the ground, making the air higher up more dense than the air closer to the ground.
- Light from a far away object, such as a tree, is bent when it moves from a denser layer to a less dense layer.
- This causes it to be diverted from its usual path. When the light is in a particular spot, it is reflected back to the eyes of someone looking and appears like a flipped image of the tree.
|
39. Consider the following natural phenomena :
1. Terrestrial heating
2. Refection of light
3. Refraction of light
4. Diffraction of light
Due to which of these phenomena is mirage formed ?
(a) 1 and 2
(b) 2, 3 and 4
(c) 1 and 3
(d) 4 only
[I.A.S. (Pre) 2002]
Ans. (c) 1 and 3
- In deserts, the heat of the air causes different layers to have different densities.
- When a ray of light from a distant object like a tree passes through these layers, it gets bent away from the normal until it hits a layer at an angle greater than the critical angle.
- This causes the light to be reflected back to the observer’s eyes, creating the illusion of an upside-down version of the tree.
|
40. Which one of the following reflects back more sunlight as compared to other three?
(a) Sand Desert
(b) Paddy crop land
(c) Land covered with fresh snow
(d) Prairie land
[U.P. P.C.S. (Pre) 2021]
Ans. (c) Land covered with fresh snow
- Snow-covered ground reflects more sunlight than other surfaces.
- Fresh snow and ice are so reflective that they send back up to 85% of the sunlight that hits them.
- This means that skiers can get sun exposure from all sides due to the light reflecting off the snow.
- Scientists refer to this reflective quality as ‘albedo’, which means whiteness in Latin.
- Snow and ice have the highest albedo of all surfaces.
|
41. The technique to integrate and mark the image of a three-dimensional object is
(a) Audiography
(b) Lexicography
(c) Photography
(d) Holography
[R.A.S./R.T.S. (Pre) 1999, R.A.S./R.T.S. (Pre) 1996]
Ans. (d) Holography
- Holography is a method of creating a three-dimensional image of something.
- It is used with sound, light, or any type of wavelength.
- It is often used to save transcripts and for Microfiche (a big piece of film with tiny pictures from newspapers, catalogs, and more).
- Additionally, it is used to make 3D movies.
|
42. Which of the following is used to take 3-dimensional pictures –
(a) Photography
(b) Holography
(c) Radiography
(d) None of the above
[U.P.P.C.S. (Mains) 2008, U.P.P.C.S. (Pre) 1990]
Ans. (b) Holography
- Holography is a way of creating a 3D representation of something.
- It can be used with sound, light, or any other kind of wave.
- It is often used to store copies of documents, and to make 3D movies.
|
43. generating images on a screen by focusing an electronic beam on phosphorus-coated screen is called –
(a) Master Scan
(b) Total Scan
(c) Roster Scan
(d) Radar Scan
[R.A.S./R.T.S. (Pre) 1994-95]
Ans. (c) Roster Scan
- A Roster scan is a type of system used in Cathode Ray Tube monitors.
- This system involves an electronic beam being projected from an electric gun to create an image on the screen.
|
44. ‘Raman effect’ deals with the light rays passing through
(a) Only fuids
(b) Only prisms
(c) Only diamonds
(d) All transparent medium
[R.A.S./R.T.S. (Pre) 1992]
Ans. (d) Only fluids
- The Raman effect involves light passing through a transparent material.
- When a beam of light goes through a clear sample of a chemical, some of the light is scattered in different directions than the original beam.
|
45. For reproducing sound, a CD (Compact Disc) audio player uses a :
(a) Quartz crystal
(b) Titanium needle
(c) Laser beam
(d) Barium titanic ceramic
[I.A.S. (Pre) 2000]
Ans. (c) Laser beam
- The CD player uses a lens to shoot out ultraviolet laser beams that bounce off the shiny surface of the CD and turn into sound.
|
46. When a CD (compact disc used in audio and video systems) is seen in sunlight, rainbow-like colours is seen. This can be explained on the basis of the phenomenon of :
(a) Reflection and diffraction
(b) Reflection and transmission
(c) Diffraction and transmission
(d) Refraction, diffraction, and transmission
[I.A.S. (Pre) 2000]
Ans. (a) Reflection and diffraction
- When a CD is viewed in sunlight, a rainbow of colors can be seen.
- To understand why this happens, it is important to understand how a CD is made.
- A CD is a thin, circular disc made of metal and plastic.
- Most of it is made of a hard, breakable plastic called polycarbonate.
- In the middle is a thin layer of aluminum, and on top of that is a thin protective layer of plastic and lacquer.
- This acts like a film, which reflects and splits light into its colors, causing the rainbow effect.
|
47. Consider the following statements :
1. Light of longer wavelength is scattered much more than the light of shorter wavelength.
2. The speed of visible light in water is 0.95 times the speed in vacuum.
3. Radio waves are produced by rapidly oscillating electrical currents.
4. To detect over-speeding vehicles, police use the Doppler effect of reflected short radio waves.
Which of these statements are correct?
(a) 1 and 2
(b) 1 and 3
(c) 2 and 4
(d) 3 and 4
[I.A.S. (Pre) 2002]
Ans. (d) 3 and 4
- We can see that light of shorter wavelengths is scattered more than light of longer wavelengths.
- The speed of visible light in water is 2.25 x 108 m/sec, and the speed of light in a vacuum is 3.0 x 108 m/sec.
- This means that the speed of visible light in water is 0.75 times the speed of light in a vacuum.
- This means that statements 1 and 2 are wrong, while statements 3 and 4 are correct. Therefore, the correct answer is option (d).
|
48. Assertion (A) : In a motion picture, usually 24 frames are projected every second over the whole length of the film.
Reason (R) : An image formed on the retina of eye persists for about 0.1s after the removal of the stimulus.
Code :
(a) Both (A) and (R) are true and (R) is the correct explanation of (A)
(b) Both (A) and (R) are true but (R) is not a correct explanation of (A)
(c) (A) is true but (R) is false
(d) (A) is false but (R) is true
[I.A.S. (Pre) 2000]
Ans. (c) (A) is true but (R) is false
- Statement A is true, but the explanation given for it is wrong because the picture that appears on the back of the eye stays there for around 1/16 of a second after the object causing it has gone away.
|
49. Television signals cannot be received beyond a certain distance because :
(a) Signals are weak
(b) Antenna is weak
(c) Air absorbs signals
(d) The surface of the earth is curved
[U.P.P.S.C. (GIC) 2010, U.P.P.C.S. (Pre) 1994]
Ans. (d) The surface of the earth is curved
- STV signals can’t travel very far because the earth is curved. The signals travel away from the earth’s surface and keep going.
|
50. The technique used to transmit audio signals in television broadcasts is :
(a) Amplitude Modulation
(b) Frequency Modulation
(c) Pulse Code Modulation
(d) Time Division Multiplexing
[U.P.P.C.S. (Mains) 2007, I.A.S. (Pre) 1995]
Ans. (b) Frequency Modulation
- Frequency modulation is used to send sound through television.
- FM signals have a wide range of frequencies, so there is no noise or disturbance between signals on different channels.
|
51. In the human eye, light rays get transformed into neural impulses at :
(a) Cornea
(b) Pupil
(c) Retina
(d) Lens
[U.P.P.C.S. (Pre) 1997]
Ans. (c) Retina
- Light that enters our eyes is detected in the retina by cells called cones and rods.
- These cells then convert the image into electric signals which are sent through the optic nerve to the brain.
- The brain interprets these signals to allow us to see.
|
52. The image formed on Retina is :
(a) Equal to object but inverted
(b) Smaller than object but straight
(c) Smaller than object but inverted
(d) Equal to object but straight
[U.P.P.C.S. (Spl) (Mains) 2004, U.P.P.C.S. (Pre) 1995]
Ans. (c) Smaller than object but inverted
- The picture that is created on the Retina is real, but it’s flipped upside down and smaller than the original object.
- Electrical signals from the Retina travel through the optic nerve to the brain, which interprets the image and lets us see.
- Even though the Retina image is inverted, our brain is able to adjust it so that we see it correctly.
|
53. Which type of image of an object is formed by eye lens of the retina?
(a) Erect and Real
(b) Erect and Virtual
(c) Inverted and Real
(d) Inverted and Virtual
(e) None of the above
[Chhattisgarh P.C.S. (Pre) 2015]
Ans. (c) Inverted and Real
- The eye lens takes a picture of an object and turns it upside down, then projects it onto the back of the eye.
- This image is smaller than the original object.
|
54. The principal reason why it is better to have two eyes than one is that:
(a) By having two eyes we can distinguish colour easily
(b) By having two eyes we can easily see in the dark as well in dim light.
(c) It gives a man a type of vision known as mosaic vision.
(d) It enhances distance and depth perception in us.
[R.A.S./R.T.S. (Pre) 1994-95]
Ans. (d) It enhances distance and depth perception in us.
- People have the ability to see in 3D (stereopsis) because their eyes are slightly spaced apart.
- This means that our eyes capture two slightly different images of the same object, and the brain combines them to create a 3D understanding of it.
- This helps us determine the depth and distance of the object.
|
55. Direct viewing of sun during total solar eclipse causes irreversible damage to eyes. The retinal burn is caused by which one of the following components of the sun rays?
(a) Heat
(b) Rainbow light
(c) Ultraviolet light
(d) Infrared light
[U.P.P.C.S. (Mains) 2003]
Ans. (c) Ultraviolet light
- The sun can only be seen with the naked eye during a total eclipse, when the moon blocks out the sun completely.
- It is not safe to look at any other kind of eclipse (partial or annular) or the partial phases of a total solar eclipse without the right protective equipment and techniques.
- If you do not use the right methods, you may end up with permanent eye damage or severe vision loss due to the ultraviolet radiation.
|
56. The colour of the star is an indication of its :
(a) Distance from the earth
(b) Temperature
(c) Luminosity
(d) Distance from the sun
[U.P.P.C.S. (Mains) 2008, U.P.P.C.S. (Pre) 2005, U.P.P.C.S. (Mains) 2003]
Ans. (b) Temperature
- The color of stars gives an indication of their age and temperature.
- When the star is young and hot, it is blue. When the star is older and cooler, it is red.
- This is because the temperature of the star affects the type of fusion reaction and the color it reflects.
|
57. Difusion of light in the atmosphere takes place due to :
(a) Carbon dioxide
(b) Dust particles
(c) Helium
(d) Water vapours
[I.A.S. (Pre) 2003, U.P.P.C.S. (Pre) 2021]
Ans. (b) Dust particles
- Sunlight is made of different colors.
- As it passes through the atmosphere, it is scattered by the air molecules, dust particles, and other small particles that are in its way.
|
58. Diffusion of light in the atmosphere takes place due to
(a) Carbon dioxide
(b) Dust particles
(c) Helium
(d) None of the above
[Jharkhand P.C.S. (Pre) 2013]
Ans. (b) Dust particles
- Light gets scattered in the air because of dust particles.
- Diffusion is when something (like atoms, ions, molecules, or energy) moves from an area where there is more of it to an area where there is less.
|
59. The colour of light is determined by its
(a) Amplitude
(b) Wavelength
(c) Intensity
(d) Velocity
[U.P.P.C.S. (Mains) 2014, U.P.P.C.S.(Pre) 2012]
Ans. (b) Wavelength
- The colour of light is determined by its wavelength, which varies depending on the colour.
- For example, in the visible spectrum, red has the longest wavelength and violet has the shortest.
|
60. Choose the correct statement.
(a) Wavelength of red light is less than violet light
(b) Wavelength of red light is more than violet light
(c) Wavelength of violet light is more than green light
(d) Wavelength of violet light is more than yellow light
(e) None of the above / More than one of the above
[64th B.P.C.S. (Pre) 2018]
Ans. (b) Wavelength of red light is more than violet light
- VIBGYOR (Violet, Indigo, Blue Green, Yellow, Orange and Red) is the order of the different colored lights when arranged in order of increasing wavelength in the visible light spectrum.
- Violet light has the shortest wavelength and red light has the longest wavelength.
- The same order (VIBGYOR) is also the order of decreasing frequency, where violet light has the highest frequency and red light has the lowest frequency.
|
61. Which one of the colours has the longest wavelength?
(a) Green
(b) Yellow
(c) Blue
(d) Red
[M.P.P.C.S. (Pre) 1997]
Ans. (d) Red
- Red is the most far reaching color of visible light, at 700 nanometers.
- Violet is the shortest reach of visible light, at 400 nanometers.
|
62. The light with the shortest wavelength is
(a) Red
(b) Yellow
(c) Blue
(d) Violet
[Uttarakhand P.C.S. (Pre) 2005]
Ans. (d) Violet
- Violet light is the color with the shortest wavelength in the visible light spectrum.
- This wavelength is around 380 nanometers.
- The visible spectrum is the order of the different colors of light arranged from shortest to longest wavelengths.
|
63. In the visible spectrum, the colour having the shortest wavelength is :
(a) Red
(b) Yellow
(c) Blue
(d) Violet
[U.P.R.O./A.R.O. (Mains) 2014]
Ans. (d) Violet
- Violet is the light with the shortest length in the rainbow that we can see, it is about 380 to 450 nanometers long.
- Red is the longest, it is about 620 to 750 nanometers long.
|
64. Which one among the following has the highest energy?
(a) Blue light
(b) Green light
(c) Red light
(d) Yellow light
[I.A.S. (Pre) 2009]
Ans. (a) Blue light
- The energy of each color is related to its wavelength – the shorter the wavelength, the higher the energy.
- Blue has the shortest wavelength and, therefore, the highest energy, while red has the longest wavelength and the lowest energy.
|
65. Which one of the following colours of white light is least deviated by the glass prism?
(a) Green colour
(b) Red colour
(c) Violet colour
(d) Orange colour
[U.P. R.O./A.R.O. (Pre) (Re. Exam) 2016]
Ans. (b) Red colour
- The speed of white light is the same in a vacuum, but it changes when it travels through different materials.
- This means that each color of light is bent by a different amount when it passes through a material.
- Violet light is bent the most and red light is bent the least when they pass through glass.
- This means that the refractive index of glass is highest for violet light and lowest for red light.
|
66. Assertion (A): In the visible spectrum of light, red light is more energetic than green light.
Reason (R): The wavelength of red light is more than that of green light.
Code :
(a) Both A and R are individually true and R is the correct explanation of A
(b) Both A and R are individually true, but R is not a correct explanation of A
(c) A is true, but R is false
(d) A is false, but R is true
[I.A.S. (Pre) 2008]
Ans. (d) A is false, but R is true
- Red light has a longer wavelength than green light (700 nm compared to 530 nm). This means that Reason R is correct.
- The amount of energy in different colors is linked to how long their wavelength is. Red light has a lower energy than green light, which means statement (A) is incorrect.
|
67. The sun is visible to us a few minutes before the actual sunrise because of :
(a) Scattering of light
(b) Diffraction of light
(c) Total internal reflection of light
(d) Refraction of light
[R.A.S./R.T.S.(Pre) 2007]
Ans. (d) Refraction of light
- Light is bent in the atmosphere, which allows us to see the sun before it rises and after it sets.
|
68. The sun and the moon appear elliptical near the horizon because of :
(a) Refraction
(b) Optical illusion
(c) Interference phenomenon
(d) Their actual shape
[U.P.P.C.S. (Spl.) (Pre) 2008]
Ans. (a) Refraction
- The sun and moon look oval when near the ground due to bending of light.
|
69. Red light is used in traffic signals because
(a) It has the longest wavelength.
(b) It is beautiful.
(c) It is visible to people even with bad eyesight.
(d) None of the above reasons.
[U.P.P.C.S. (Mains) 2013]
Ans. (a) It has the longest wavelength
- Red has the longest wavelength, and violet has the shortest.
- This means that red light can be seen from farther away, so it’s often used in traffic signals.
|
70. Assertion (A): The danger signal is made up of red colour.
Reason (R): The red colour is scattered the least.
Select the correct answer using the codes given below:
(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true
[U.P.P.C.S. (Pre) 2007]
Ans. (a) Both (A) and (R) are true and (R) is the correct explanation of (A).
- The main purpose for using red for warning signs is because red light has the longest wavelength which makes it easier to be seen from a distance.
- The red colour of the sun as it sets is a result of other colours being scattered away and the light that reaches us is mostly red. This is why the sun appears red to us.
|
71. Red light signal is used as a danger signal because –
(a) Red light is scattered least
(b) This is comfortable for the eyes
(c) It produces the least chemical reaction
(d) It is least absorbed in air
[U.P.P.C.S. (Mains) 2008, U.P.P.C.S. (Mains) 2011, U.P.P.C.S. (Mains) 2005, U.P.P.C.S. (Pre) 1995]
Ans. (a) Red light is scattered least
- Red is used as a warning sign because it has the longest wavelength out of all the colors you can see.
- This means it is the least affected by air particles, and can travel the farthest through fog, rain, and smoke.
|
72. The Sky appears blue due to –
(a) Blue color is scattered most
(b) The red color is scattered most
(c) Blue light is minimum absorbed by atmosphere
(d) Red light is ultimately absorbed by atmosphere
[U.P.U.D.A./L.D.A. (Pre) 2013]
Ans. (a) Blue color is scattered most
- The sky looks blue because sunlight is scattered by the air molecules.
- These molecules are so small that they follow Rayleigh’s scattering, which means that the blue light in sunlight is scattered more than the other colors.
- When we look at the sky, the blue light that has been scattered is what our eyes see.
- This is why the sky is blue.
|
73. The sky is blue because –
(a) Blue colour in the sunlight is more than other colours
(b) Short waves are scattered more than long waves by atmosphere
(c) Blue colour is more absorbing to eyes
(d) Atmosphere absorbs long wavelength more than short wavelength
[Uttarakhand P.C.S. (Pre) 2005, U.P. Lower Sub. (Pre) 1998, 39th B.P.S.C. (Pre) 1994]
Ans. (b) Short waves are scattered more than long waves by atmosphere
- The sky looks blue because of the way sunlight is scattered by gases and particles in the atmosphere.
- Blue has shorter and smaller waves, so it is scattered more in all directions than other colors.
|
74. The blue colour of the sky is due to –
(a) Scattering of light
(b) Dispersion of light
(c) Interference of light
(d) Emission of more blue light as compared to other colours by the sun.
[U.P.P.C.S. (Pre) (Re. Exam) 2015]
Ans. (a) Scattering of light
- The sky appears blue because of the way sunlight is scattered in the atmosphere.
- Nitrogen and oxygen gases are the two most common particles that help scatter the higher frequency and shorter wavelength parts of visible light.
|
75. The sky appears blue due to –
(a) Diffraction of light
(b) Refection of light
(c) Refraction of light
(d) Scattering of light
[U.P.P.C.S. (Mains) 2011]
Ans. (d) Scattering of light
- The sun’s light comes to the Earth’s atmosphere and is spread in all directions by the gases and particles in the air.
- Blue light is spread around more than other colors because it moves in smaller waves.
- This is why the sky looks blue most of the time.
|
76. Consider the following statements :
1. The Sky appears blue because of scattering.
2. The main cause of the seven colours of the rainbow is the scattering of light.
3. At the time of sunrise, the sun appears red, due to scattering of light.
Choose the correct statement/s from the given options:
(a) Only 1 is true
(b) 1 and 3 is true
(c) Only 2 is true
(d) 2 and 3 is true
[Uttarakhand U.D.A./L.D.A. (Pre) 2003]
Ans. (b) 1 and 3 is true
- Light is scattered more when it has a shorter wavelength, like violet and blue.
- That’s why the sky is blue. At sunrise and sunset, the light has to travel a long way through the atmosphere so most of the other colors are scattered away.
- The only color that makes it through is red, so the sun looks red.
- Rainbows are created when light is reflected, refracted, and dispersed in water droplets, and that’s why a spectrum of colors appears in the sky. So statements 1 and 3 are correct.
|
77. The red colour of the Sun at sunset and sunrise is due to –
(a) Scattering of light
(b) Refraction of light
(c) Total internal reflection of light
(d) Dispersion of light
[U.P.P.C.S. (Mains) 2013, U.P. P.C.S. (Pre) 1992]
Ans. (a) Scattering of light
- At sunrise and sunset, the sun’s rays have to travel through more of the atmosphere because they are close to the horizon.
- This makes the other colors of light scatter away, leaving only red.
- This is why the sun and sky look red at these times.
|
78. An astronaut sees the colour of the sky as –
(a) Blue
(b) White
(c) Black
(d) Red
[U.P.P.C.S. (Mains) 2005]
Ans. (c) Black
- An astronaut sees the sky as being black because there is no atmosphere in space.
- The sunlight can’t be reflected or scattered off any air particles, so they observe everything around them as black.
|
79. When we see the sky from a plane in high altitude, then it seems –
(a) Blue
(b) Black
(c) White
(d) Red
[U.P.P.S.C. (R.I.) 2014]
Ans. (b) Black
- People on planes can see that the sky is dark when they are flying high because there is no air at these heights.
- The light from the sun can’t spread out and be seen.
|
80. The sea seems blue due to –
(a) Excess deepness
(b) Refection of sky and scattering of light by the drops of water
(c) Blue colour of water
(d) Upper layer of water
[40th B.P.S.C. (Pre) 1995]
Ans. (b) Refection of sky and scattering of light by the drops of water
- The sea appears blue because the sky is reflected off it and light is scattered by the water droplets.
- Light scatters when it passes through air or water, and since blue light has the shortest wavelength, it is the most easily scattered.
|
81. The (Green) Grass appears green to us because :
(a) It refects green colour light to our eyes
(b) It absorbs green colour light
(c) It refects all other colour lights except that of green colour
(d) None of the above
[U.P. P.C.S. (Mains) 2017]
Ans. (a) It refects green colour light to our eyes
- The color that we see on an object is not actually the color that is inside it.
- If something looks green, that means it takes in all colors except green.
- If it looks black, that means no color is bouncing off it.
- If something is white, it reflects all light.
|
82. Suppose a rocketship is proceeding from the earth at a speed of 2/10th the velocity of light. A light in the rocketship appears blue to the passengers on the ship.
What colour would it appear to an observer on the earth?
(a) Blue
(b) Orange
(c) Yellow
(d) Yellow-Orange
[I.A.S. (Pre) 1995]
Ans. (c) Yellow
- To determine the color that would appear to an observer on the earth, we use the following formula.
- Where λ = Prime wavelength
- λo = Virtual wavelength
- ν = Velocity of rocket
- C = Velocity of light
- Because the rocket is proceeding from the earth, thus positive sign is taken.
- 2/10 C = (λ – λ0/λ) C
- 2/10 = (λ – λ0/λ)
- 2/10 = 1 – λ0/λ
- λ0/λ = 1- 2/10
- λ0/λ = 8/10
- λ = 10/8 λ0 = 1.25λo
- The blue light that we see from Earth has a wavelength range between 562.5 and 593.75 nanometers, which is a type of yellow light.
- This range is between 450 and 475 nanometers for blue light.
|
83. What will be the nature of image formed by a convex mirror when the position of object is between infinity and pole P of the mirror?
(a) Virtual and erect
(b) Real and erect
(c) Real and inverted
(d) Virtual and inverted
[Chhattisgarh P.C.S. (Pre) 2020]
Ans. (a) Virtual and erect
- When an object is placed between the infinity point and the pole of a convex mirror, the image of the object will be created between the pole and the focus, which is located behind the mirror.
- This image is smaller, not real, and upright.
|
84. In driving a car which type of mirror would you like to use for observing trafc at your back ?
(a) Concave mirror
(b) Spherical mirror
(c) Convex mirror
(d) Plain mirror
[Uttarakhand P.C.S. (Pre) 2005, U.P. P.C.S. (Pre) 1991]
Ans. (c) Convex mirror
- A convex mirror has a bigger view of the cars behind you compared to a regular mirror of the same size.
- It makes an upright and smaller picture, and since it curves outward, it can see more of what’s behind you.
|
85. Which one of the following types of mirror is used to see the traffic behind the car?
(a) Convex mirror
(b) Concave mirror
(c) Plane mirror
(d) Spherical mirror
[U.P.P.C.S. (Pre) 2015]
Ans. (a) Convex mirror
- Convex mirrors are used in vehicles to see behind them.
- They are usually seen as rear-view mirrors or side-mirrors in cars, trucks, and buses.
|
86. Which mirror is used as a rearview mirror in vehicles?
(a) Plain
(b) Convex
(c) Concave
(d) Cylindrical
[U.P.P.C.S (Pre) 2011, U.P.P.C.S. (Mains) 2010]
Ans. (b) Convex
- Convex mirrors are used in car rear view mirrors.
- This is because they create an upright, smaller version of objects that are far away, while providing a wider view.
|
87. For shaving, one uses –
(a) Concave mirror
(b) Plain mirror
(c) Convex mirror
(d) None of these
[43rd B.P.S.C. (Pre) 1999]
Ans. (a) Concave mirror
- A concave mirror is used for shaving because when a man stands between the focal point and the center of the concave mirror, he can see an enlarged version of his face, which is both real and imaginary.
- This is why a concave mirror with a long focal length is used for shaving.
|
88. The mirror, which is used in searchlights, is –
(a) Concave mirror
(b) Convex mirror
(c) Simple mirror
(d) None of these
[U.P.P.C.S.(Mains) 2009]
Ans. (a) Concave mirror
- A concave mirror is used in car headlights and searchlights.
- It takes a light source and turns it into a beam of light that is parallel.
|
89. A dentist mirror is a –
(a) Cylindrical mirror
(b) Concave mirror
(c) Convex mirror
(d) Plane mirror
[U.P.P.C.S. (Mains) 2009]
Ans. (b) Concave mirror
- Dentists use concave mirrors because they create enlarged, right-side-up images when placed close to an object (closer than the focal length).
- This is helpful for finding and fixing issues with teeth, such as cavities, cracks, or other issues.
|
90. The mirror used by a dentist to examine the teeth of patients is
(a) Concave
(b) Convex
(c) Plane
(d) Cylindrical
[U.P.P.C.S.(Pre) 2013, U.P.P.C.S. (Pre) (Re. Exam) 2015]
Ans. (a) Concave
- Dentists use special mirrors that are curved inward to look closely at teeth and other parts of the mouth.
- This type of mirror creates a bigger and upright picture when the object is put near the center.
|
91. In order to avoid sunlight, which of the following colour combination for an umbrella is most appropriate?
(a) Top black & bottom white
(b) Top white & bottom black
(c) Only black
(d) Only white
[U.P.P.C.S. (Pre) 1993]
Ans. (b) Top white & bottom black
- Option (b) of a white top and black bottom umbrella is the best choice if you want to stay cool and safe from the sun’s rays.
- The white will reflect most of the sunlight while the black will absorb what gets through the white layer.
|
92. The image formed by an astronomical telescope is
(a) Virtual and diminished
(b) Virtual and magnified
(c) Real and diminished
(d) Real and magnified
[U.P.P.C.S. (Mains) 2013]
Ans. (b) Virtual and magnified
- An astronomical telescope is a tool used to make heavenly objects look bigger and closer.
- The image seen through the telescope is upside down and not real.
|
93. The number of images of an object placed between two parallel mirrors is :
(a) Two
(b) One
(c) Six
(d) Infinite
[U.P.P.C.S.(Mains) 2013, U.P.P.C.S. (Pre) 1994]
Ans. (d) Infinite
- When an object is put between two mirrors that are parallel to each other, an unlimited number of images will be created.
- Each image will come from a reflection. If the two mirrors are at an angle, you can figure out how many images will be made by dividing 360 degrees by the angle and subtracting one.
|
94. How many images will be formed if a point light source is placed between two parallel plane mirrors?
(a) Two
(b) Four
(c) Eight
(d) Infinite
[U.P.P.C.S. (Pre) 2015]
Ans. (d) Infinite
- When something is put between two mirrors that are side by side, it creates an endless number of reflections.
- This is because the mirrors are reflecting off of each other, creating multiple images.
|
95. When a mirror is rotated by an angle θ, the reflected ray will rotate by :
(a) 0
(b) θ/2
(c) θ
(d) 2θ
[I.A.S. (Pre) 1996]
Ans. (d) 2θ
- If you turn a plane mirror a certain amount, the reflected light will turn twice as much.
- For example, if you turn the mirror by an angle θ, the reflected light will turn by 2θ.
|
96. Assertion (A):Small glass beads fixed on traffic signals glow brightly when light falls upon them.
Reason (R) : Light is totally reflected when the angle of incidence exceeds a certain critical value and light travelling in a denser medium is reflected from a rarer medium.
Code :
(a) Both (A) and (R) are true and (R) is the correct explanation of (A)
(b) Both (A) and (R) are true but (R) is not a correct explanation of (A)
(c) (A) is true but (R) is false
(d) (A) is false but (R) is true
[I.A.S. (Pre) 2000]
Ans. (a) Both (A) and (R) are true and (R) is the correct explanation of (A)
- When light moves from a denser material (like small glass beads) to something less dense, it will totally reflect if it hits the surface at a certain angle.
- This is called total internal reflection.
- Traffic signals shine brightly because of this effect. Both statements (A) and (R) are true, and (R) explains (A) correctly.
|
97. Light is made of seven colours. What is the method of separating the colours?
(a) The colours can be separated by a prism
(b) The colours can be separated by a flter
(c) The colours can be separated by plants
(d) The colours cannot be separated
[47th B.P.S.C. (Pre) 2005]
Ans. (a) The colours can be separated by a prism
- Colors can be split up by using a prism. White is made up of all seven colors.
- When it goes through the prism, because of different wavelengths, each color of light is refracted in a different way.
|
98. The correct order of colours in a rainbow is :
(a) Blue, green, violet
(b) Violet, green, blue
(c) Blue, yellow, green
(d) Blue, green, yellow
[R.A.S./R.T.S.(Pre) 1999]
Ans. (d) Blue, green, yellow
- Rainbows are created when light is reflected, bent, and split in water droplets.
- This results in a colorful arc of light in the sky, with the colors usually appearing in this order:
- Violet, Indigo, Blue, Green, Yellow, Orange, and Red.
|
99. A rainbow is produced when sunlight falls on drops of rain. which of the following physical phenomena are responsible for this?
1. Dispersion
2. Refraction
3. Internal reflection
Select the correct answer using the code given below :
(a) 1 and 2
(b) 2 and 3
(c) 1 and 3
(d) All of these
[I.A.S. (Pre) 2013]
Ans. (d) All of these
- A rainbow appears when sunlight hits a raindrop at a certain angle.
- The sunlight is bent, or refracted, when it enters the raindrop, and it is then split into its seven different colours.
- This is caused by refraction, dispersion, and internal reflection.
|
100. Dispersion of light is possible by :
(a) Prism
(b) Convex lens
(c) Concave lens
(d) Simple mirror
(e) None of the above/More than one of the above
[66th B.P.S.C. (Pre) (Re. Exam) 2020]
Ans. (a) Prism
- A prism can break up white light into its separate colors, which is called dispersion.
|
101. Which one of the following colours is seen in the middle of a Rainbow ?
(a) Blue
(b) Green
(c) Red
(d) Yellow
[U.P.P.C.S. (Mains) 2012]
Ans. (b) Green
- The colors of the rainbow, in the right order, are Red, Orange, Yellow, Green, Blue, Indigo and Violet.
- This means that the color ‘Green’ is in the center of the rainbow (with the acronym VIBGYOR).
|
102. The terminal color bands of the rainbow are :
(a) Blue and Orange
(b) Green and Red
(c) Yellow and Green
(d) Violet and Red
[U.P. Lower Sub. (Mains) 2015]
Ans. (d) Violet and Red
- A rainbow occurs when sunlight is reflected, refracted, and dispersed through water droplets in the sky.
- It creates a spectrum of colors, usually in the order of red, orange, yellow, green, blue, indigo, and violet. Therefore, option (d) is the correct answer.
|
103. In which direction the rainbow is seen at 12 noon?
(a) In the West
(b) In the South
(c) In the East
(d) It cannot be seen
[43rd B.P.S.C. (Pre) 1999]
Ans. (d) It cannot be seen
- A rainbow is located opposite to the sun; this explains why rainbow is not seen at 12 noon with the sun overhead.
|
104. Assertion (A) : A stick is dipped in water in a slanting position. If observed sideways, the stick appears short and bent at the surface of the water.
Reason (R) : A light coming from the stick undergoes scattering from water molecules giving the stick a short and bent appearance.
Code :
(a) Both (A) and (R) are true and (R) is the correct explanation of (A)
(b) Both (A) and (R) are true but (R) is not a correct explanation of (A)
(c) (A) is true but (R) is false
(d) (A) is false but (R) is true
[I.A.S. (Pre) 2001]
Ans. (c) (A) is true but (R) is false
- When a stick is put in water at an angle, it looks shorter and curved at the surface of the water.
- This happens because of refraction of light. When you put the stick in water, it is going from a less dense area to a denser one.
- Light rays bend away from the normal when they move from a less dense to a denser medium.
- That is why the stick looks like it is bending and shorter when it is in the water.
|
105. Consider the following statements :
1. If a person looks at a coin which is in a bucket of water, the coin will appear to be closer than it really is.
2. If a person under water looks at a coin above the water surface, the coin will appear to be at a higher level than it really is.
Which of the above statements is/are correct ?
(a) 1 and 2
(b) 1 alone
(c) 2 alone
(d) Neither 1 nor 2
[I.A.S. (Pre) 1999]
Ans. (a) 1 and 2
- Statement 1 is correct. The coin will look closer than it actually is because the light is bent when it passes from water to air.
- Srtatement 2, If someone is underwater and looks at a coin above the water, the coin will appear to be higher than it really is because of the bending of light. This happens because the light is going from a less dense medium to a more dense one.
|
106. An air bubble in water will act like a :
(a) Convex mirror
(b) Convex lens
(c) Concave mirror
(d) Concave lens
[U.P. Lower Sub. (Pre) 2013, U.P. U.D.A./L.D.A. (Spl) (Pre) 2010, U.P.P.C.S. (Spl) (Pre) 2008, I.A.S. (Pre) 1995]
Ans. (d) Concave lens
- A bubble of air underwater is shaped like a curved lens.
- The water it is in is more bendy than the air, so it changes how the lens works and makes it so the light coming through it spreads out.
|
107. An air bubble inside water behaves as a:
(a) Bifocal lens
(b) Convergent lens
(c) Divergent lens
(d) Cylindrical lens
[U.P.P.C.S. (Pre) 2002]
Ans. (c) Divergent lens
- A bubble of air underneath water has a curved surface that works like a lens that makes things look farther away (diverging lens).
- The water has a higher refractive index than the air, which changes the way the bubble behaves like a lens.
|
108. Two glass lenses of same focal length, one being convex and the other concave, are kept in contact, the combination will act as :
(a) convergent lens
(b) divergent lens
(c) plane glass sheet
(d) mirror
[U.P.P.S.C. (GIC) 2017]
Ans. (c) plane glass sheet
- If a convex lens and a concave lens of the same size are put together, the focal length of the combination will be very large and it will be like looking through a flat piece of glass.
|
109. The minimum height of a plane mirror to see the full-size image of a person is equal to –
(a) The height of the person
(b) Half the height of the person
(c) One-fourth the height of the person
(d) Double the height of the person
[U.P.P.C.S. (Pre) 2014, U.P.P.C.S. (Pre) 2011, U.P.P.C.S. (Mains) 2011, U.P. U.D.A./L.D.A. (Spl) (Mains) 2010]
Ans. (b) Half the height of the person
- A person must have a mirror that is at least half their height in order to be able to see their full reflection.
- Using the principle of reflection, the angle of the light hitting the mirror has to be the same as the angle the light reflects off the mirror.
- When light travels from a person’s feet and reaches their eyes, they can see their full reflection.
- This means that the mirror needs to be half the height of the person.
|
110. The minimum height of mirror required to see whole stand up image of a man of height 1.50 meter shall be
(a) 0.75 metre
(b) 1.00 metre
(c) 1.50 metre
(d) 3.00 metre
[U.P.P.S.C. (R.I.) 2014]
Ans. (a) 0.75 metre
- In order to see full-length image, the minimum height of the mirror required is half of a person’s height. Therefore, minimum height of mirror required = 1.50/2 metre = 0.75 metre.
|
111. The radius of curvature of the plane mirror is :
(a) Zero
(b) One
(c) Infinity
(d) Between one and infinity
[U.P. Lower Sub. (Pre) 2015]
Ans. (c) Infinity
- A plane mirror is a type of curved mirror with a radius that never ends.
- This type of mirror reflects an image back at the same distance away as the object is from the mirror.
- That is,
- do = distance of the object from the mirror
- di = distance of reflection from the mirror
- 1/d0 + 1/di = 2/r (here r = radius of curvature)
- But for the plane mirror
- thus, 2/r = 0 or, 2/0 or r = ∞
- Thus, the radius of curvature of the plane mirror is considered as infinity.
|
112. To remove the defect of long-sightedness one uses –
(a) Concave lens
(b) Convex mirror
(c) Convex lens
(d) Concave mirror
[43rd B.P.S.C. (Pre) 1999, Chhattishgarh P.C.S. (Pre) 2016]
Ans. (c) Convex lens
- Hypermetropia, also known as far-sightedness, is a condition in which you can see things far away, but not close up. To fix this, you need a convex lens.
|
113. Which one of the following statements is not true for a person sufering from hypermetropia?
(a) The person can see far objects distinctly.
(b) The focal length of the lens is large.
(c) The image of the close objects is focused behind the retina.
(d) A concave lens is used to correct this defect.
[U.P.P.C.S. (Pre) 2010]
Ans. (d) A concave lens is used to correct this defect.
- Hypermetropia is a common vision issue and it affects around 25% of people.
- People with hypermetropia can see things that are far away clearly, but they have trouble seeing things close up.
- It happens when the light entering the eye focuses behind the retina instead of on it.
- For farsighted people, their eyeballs are shorter than normal. A convex lens can be used to fix this problem.
|
114. Reading glasses are made from which type of lenses?
(a) Concave
(b) Convex
(c) Plain
(d) None of these
[44th B.P.S.C. (Pre) 2000]
Ans. (b) Convex
- A convex lens is thicker in the middle and thinner at the edges.
- It causes light to come together, and is also known as a converging lens.
- It is used in reading glasses and to treat far-sightedness.
|
115. Which of the following lenses is used to minimize Myopia?
(a) Convex lens
(b) Concave lens
(c) Cylindrical lens
(d) None of these
[U.P.P.C.S. (Mains) 2011, M.P.P.C.S. (Pre) 2008]
Ans. (b) Concave Lens
- A concave lens is used to minimize the defect of myopia.
|
116. A myopic eye can be corrected by using a
(a) Convex lens
(b) Concave lens
(c) Cylindrical lens
(d) Plane Convex lens
[U.P.P.C.S. (Mains) 2008, U.P. Lower Sub. (Pre) 2002]
Ans. (b) Concave lens
- Myopia, or near-sightedness, is a problem with the way the eye bends light which makes it hard to see things far away.
- Objects that are close up look clear, but things far away appear blurry.
- To fix it, you wear a special type of lens called a concave lens.
|
117. For the myopic eye, the defect is cured by –
(a) Convex lens
(b) Concave lens
(c) Cylindrical lens
(d) None of the above
[U.P.P.C.S. (Mains) 2013]
Ans. (b) Concave lens
- In Myopia, close objects look clear but distant objects appear blurred. It is corrected by using a concave lens.
|
118. When a person enters into a dark room from the strong light area, he is not able to see clearly for some time. Later he gradually begins to see things, This is because-
(a) Changes in the size of pupil
(b) Changes in the diameter and focal length of lens
(c) Bleaching and reformation of Rhodopsins
(d) Eyes become familiar with darkness in course of time
[R.A.S./R.T.S.(Pre) 2008]
Ans. (*)
- When you enter a darkroom from a bright light, it takes time for your eyes to adjust.
- This is because the size of the pupil of your eye is small, so very little light enters.
- In time, the pupil expands, allowing more light to come in and then you can see.
- This is because of two types of cells in our retina that absorb light. The rods help us to see in the dark and the cones help us to see in bright conditions.
- When we go from light to dark, the cones stop working, so it takes time for the rods to adjust.
|
119. The focus in the eye is done by
(a) Change in the convexity of the lens
(b) To and fro movement of the lens
(c) To and fro movement of the retina
[(d) Change in the refractive index of the eye fuid]
U.P.P.S.C. (R.I.) 2014
Ans. (a) Change in the convexity of the lens
- Our eyes bend light so we can see the world around us.
- The cornea and the humor stay the same, but the lens can change shape to focus the light onto the retina.
- The more the lens bulges out, the more it bends the light, and the flatter it is, the less it bends the light.
|
120. The change of focal length of an eye lens is caused by action of the
(a) Pupil
(b) Retina
(c) Ciliary muscles
(d) Iris
(e) None of the above
[Chhattisgarh P.C.S. (Pre) 2014]
Ans. (c) Ciliary muscles
- The eye lens is made up of fibres and jelly-like material. The ciliary muscles can make it slightly bend.
- When the muscles are relaxed, the lens becomes thinner and its focal length increases, allowing us to see far away objects clearly.
- When we look at things close to us, the ciliary muscles contract, causing the lens to become thicker and its focal length to decrease, so we can see things closer to us better.
|
121. Which one of the following statement is not correct ?
(a) Mirage is an optical illusion arising due to total internal refection of light
(b) Concave mirrors are used in searchlights
(c) In summer, white or light coloured clothes are preferred to dark coloured clothes generally
(d) A convex mirror with a small aperture is used by doctors to examine, ear, nose or throat of a patient.
[U.P.P.C.S. (Mains) 2010]
Ans. (d) A convex mirror with a small aperture is used by doctors to examine, ear, nose or throat of a patient
- Doctors often use a head mirror to look into someone’s ears, nose, and throat.
- It has a round mirror with a tiny hole in the middle and is held on with a headband. Statement (d) is wrong, but the other statements are correct.
|
122. The least distance of distinct vision is (cm.)
(a) 25
(b) 5
(c) 75
(d) 100
[U.P.P.C.S. (Mains) 2008]
Ans. (a) 25
- The human eye can usually create a clear image of an object if it is located anywhere from far away to a certain point called the “Near Point”.
- The closest distance an object can be from the eye to have a clear image is called the “least distance of distinct vision”.
- It is usually 25 cm for a normal eye and is referred to as ‘D’.
|
123. For normal eyes what is the minimum distance for clear vision?
(a) 10 cm.
(b) 15 cm.
(c) 20 cm.
(d) 25 cm.
(e) 30 cm.
[Chhattisgarh P.C.S. (Pre) 2013]
Ans. (d) 25 cm.
- A normal human eye needs to be 25 cm away from an object in order to have clear vision.
- This is also called the closest distance an eye can be from something and still be able to see it clearly.
|
124. The minimum distance of clear vision for a normal healthy eye of a human being is supposed to be :
(a) 50 cm
(b) 10 cm
(c) 15 cm
(d) 25 cm
[M.P. P.C.S. (Pre) 2016]
Ans. (d) 25 cm
- The closest distance a person can be to be able to see something clearly is 25 cm.
- This is sometimes referred to as the near point of the eye.
- The human eye is an organ that can take in images and send them to the brain.
|
125. The power of a lens is measured in
(a) dioptre
(b) aeon
(c) lumen
(d) candela
[M.P.P.C.S. (Pre) 2017]
Ans. (a) dioptre
- Dioptre is the unit used to measure how strong a lens is. It is found by taking the opposite of the length of the lens in metres.
- If a lens is converging, it has a positive power; if it’s diverging, it has a negative power.
|
126. The power of the lens is measured in the:
(a) Watt
(b) Ampere
(c) Volt
(d) Dioptre
(e) None of the above/More than one of the above
[66th B.P.S.C. (Pre) (Re. Exam) 2020]
Ans. (d) Dioptre
- A lens’ strength is shown in diopters (D).
- If it is a convex lens, the number will be positive, and if it is a concave lens, the number will be negative.
|
127. If the lens power of glass is +2 dioptre, its focal length will be-
(a) 200 cm
(b) 100 cm
(c) 50 cm
(d) 2 cm
[41st B.P.S.C. (Pre) 1996]
Ans. (c) 50 cm
We know that,
- (D = 1/f)
- 1metre=100 cm
- f = 100/D cm
- f = 100/2 = 50 cm
|
128. The power of the sunglass is –
(a) 0 Dioptre
(b) 1 Dioptre
(c) 2 Dioptre
(d) 4 Dioptre
[U.P.P.C.S. (Pre) 1995]
Ans. (a) 0 Dioptre
- The power of the sunglass is 0 dioptre.
|
129. Which one of the following combinations of aperture and shutter speed of a camera will allow the maximum exposure?
(a) f-22, 1/60
(b) f-16, 1/125
(c) f-8, 1/250
(d) f-5. 6, 1/1000
[I.A.S. (Pre) 1994]
Ans. (a) f-22, 1/60
- The exposure value EV is EV ∝ N² × t where N is the relative aperture and t is the exposure time hence, among the above options (a) has maximum exposure value.
|
130. The retina of the eye is comparable to which of the following parts of a traditional camera?
(a) Film
(b) Lens
(c) Shutter
(d) Cover
[U.P.P.C.S (Pre) 2011]
Ans. (a) Film
- The back of your eye has a layer called the retina.
- It works like the film in an old-fashioned camera.
- The macula, the center part of the retina, helps you see clearly.
- The retina’s nerve cells turn light into electrical signals and send them to the brain through the optic nerve.
|
131. In the human eye, the image of an object forms at
(a) Cornea
(b) Iris
(c) Pupil
(d) Retina
[M.P.P.C.S. (Pre) 2017, 2014, Uttarakhand Lower Sub. (Pre) 2010]
Ans. (d) Retina
- The way the human eye works is similar to how a camera works.
- Light rays enter the cornea and are bent by the cornea and the lens.
- For a normal eye, the image formed is sent from the retina to the brain through the optic nerve, and the image is seen right-side-up.
|
132. The human eye forms the image of an object at its –
(a) Cornea
(b) Iris
(c) Pupil
(d) Retina
(e) None of the above
[Chhattisgarh P.C.S. (Pre) 2014]
Ans. (d) Retina
- In a typical eye, the picture created is sent from the back of the eye to the brain through the optic nerve.
- The brain then processes the information so that the image is seen the correct way.
|
133. In long-sightedness, images are formed at the following :
(a) On Retina
(b) In front of Retina
(c) Behind Retina
(d) On Blind Spot
[U.P. R.O./A.R.O. (Mains) 2017]
Ans. (c) Behind Retina
- In long-sightedness, far away objects appear clear but close objects appear blurry because the image is formed behind the retina.
- This happens when the eyeball is too short or the eye lens has a longer focal length.
- To fix this, a convex lens is used.
|
134. The colour of an opaque object is due to the colour it–
(a) Absorbs
(b) Refracts
(c) Reflects
(d) Scatters
[I.A.S. (Pre) 1994]
Ans. (c) Reflects
- Opaque objects don’t let light through them.
- Instead, they absorb some of the light that hits them and reflect the rest, which is the same color as the object.
|
135. Colour in a colour television is produced by a combination of three basic colours, they are :
(a) Red, blue and orange
(b) Red, green and blue
(c) Red, yellow and green
(d) Red, green and brown
[R.A.S./R.T.S. (Pre) 1992]
Ans. (b) Red, green and blue
- The CRT in color TV uses three different phosphors that give off red, green, and blue light.
- They are grouped in “triads” of stripes or clusters.
|
136. Which primary colours produce different shades on the TV screen?
(a) Red, green and blue
(b) Red, yellow and green
(c) Orange, green and purple
(d) Red, yellow, green and black
[Uttarakhand Lower Sub. (Pre) 2010]
Ans. (a) Red, green and blue
- Computer screens and TVs produce three different colors of light (red, green, and blue).
- The various colors we see are created when those three colors are mixed and varied in intensity.
- Every pixel on a computer screen is made up of three tiny dots of substances called phosphors, which are enclosed by a black frame.
|
137. When beams of red, blue, and green lights fall on the same spot, the color of the light becomes :
(a) Violet
(b) Red
(c) Yellow
(d) White
[R.A.S./R.T.S. (Pre) 2003]
Ans. (d) White
- Red, green and blue are known as the primary colors for light.
- We mix them together to make a color, so they are known as additive colors.
- Cyan, Magenta and yellow are known as subtractive colors because when we use them, it takes away color from white light.
- When we mix all 3 primary colors of light in equal amounts, we get white light.
|
138. Which is not a primary color?
(a) Black
(b) Yellow
(c) Red
(d) Blue
[M.P.P.C.S. (Pre) 2015]
Ans. (a) Black
- Black is not considered a main color.
- In painting, the main colors are red, yellow, and blue, but when it comes to science and light, the main colors are red, green, and blue.
|
139. Three colors are the primary colors. These are –
(a) Blue, Yellow and Red
(b) Blue, Green and Red
(c) Yellow, Green and Red
(d) Blue, Yellow and Red
[M.P.P.C.S. (Pre) 2005]
Ans. (b) Blue, Green and Red
- This color wheel has three main colors (Primary Colors): Red, Yellow, and Blue. It also has three additional colors (Secondary Colors): Orange, Green, and Violet.
|
140. Consider the following statements :
1. If magenta and yellow coloured circles intersect, the intersected area will have a red colour.
2. If cyan and magenta coloured circles intersect, the intersected area will have a blue colour.
Which of the statements given above is/are correct?
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2
[I.A.S. (Pre) 2007]
Ans. (c) Both 1 and 2
- If we mix the three primary colors, red, green and blue, we will get white.
- The primary pigment colors are cyan, magenta and yellow.
- Mixing magenta and yellow leads to the color red. Mixing cyan and magenta produces blue.
- Lastly, if we mix cyan and yellow we will get the color green. All of these statements are correct.
|
141. The number of colors contained in the sunlight is –
(a) 3
(b) 5
(c) 6
(d) 7
[U.P.P.C.S. (Mains) 2015]
Ans. (d) 7
- We all know that sunlight is a white light and it has seven colors.
- This splitting of the light into its individual colors (VIBGYOR; violet, indigo, blue, green, yellow, orange, and red) is known as light dispersion.
- A prism is used to separate the light into its different components.
|
142. Find out the odd color from the following options-
(a) Green
(b) Brown
(c) Red
(d) Yellow
[R.A.S./R.T.S. (Pre) 1999]
Ans. (b) Brown
- Brown is an unusual color because it does not fit into the traditional color spectrum of ROYGBIV (red, orange, yellow, green, blue, indigo, and violet).
- White light is a combination of these colors, so brown does not appear in the mix.
|
143. Consider the following phenomena-
1. Size of the Sun at dusk
2. Colour of the Sun at dawn
3. Moon being visible at dawn
4. Twinkle of stars in the sky
5. Polestar being visible in the sky
Which of the above are optical illusions?
(a) 1, 2, and 3
(b) 3, 4 and 5
(c) 1, 2 and 4
(d) 2, 3 and 5
[I.A.S. (Pre) 2013]
Ans. (c) 1, 2 and 4
- The sun looks smaller at noon, but appears larger at dawn or dusk.
- When it is dawn, the sun looks bigger because it is seen with other objects on the horizon.
- The color of the sun at dawn is an illusion too.
- The twinkling of stars is also an illusion that is caused by the refraction of light when it passes through different layers of the atmosphere.
|
