1. A 100-watt electric bulb is used for 10 hours. What will be the cost of electricity consumed, if the consumption cost is Rs. 5 per unit?
(a) Rs. 5
(b) Rs. 10
(c) Rs. 25
(d) Rs. 50
[R.A.S./R.T.S.(Pre) 2012]
Ans. (a) Rs. 5
- Energy Consumption of a 100-watt electric bulb which is used for 10 hours = 100 ×10
= 1000 watt-hour
= 1 kilowatt-hour
= 1 unit.
- According to the question the cost of 1 unit of electricity = Rs 5.
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2. If a bulb of 100 watt burns for 10 hours, the expenditure of electricity will be –
(a) 0-1 unit
(b) 1 unit
(c) 10 units
(d) 100 units
[41st B.P.S.C. (Pre) 1996]
Ans. (b) 1 unit
- Energy Consumption of a 100-watt electric bulb which is used for 10 hours = 100 ×10
= 1000 watt-hour
= 1 kilowatt-hour
= 1 unit.
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3. Five bulbs each of 100-watt capacity in a tunnel are illuminated continuously for twenty hours. The consumption of electricity will be:
(a) One unit
(b) Two units
(c) Ten units
(d) Twenty units
[U.P.P.C.S. (Pre) 2017]
Ans. (c) Ten units
- Consumption of electricity by one bulb
- (No. of Units) = watt×hours/1000
= 100×20/1000
= 2 Unit
- Thus consumption of electricity by 5 bulbs = 2 × 5 = 10 units
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4. The value of 1 kilowatt hour is –
(a) 3.6 × 106J
(b) 3.6 × 103J
(c) 103 J
(d) 105J
[U.P.P.C.S. (Pre) 2006]
Ans. (a) 3.6 × 106J
- 1 Kilowatt hour = 1 (kilowatt) (1 hour)
= (1000 joule/sec.) (3600 sec.)
= 36 × 105 Joule
= 3.6 × 106 Joule
- Thus, option (a) is correct.
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5. An electric bulb of 100 watts is used for 4 hours. The unit of electric energy used is-
(a) 400
(b) 25
(c) 4
(d) 0.4
[U.P. Lower Sub. (Pre) 2009]
Ans. (d) 0.4
- The electric energy consumed = 100 watt × 4 hour = 400 watt-hour
= 400/1000 kilowatt hour
= 0.4 kilowatt-hour
= 0.4 unit
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6. Electricity consumption bill is based on the measurement of –
1. Watt
2. Voltage
3. Ohm
4. Ampere
Select your answer to the following codes –
(a) Only 1
(b) 1 and 2
(c) 2 and 3
(d) 1 and 4
[40th B.P.S.C. (Pre) 1995]
Ans. (a) Only 1
- The electricity bill is calculated by how much electricity is used, measured in kilowatt hours.
- 1 kilowatt hour is equal to using 1,000 watts of electricity in 1 hour.
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7. How many units of electricity will be consumed if you use a 60-watt electric bulb for 5 hours every day for 30 days?
(a) 12
(b) 9
(c) 6
(d) 3
[R.A.S./R.T.S. (Pre) 2003]
Ans. (b) 9
- We know that number of units= watt × hour/1000
60×35×5/1000 = 9 unit
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8. An electric bulb is connected to a 220 v generator. The current is 0.5 A. The power of the bulb is
(a) 110 w
(b) 110 v
(c) 440 w
(d) 220 w
(e) None of these
[Chhattisgarh P.C.S. (Pre) 2016]
Ans. (a) 110 w
- Given,
v = 220 v
i = 0.5 A
- we know that,
P = w/t = vit/t (w = vit)
= vi = 220×0.5 ⇒ 110 watt
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9. The total resistance of a circuit having two parallel resistors is 1.403 kilo-ohm. If one of the resistors is 2.0 kilo-ohm, then the other resistor will be
(a) 1.403 kilo-ohm
(b) 2.0 kilo-ohm
(c) 3.403 kilo-ohm
(d) 4.70 kilo-ohm
(e) None of the above/More than one of the above
[66th B.P.S.C. (Pre) 2020]
Ans. (d) 4.70 kilo-ohm
- If the total resistance of a parallel circuit is R, then
1/R = 1/R1 + 1/R2 ………….
- According to the question,
1/1.403 = 1/2 + 1/R2
or, 1/R2 = 1/1.403 – 1/2
or, 1/R2 = 2- 1.403/2.806
or, R2 = 2.806/0.597 = 4.70 kilo-ohm
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10. Of the two bulbs in a house, one glows brighter than the other. In this context which of the following statements is correct?
(a) The brightness does not depend on the resistance.
(b) Both the bulbs have same the resistance.
(c) The bright bulb has larger resistance.
(d) The dim bulb has a larger resistance.
[U.P. Lower Sub. (Pre) 2008, U.P.P.C.S. (Pre) 2009]
Ans. (d) The dim bulb has a larger resistance
- The bulb that decays more energy will generate more brightness.
Power (P) = Voltage (V) × Current (I)
It is known that V = I × Resistance (R)
P = V²/R; P ∝ 1/R Thus, the bulb of high resistance decays low energy and will generate dim light.
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11. Of the two bulbs in a house, one glows brighter than the other. Which of the two has a larger resistance?
(a) The dim bulb
(b) The brighter bulb
(c) Both have the same resistance
(d) The brightness does not depend on the resistance
[U.P.P.C.S. (Mains) 2013]
Ans. (a) The dim bulb
- If the light bulb is brighter, it has more energy and less resistance.
- Conversely, if the bulb is dimmer it has less energy and more resistance.
- This means the dimmer bulb has a higher resistance.
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12. How two identical bulbs should be connected to get maximum light?
1. Both are connected in series.
2. Both are connected in parallel.
Select the correct answer using the code given below :
Code :
(a) In case 1 more
(b) In case 2 more
(c) Same in both 1 and 2
(d) Nothing can be said
[U.P. R.O./A.R.O. (Pre) 2021]
Ans. (b) In case 2 more
- When two or more light bulbs are connected in parallel, they are brighter than if they were connected in series.
- This is because each bulb in the parallel circuit has the same voltage as the circuit, and the overall electrical resistance is lower.
- This means that the power of each bulb is greater, because it is calculated by V2/R, where V is the voltage of the bulb and R is the electrical resistance.
- The total resistance of the series circuit is
- The total resistance of the parallel circuit is
- 1/Rparallel = 1/R + 1/R
- Rparallel = R/2.
- Thereby, the power for the light bulbs in series is
- and the power for the light bulbs in parallel is
- Hence, from the above equations, it is clear that in parallel circuits the bulbs will shine brightly.
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13. A dynamo which is said to generate electricity actually acts as a :
(a) Source of ions
(b) Source of electric charge
(c) Converter of energy
(d) Source of electrons
[U.P.P.C.S. (Mains) 2009]
Ans. (c) Converter of energy
- A dynamo, which is the same as an electrical generator, makes direct current with a part called a commutator.
- It is basically a tool that changes mechanical motion into electrical energy according to Faraday’s law.
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14. ‘Dynamo’ is a device, which converts :
(a) Chemical energy into electrical energy
(b) Electrical energy into mechanical energy
(c) Mechanical energy into electrical energy
(d) Electrical energy into chemical energy
[U.P. P.C.S. (Pre) 2016, 39th B.P.S.C. (Pre) 1994, U.P.P.C.S. ( Pre) 1993, U.P.P.C.S. ( Pre) 1992]
Ans. (c) Mechanical energy into electrical energy
- A dynamo is a machine that produces electricity from mechanical energy. ‘
- It uses a commutator to make direct current.
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15. Dynamo is a machine which is used for –
(a) Conversion of high voltage to low voltage
(b) Conversion of electrical energy to mechanical energy
(c) Conversion of mechanical energy to electrical energy
(d) Conversion of low voltage to high voltage
[U.P.P.C.S. (Mains) 2012, R.A.S./R.T.S.(Pre) 2012]
Ans. (c) Conversion of mechanical energy to electrical energy
- A dynamo is a machine that changes mechanical energy into electrical energy. It uses a commutator to make direct current.
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16. Turbines and Dynamos are used to convert which energy to electrical energy?
(a) Chemical energy
(b) Solar energy
(c) Mechanical energy
(d) Magnetic energy
[44th B.P.S.C. (Pre) 2000]
Ans. (c) Mechanical energy
- A dynamo converts mechanical energy into electrical energy.
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17. When electrical energy is converted into motion
(a) There is no heat loss
(b) Heat loss is 50 percent
(c) Heat loss is 30 percent
(d) Heat loss is 80 percent
[47th B.P.S.C. (Pre) 2005]
Ans. (a) There is no heat loss
- When electrical energy is converted into motion, there is no heat loss.
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18. A device which converts electrical energy into mechanical energy is –
(a) Dynamo
(b) Transformer
(c) Electric motor
(d) Inductor
[U.P.P.C.S. (Mains) 2007, Uttarakhand P.C.S. (Pre) 2005]
Ans. (c) Electric motor
- Electric motors are machines that take electricity and turn it into movement.
- They use wires that spin around when a magnetic field or electricity is applied.
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19. In electrical motor :
(a) heat is converted into electrical energy
(b) electrical energy is converted into heat
(c) electrical energy is converted into mechanical energy
(d) mechanical energy is converted into electrical energy
(e) None of the above / More than one of the above
[64th B.P.S.C. (Pre) 2018]
Ans. (c) electrical energy is converted into mechanical energy
- An electric motor is a machine that changes electricity into movement.
- It has two parts that move, the rotor and the stator, and two parts that do not move, the magnets and the armature.
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20. The device which works on the principle of electromagnetic induction is
(a) Ammeter
(b) Voltmeter
(c) Dynamo
(d) Electric motor
[U.P. R.O./A.R.O. (Pre) 2017]
Ans. (c) & (d) Dynamo & Electric motor
- The Dynamo and Electric motor are both machines that use electromagnetic induction to turn energy into different forms.
- The Dynamo changes mechanical energy into electricity and the Electric motor changes electricity into mechanical energy.
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21. A device which converts chemical energy into electrical energy is called –
(a) Battery
(b) Motor
(c) Generator
(d) Moving coil meter
[R.A.S./R.T.S. (Pre) 2013]
Ans. (a) Battery
- A battery is a device made up of cells that change stored chemical energy into electrical energy.
- There are several types of batteries, and all of them contain a positive electrode, negative electrode, and electrolyte.
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22. Electric motors operating at low voltages tend to burn out because –
(a) They draw more current which is inversely proportional to the voltage.
(b) They draw more current which is inversely proportional to the square root of the voltage.
(c) They draw heat proportional to v2
(d) Low voltage sets in electrical discharge.
[U.P.P.C.S. (Pre) 2008]
Ans. (a) They draw more current which is inversely proportional to the voltage
- Electric motors that run on low power will often break down because they take in more electricity which is the opposite of the voltage.
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23. Faraday constant :
(a) depends on the amount of the electrolyte
(b) depends on the current passed in the electrolyte
(c) depends on the volume of the solvent in which the electrolyte is dissolved
(d) is a universal constant
(e) None of the above / More than one of the above
[66th B.P.S.C. (Pre) 2020]
Ans. (d) is a universal constant
- The Faraday constant, named after the English scientist Michael Faraday, is a universal number that stands for how much electric charge there is in a mole of electrons.
- It is given the symbol ‘F’ and has the value of 96485.332123 C.mol–1.
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24. Consider the following statements regarding a motor car battery –
1. The voltage is usually 12 V.
2. The electrolyte used is hydrochloric acid.
3. Electrodes are lead and copper.
4. Capacity is expressed in ampere-hour.
Which of the above statements is correct?
(a) 1 and 2
(b) 2 and 3
(c) 3 and 4
(d) 1 and 4
[I.A.S. (Pre) 1999]
Ans. (d) 1 and 4
- A motor car battery typically has six cells of 2 volts each, which add up to a total of 12 volts.
- The capacity of the battery is measured in ampere-hours, which is the amount of electrical charge that flows when a current of 1 ampere is used for one hour.
- The electrolyte in the battery is a mixture of 35% sulfuric acid and 65% water.
- The electrodes in the battery are made of lead and lead dioxide.
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25. Nickel-Cadmium (Ni-Cd) battery is used in :
(a) Calculator
(b) Cordless electronic appliances
(c) Transistors
(d) All of the above
[Uttarakhand P.C.S. (Pre) 2016]
Ans. (d) All of the above
- The nickel-cadmium battery is a type of rechargeable battery.
- It uses nickel oxide hydroxide and metallic cadmium as its electrodes, and potassium hydroxide as an alkaline electrolyte.
- It is used in many devices, such as calculators, cordless electronic appliances, transistors, portable power tools
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26. Which of the following metals is used as filament in lighting bulbs?
(a) Iron
(b) Molybdenum
(c) Silver
(d) Tungsten
[44th B.P.S.C. (Pre) 2000]
Ans. (d) Tungsten
- In 1781, scientists Carl Wilhelm Scheele and Torbern Bergman thought it might be possible to make a new metal from tungsten acid.
- Two years later, Juan Jose and Fausto Elhuyar were the first to make tungsten by reducing the acid with charcoal. Because of this, they are given credit for discovering the element.
- It has a melting point of 3422 degrees Celsius and a boiling point of 5555 degrees Celsius.
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27. The filament of an electric bulb is made of –
(a) Magnesium
(b) Iron
(c) Nichrome
(d) Tungsten
[U.P.P.C.S (Pre) 2011, U.P.P.C.S. (Pre) 2005, U.P.P.C.S. (Pre) 1990]
Ans. (d) Tungsten
- The lightbulb filament is made of tungsten, a metal that conducts electricity well and can withstand very high temperatures.
- It has the highest melting point, lowest vapor pressure, and strongest tensile strength of any metal.
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28. The filament of an electric bulb is made of :
(a) Tungsten
(b) Nichrome
(c) Lead
(d) Aluminium
[Uttarakhand P.C.S. (Pre) 2012]
Ans. (a) Tungsten
- The filament of a bulb is made up of tungsten. Tungsten can become white hot and emit white light for a long time.
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29. Consider the following statements : An ordinary light bulb has a rather short life because the:
1. Filament wire is not uniform.
2. Bulb cannot be evacuated completely.
3. Wires supporting the filament melt at high temperatures.
Which of the above statements is correct?
(a) 1 and 3
(b) 2 and 3
(c) 1 and 2
(d) 1, 2 and 3
[I.A.S. (Pre) 1999]
Ans. (d) 1, 2 and 3
- An ordinary light bulb has a rather short life because the:-
- (1) Filament wire is not uniform (2) bulb cannot be evacuated completely and (3) wires supporting the flament melt at high temperature.
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30. The temperature of the filament of lighted electric bulb is generally :
(a) 100oC to 500oC
(b) 1000oC to 1500oC
(c) 2000oC to 2500oC
(d) 3000oC to 3500oC
[R.A.S./R.T.S.(Pre) 2007]
Ans. (c) 2000oC to 2500oC
- Tungsten is the material used in the filament of a light bulb.
- When an electric current is applied, the temperature of the filament rises to between 1500 and 2500 degrees Celsius.
- Usually, only 5-10% of the electrical energy is converted into light.
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31. Lightning can even burn a tree because it contains tremendous amount of
(a) Heat energy
(b) Electric energy
(c) Chemical energy
(d) Nuclear energy
[M.P.P.C.S. (Pre) 2017]
Ans. (b) Electric energy
- Lightning has so much electrical energy that it has the power to burn down a tree.
- Lightning is created when an electrical imbalance occurs between clouds and the ground, or within the clouds.
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32. Consider the following statements :
Assertion (A): Lightning conductors prevent buildings from damages in the event of lightning strike.
Reason (R): The electric charge conduct to ground through the wire, instead of passing through the structure.
Select the correct answer using the codes given below:
Code :
(a) Both (A) and (R) are correct, and (R) is the correct explanation of (A).
(b) Both (A) and (R) are correct, but (R) is not the correct explanation of (A).
(c) (A) is correct but (R) is wrong.
(d) (A) is correct but (R) is wrong.
[Uttarakhand P.C.S.(Mains) 2002, U.P.P.C.S. (Pre) 1999]
Ans. (a) Both (A) and (R) are correct, and (R) is the correct explanation of (A)
- A lightning conductor is a metal rod that is connected to the top of a tall building and wired to the ground.
- It is designed to protect the structure if lightning strikes by directing the electricity away from the building and into the ground.
- This will help to keep the structure safe.
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33. In a three-pin electrical plug longest pin should be connected to
(a) Ground terminal
(b) Live terminal
(c) Neutral terminal
(d) Any terminal
[U.P.P.C.S. (Pre) 2007]
Ans. (a) Ground terminal
- A three-pin plug has three ends – live, neutral, and earth.
- The earth pin is longer than the other two pins, so it will be the first to connect and the last to disconnect, which makes the plug safer to use.
- This pin also makes it easier for electricity to flow away in case of a fault.
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34. In electric apparatus ‘earth’ is used:
(a) To reduce the expenditure
(b) Because the apparatus used 3-phase
(c) For safety
(d) In the form of fuse
[U.P.P.C.S. (Pre) 2002]
Ans. (c) For safety
- The Earth wire helps to take away any extra electricity from electrical devices and send it through the ground.
- This helps to protect any appliances from getting damaged by the excess electricity.
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35. The electric current does not flow between two properly connected charged bodies if they are having
(a) Same charge
(b) Same capacity
(c) Same resistivity
(d) Same potential
[U.P.P.S.C. (R.I.) 2014]
Ans. (d) Same potential
- Ohm’s law states that when there is a voltage difference between two points in a circuit, a current will flow through a resistor.
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36. A fuse is used in main electric supply as a safety device. Which one of the following statements about the fuse is correct?
(a) It is connected in parallel with the main switch
(b) It is made mainly from silver alloys
(c) It must have a low melting point
(d) It must have a very high resistance
[I.A.S. (Pre) 1998]
Ans. (c) It must have a low melting point
- An electric fuse is a device used to stop electrical damage.
- It has a wire made of metal or alloy that melts when too much current flows through it.
- This breaks the circuit, and stops the current from flowing. This prevents any further damage.
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37. The principle of fuse is
(a) Chemical effect of electricity
(b) Mechanical effect of electricity
(c) Heating effect of electricity
(d) Magnetic effects of electricity
[43rd B.P.S.C. (Pre) 1999]
Ans. (c) Heating effect of electricity
- A fuse is an electrical device that works by using the heat generated by an electric current.
- When the current is higher than the allowed level, the heat causes the fuse to melt and this stops the current from flowing.
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38. A fuse wire is characterized by:
(a) Low resistance and high melting point.
(b) Low resistance and low melting point.
(c) High resistance and low melting point.
(d) High resistance and high melting point.
[U.P. P.C.S. (Pre) 1993]
Ans. (c) High resistance and low melting point
- Fuse is a thin wire with a special property of melting at a low temperature when too much current flows through it.
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39. Fuse wire used for safety of household have :
(a) Low melting point
(b) High melting point
(c) High resistance
(d) Low resistance.
[R.A.S./R.T.S. (Pre) 1997-98]
Ans. (a) & (c) Low melting point & High resistance
- Fuse wires are put in homes as a safety measure.
- They have a low melting point and are made of metals like tin, lead, or zinc.
- They act as a safety device to protect against too much electricity in a circuit.
- If too much electricity flows, the wire melts and breaks the circuit, keeping the wiring and appliance from getting damaged.
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40. The filament of a halogen lamp is an alloy of –
(a) Tungsten and iodine
(b) Tungsten and bromine
(c) Tungsten and sodium
(d) Molybdenum and sodium
[R.A.S./R.T.S.(Pre) 1999]
Ans. (c) Tungsten and sodium
- The inside part of a halogen lamp is made of a combination of tungsten and sodium.
- This causes the light to be a yellow color.
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41. Assertion (A): The temperature of a metal wire rises when an electric current is passed through it.
Reason (R): Collision of metal atoms with each other releases heat energy.
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) 1998]
Ans. (c) (A) is true but (R) is false
- When electricity travels through a wire, the electrons hit the atoms of the material the wire is made of.
- This gives the atoms energy, making the conductor get hot.
- Assertion A is true, but the reason for it being true (R) is not correct.
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42. Domestic electrical wiring is basically a :
(a) Series connection
(b) Parallel connection
(c) Combination of series and parallel connections
(d) Series connection within each room and parallel connection elsewhere
[I.A.S. (Pre) 1996]
Ans. (b) Parallel connection
- In a domestic electrical wiring system, each part is connected together in a parallel arrangement.
- This means that each branch in the circuit receives the same amount of electricity.
- If one of the bulbs in the circuit is taken out, the electricity will still flow through the other parts and the other bulbs will stay lit.
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43. A wire with black insulation during electric supply is–
(a) Live wire
(b) Earth wire
(c) Neutral wire
(d) Fuse wire
(e) None of the above
[Chhattisgarh P.C.S. (Pre) 2014]
Ans. (c) Neutral wire
- The electricity to our home is sent through three different wires: a live wire, a neutral wire, and an earth wire.
- To keep things organized, we use a color coding system for the insulation on these wires.
- The live wire is red, the neutral wire is black, and the earth wire is wrapped in green plastic.
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44. What is the order of magnitude of electric resistance of the human body (dry)?
(a) 102 ohm
(b) 104 ohm
(c) 106 ohm
(d) 108 ohm
[I.A.S. (Pre) 2005]
Ans. (b) 104 ohm
- The electric resistance of a human body when dry is usually around 10,000 ohms, but can be as high as 100,000 ohms or more.
- If the skin is wet or broken, the resistance of the body can drop to 1,000 ohms or lower.
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45. Full form of C.F.L. is –
(a) Compact Fluorescent Lamp
(b) Centrally Fixed Lamp
(c) Chemical Fluorescent Lamp
(d) Condensed Fluorescent Lamp
[U.P.P.C.S. (Mains) 2015]
Ans. (a) Compact Fluorescent Lamp
- C.F.L. stands for Compact Fluorescent Lamp. It uses much less energy than regular light bulbs, saving 75% of electricity.
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46. Light Emitting Diode (LED) work on principle of :
(a) Laser
(b) Thermionic emission
(c) Photoelectric code
(d) Electroluminescence
[Jharkhand P.C.S. (Pre) 2021]
Ans. (d) Electroluminescence
- LEDs work by Electroluminescence. This is when a material produces light when electricity or a strong electric field passes through it.
- It happens when electrons and holes in a semiconductor join together and release energy in the form of light.
- LEDs are made from semiconductors that let out light when electric current passes through them.
- Electrons and holes in the semiconductor combine and release energy as light.
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47. Assertion (A): Light Emitting Diode (LED) lamps offer longer service life as compared to Compact Fluorescent Lamps (CFL).
Reason (R): Light Light-emitting diode (LED) lamps are more energy efficient as compared to Compact Fluorescent Lamps (CFL).
Select the correct answer using the codes given below:
(a) Both (A) and (R) are true, and (R) explains (A).
(b) Both (A) and (R) are true, but (R) does not explains (A).
(c) (A) is true, and (R) is false.
(d) (A) is false, and (R) is true.
[R.A.S./R.T.S.(Pre) 2013]
Ans. (a) Both (A) and (R) are true, and (R) explains (A).
- Gallium arsenide is used in LED lamps to turn electricity into light.
- It lasts longer than CFL lamps because it uses less energy.
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48. What is the difference between a CFL and an LED Lamp?
1. To produce light, a CFL uses mercury vapour and phosphor while an LED lamp uses semi-conductor material.
2. The average life span of a CFL is much longer than of an LED lamp.
3. A CFL is less energy-efficient as compared to an LED lamp.
Which of the statements given above is/are correct?
(a) 1 only
(b) 2 and 3
(c) 1 and 3
(d) 1, 2 and 3
[I.A.S. (Pre) 2011]
Ans. (c) 1 and 3
- CFLs use a combination of mercury vapour and phosphor to produce light.
- Electricity causes the gases to become excited, creating invisible ultraviolet light.
- The UV light then interacts with the white phosphor coating inside the bulb, causing it to glow and emit white light.
- LEDs use a semi-conductor material to create light. CFLs last between 6,000-10,000 hours, while LEDs can last up to 50,000 hours. LEDs are also more energy efficient than CFLs.
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49. With reference to street lighting, how do sodium lamps differ from LED lamps?
1. Sodium lamps produce light in 360 degrees but it is not so in the case of LED lamps.
2. As street lights, sodium lamps have a longer life span than LED lamps.
3. The spectrum of visible light from sodium lamps is almost monochromatic while LED lamps offer significant colour advantages in street lighting.
Select the correct answer using the code given below.
(a) 3 only
(b) 2 only
(c) 1 and 3 only
(d) 1, 2 and 3
[I.A.S. (Pre) 2021]
Ans. (c) 1 and 3 only
- Sodium lamps produce light in all directions, which means a lot of light is wasted by having to be redirected or reflected to the area being lit.
- LED lamps, on the other hand, emit light in only a 180 degree area, so there is less wasted light.
- LEDs also have a much longer lifespan than sodium lamps and they produce less wasteful heat.
- Plus, they have a much better colour rendering index than sodium lamps, so objects illuminated by them appear coloured rather than shadowy black.
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50. What gases are filled in fluorescent tube?
(a) Neon
(b) Sodium
(c) Mercury
(d) Mercury and neon
[U.P. P.C.S. (Pre) 1990]
Ans. (d) Mercury and neon
- Fluorescent lamps contain gases like Mercury and other gases like Argon, Neon, Xenon, and Krypton, all at a low pressure.
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51. In comparison to an electric bulb, a fluorescent tube is preferred because –
(a) It has greater external outer surface to radiate/emit the light.
(b) There is no efect of voltage fuctuation on it.
(c) In the tube, electric energy almost converted into light energy.
(d) None of these.
[U.P. P.C.S. (Pre) 2009]
Ans. (d) None of these
- Electric bulbs are not as efficient as fluorescent tubes when it comes to converting electric energy into light energy.
- A 100 watt bulb only turns 5% of electric energy into light energy, while fluorescent tubes can turn approximately 22% of electric energy into light energy. Therefore, none of the statements are correct.
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52. How does the white light produce in the tube?
(a) by heating up the copper wire
(b) by heating up the filament
(c) by accelerating the atoms
(d) by oscillating the molecules
[47th B.P.S.C. (Pre) 2005]
Ans. (d) by oscillating the molecules
- A tube light or fluorescent lamp is a type of lighting that runs on electricity and mercury.
- The electricity makes the electrons move quickly between the poles and when they hit the mercury molecules they start to vibrate.
- This causes the mercury to ionize and make ultraviolet radiation.
- This radiation isn’t visible to the human eye, so the glass tube is coated with a fluorescent material that changes it into white light. (d) is the correct answer.
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53. What is the gas inside an electric bulb?
(a) Oxygen
(b) Air
(c) Carbon dioxide
(d) None of the above
[M.P.P.C.S. (Pre) 2000]
Ans. (d) None of the above
- Edison invented the electric bulb.
- It has a coiled filament made of tungsten metal, which is able to withstand high temperatures.
- To stop the metal from rusting, Nitrogen and Argon gases are used to fill the bulb instead of a vacuum.
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54. Fluorescent tubes are filled with a choke. The choke coil-
(a) Steps up the line voltage
(b) Steps down the line voltage
(c) Reduces current in the circuit
(d) Chokes low-frequency current
[I.A.S. (Pre) 2000]
Ans. (a) Steps up the line voltage
- The starter in the tube light increases the current and sends it to the choke coil.
- The choke coil increases the voltage of the current and sends it back to the tubelight, causing it to light up.
- After this process is finished, the choke is used to regulate the voltage, which helps protect the tubelight from any damage.
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55. With reference to the electric potential which of the following statements is/are correct?
1. It is a scalar quantity.
2. It is a vector quantity.
Select the correct answer using the codes given below.
Codes :
(a) Only 1
(b) Only 2
(c) Both 1 and 2
(d) Neither 1 nor 2
[U.P. P.C.S. (Pre) 2021]
Ans. (a) Only 1
- Electric potential is a type of measurement.
- It is the amount of effort that needs to be used to move one unit of electrical charge from one point to another point against an electric force.
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56. If potential difference and current flowing through a wire is increased twice each then electric power :
(a) Will remain unaffected
(b) Will increase four times
(c) Will increase two times
(d) Will decrease by half
(e) None of these
[Chhattisgarh P.C.S. (Pre) 2015]
Ans. (b) Will increase four times
- Power P = V × I
where V = Voltage
I = Current
- Since both the voltage and current are increased twice
⇒ P’ = (2. V) (2I)
P’ = 4 V . I = 4P
- Hence, the electric power will increase four times.
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57. Two wires have their lengths, diameters and resistivity all in the ratio of 1: 2. If the resistance of the thinner wire is 10 ohm, the resistance of the thicker wire is :
(a) 5 ohm
(b) 10 ohm
(c) 20 ohm
(d) 40 ohm
[I.A.S. (Pre) 2001]
Ans. (b) 10 ohm
- We know that,
R = ρ 1/a
R = resistance, = resistivity, l = length, a = Area.
- Let the ρ1, l1 and r1 is resistivity, length, and radius of the first wire respectively then, As per the question resistivity of the second wire ρ2 = 2 ρ1 Length of second wire l2 = 2 l1 The radius of the second wire r2 = 2r1
⇒ R1 = ρ1 l1/a1 = ρ1 l1/πr12
R2 = ρ2 l2/a2 = 2ρ1 × 2l1/πr12
= 4ρ1 l1/4πr12 = ρ1l1/πr12
R1/R2 = 1
- Since the resistance of thin wire R1 = 10Ω
- Therefore, the resistance of thicker wire R2 = 10Ω
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58. Small drops of the same size are charged to V volts each. If n such drops coalesce to form a single large drop, its potential will be :
(a) n2/3 V
(b) n1/3 V
(c) n V
(d) N–1 V
[U.P. Lower Sub. (Mains) 2015]
Ans. (a) n2/3 V
- Let the charge on every small drop = q
- Radius of every small drop = r
- Charge on large drop (Q) = nq
- Radius of large drop = R
- the total volume of n drops = volume of the large drop
n × 4/3 πr³
⇒ R = n1/3 × r
Now, V’/V = Q’C/qC’
= Q’/q × r/R
= nq × r/n1/3 × r
⇒ V’ = n2/3 ×V
⇒ So, the potential of large drop = n2/3 V
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59. Given below are two statements, one labelled as Assertion (A) and the other labelled as Reason (R).
Assertion (A): Transformer is useful for stepping up or stepping down voltages.
Reason (R): Transformer is a device used in D.C. circuits.
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) 1996]
Ans. (c) (A) is true but (R) is false
- A transformer is used to move electricity between two or more linked circuits using magnetism.
- It can turn high voltage into low voltage and vice versa.
- Transformers can only work with AC electricity, not DC.
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60. The transformer is used for
(a) Converting AC into DC
(b) Converting DC into AC
(c) To step-up DC voltages
(d) To step-up or step-down AC voltages
[U.P.P.C.S. (Pre) 2006]
Ans. (d) To step-up or step-down AC voltages
- A transformer is used to change the voltage of alternating current.
- It has two coils: a primary coil and a secondary coil.
- The alternating current runs through the primary coil which affects the potential in the secondary coil.
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61. Which of the following is the purpose for which a transformer is used?
(a) To convert AC into DC
(b) To convert DC into AC
(c) To step-up or step-down AC voltage
(d) To step up DC voltage
[U.P.P.C.S. (Mains) 2011]
Ans. (c) To step-up or step-down AC voltage
- A transformer is a tool used to transfer electrical power. It usually changes the voltage of the current without changing the frequency of the alternating current (AC).
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62. A mobile phone charger is –
(a) An inverter
(b) A UPS
(c) A step up transformer
(d) A step down transformer
[U.P.P.C.S. (Pre) 2017]
Ans. (d) A step down transformer
- A mobile phone charger converts the alternating current (AC) from your wall socket into direct current (DC).
- The charger takes the high voltage of 220 volts from the switchboard and turns it into a lower voltage of either 9 or 10 volts.
- To do this, it uses a step down transformer.
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63. Some pairs of devices and associated energy changes are given below :
(i) Electric generator – Mechanical to electrical
(ii) Electric motor – Electrical to mechanical
(iii) Diesel engine – Light to electrical
(iv) Solar cell – Chemical to mechanical
Which of the above pair/s is/are correctly matched?
(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii) and (iv)
(d) (iii) and (iv)
[R.A.S./R.T.S.(Pre) 2013]
Ans. (a) (i) and (ii)
- An electric generator is something that takes energy from outside sources and turns it into electricity.
- An electric motor takes electricity and turns it into movement.
- A diesel engine is a type of engine that uses heat from compressed air to start the fuel burning.
- Solar cells take energy from the sun and turn it into electricity.
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64. The basic difference between an AC generator and a DC generator is that –
(a) An AC generator has an electromagnet while a DC generator has a permanent magnet
(b) The AC generator has slip rings while the DC generator has a commutator
(c) DC generator will generate a higher voltage
(d) AC generator will generate a higher voltage
[Chhattisgarh P.C.S. (Pre) 2018]
Ans. (b) The AC generator has slip rings while the DC generator has a commutator
- The arm of an AC generator is linked to an outside circuit using slip rings.
- To reverse the alternating voltage in a DC generator, a commutator is used every half cycle.
- Therefore, an AC generator uses slip rings and a DC generator uses a commutator.
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65. Alternate current is not preferable –
(a) To charge storage battery
(b) To run/start a electric motor
(c) To transmit electric power
(d) To heat up electric toaster
[R.A.S./R.T.S. (Pre) 1994]
Ans. (a) To charge storage battery
- Batteries are charged using Direct Current (DC).
- A rectifier is used to change the Alternating Current (AC) into DC, so AC is not suitable for charging batteries.
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66. The device used for converting alternating current to direct current is called –
(a) Inverter
(b) Rectifier
(c) Transformer
(d) Transmitter
Chhattisgarh P.C.S. (Pre) 2008, U.P.P.C.S. (Pre) 2006
Ans. (b) Rectifier
- A rectifier is a tool that changes AC electricity into DC. An inverter does the opposite – it changes DC into AC.
- A transformer takes AC power from the power grid and converts it into different voltages for other electronic devices.
- Finally, a transmitter is a device that sends out radio waves and is used for radio, TV and other communication tools.
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67. Alternating current is converted to direct current –
(a) By Dynamo
(b) By Motor
(c) By Transformer
(d) By Rectifier
[U.P. U.D.A./L.D.A. (Spl) (Mains) 2010]
Ans. (d) By Rectifier
- A rectifier is a device that turns AC power into DC power.
- It uses P-N junction diodes to convert alternating electricity into direct current.
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68. Assertion (A): In India, electricity distribution companies calculate the consumption of electricity in kWh.
Reason (R): The electrical system in India works at a frequency of 60 Hz.
Code :
(a) both (A) and (R) are individually true, and (R) is the correct explanation of (A).
(b) both (A) are (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.
[M.P.P.C.S. (Pre) 2008]
Ans. (c) (A) is true, but (R) is false.
- In India, the power grid works at a fixed frequency of 50 Hz. A slight increase or decrease of 0.5 Hz is okay, but if it goes beyond that, the grid won’t work.
- Electricity consumption is measured in kWh (units), so statement (A) is correct but (R) is not.
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69. Which of the following options represents the consumption of power in ascending order–
(a) Television, fan, electronic press, electronic kettle
(b) Television, fan, electronic kettle, electronic press
(c) Fan, television, electronic press, electronic kettle
(d) Electronic press, electronic kettle, fan, television
[U.P.P.C.S. (Pre) 1992]
Ans. (c) Fan, television, electronic press, electronic kettle
- The makers of electronic items give each of them a power rating, which is the most amount of power they can take.
- The order of the items from lowest to highest power rating is fan, television, electronic press, and electronic kettle.
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70. The earth’s magnetic field is due to
(a) Currents circulating inside the core
(b) Presence of a huge magnet at is centre
(c) Moving charges in space outside
(d) None of the above
[U.P.P.C.S. (Mains) 2011]
Ans. (a) Currents circulating inside the core
- It is thought that the magnetic field of the earth is caused by electric currents in its core, made by hot air that is moving up from the center.
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71. What is the source of electrical energy in an artificial satellite ?
(a) Solar cells
(b) Mini nuclear reactor
(c) Dynamo
(d) Thermopile
[U.P.P.C.S. (Pre) 2014, 2006, 2000, M.P.P.C.S. (Pre) 2000]
Ans. (a) Solar cells
- Artificial satellites use solar cells to turn the energy from the sun into electricity.
- This is done through a process called the photovoltaic effect which produces voltage and electricity when exposed to light.
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72. Consider the following statements :
Assertion (A) :Space-based solar power (SBSP), it is suggested be made a national goal.
Reason (R) :Supply of SBSP is 99% uninterrupted throughout the year, besides the enormity of energy availability.
Select the correct answer using the codes given below :
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 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) 2010]
Ans. (a) Both A and R are true, and R is the correct explanation of A
- Space-based solar power (SBSP) is a way to collect energy from the sun in space and use it here on Earth.
- It is different from how we currently collect energy from the sun, since it is done with a satellite orbiting in space instead of on the ground.
- The power is sent to Earth using a special frequency of electromagnetic waves.
- Special devices called “rectenna” turn the waves into electricity, which is then used on the local electricity grid.
- This power is almost always available, except during huge storms. Former President Dr. APJ Abdul Kalam said that SBSP should be a national goal.
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73. With reference to technologies for solar power production, consider the following statements :
1. ‘Photovoltaics’ is a technology that generates electricity by direct conversion of light into electricity, while ‘Solar Thermal’ is a technology that utilizes the Sun’s rays to generate heat which is further used in electricity generation process.
2. Photovoltaics generates Alternating Current (AC), while Solar Thermal generates Direct Current (DC).
3. India has manufacturing base for Solar Thermal Technology, but not for Photovoltaics.
Which of the statements given above is/are correct?
(a) 1 only
(b) 2 and 3 only
(c) 1, 2 and 3
(d) None
[I.A.S. (Pre) 2014]
Ans. (a) 1 only
- Photovoltaics is a technology that turns light into electricity using special materials.
- Solar cells create direct current power from the sun. Solar Thermal Technology uses solar energy to create heat, which can then be used to produce electricity.
- In March 2013, the Indian government said that they had enough capacity to make 2000 MW of electricity using photovoltaic modules.
- This means that India has the necessary equipment for photovoltaic technology.
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74. With reference to solar water pumps, consider the following statements:
1. Solar power can be used for running surface pumps and not for submersible pumps.
2. Solar power can be used for running centrifugal pumps and not the ones with piston.
Which of the statement 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) 2020]
Ans. (d) Neither 1 nor 2
- Solar-powered pumps run on electricity created from sunlight, instead of electricity from the grid or diesel.
- This type of power can be used for surface pumps and submersible pumps, which can be used for irrigation and to get drinking water from underground sources.
- Some solar pumps use a centrifugal mechanism, while others are positive displacement pumps.
- Positive displacement pumps can be used for car washing, irrigation, spraying, fountains and garden water pumps. Both of the given statements are incorrect.
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75. Which one of the following elements is used in solar cells?
(a) Silicon
(b) Cerium
(c) Astatine
(d) Vanadium
[Uttarakhand P.C.S. (Pre) 2012]
Ans. (a) Silicon
- Solar cells are the parts of solar systems that take in the sun’s energy and turn it into electricity.
- These cells have materials with the ability to conduct electricity, and when they are hit with sunlight, their electrons become activated and start an electrical current.
- There are some different types of solar cells, but the two most common are those made of silicon and thin film.
- Most of the solar cells made today (90%) are made of silicon.
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76. Photovoltaic cells are :
(a) Solar cells
(b) Thermal cells
(c) Sulphur cells
(d) Molar cells
[U.P. P.C.S. (Pre) 2016]
Ans. (a) Solar cells
- The photovoltaic effect is what makes it possible to turn light energy into electricity.
- A photovoltaic cell is the part of the system that does this.
- Silicon is the most common material used to make these cells.
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77. Photovoltaic cells are related to :
(a) Nuclear Energy
(b) Geo Thermal Energy
(c) Solar Energy
(d) Wind Energy
[R.A.S./R.T.S. (Pre) 2016]
Ans. (c) Solar Energy
- A solar cell (also known as a photovoltaic cell) is a type of device that turns sunlight (or other types of light) into electricity without using any moving parts.
- Sunlight is made up of particles of energy called photons.
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