Conductivity Notes with PDF

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 Electrical Conductivity of Materials

1. Conductors (Metals)

• Order of Conductivity: Silver > Copper > Gold > Aluminium > Iron
• Practical Applications:
  • Copper is the most common material for electrical wires, despite silver being a better conductor, due to its lower cost and practical availability.
  • Copper is preferred over iron for applications like lightning conductors because it is a better conductor and is more resistant to oxidation (rusting).

2. Superconductors

• Definition: A material that exhibits two key properties:
  1. Zero Electrical Resistance: It can conduct electricity without any energy loss.
  2. Zero Permeability (Meissner Effect): It expels magnetic fields from its interior.
• Temperature Dependence:
  • Originally discovered at temperatures close to absolute zero (-273.15°C or 0 K).
  • High-Temperature Superconductors: A class of materials, often ceramic oxides containing elements like Mercury (Hg), Thallium (Tl), Barium (Ba), Calcium (Ca), and Copper oxide (CuO), that achieve superconductivity at higher (though still very cold) temperatures.
  • The highest recorded superconducting temperature is 288 K (15°C), achieved under extreme pressure using a compound of hydrogen, carbon, and sulphur.
• Significance: Achieving practical room-temperature superconductivity is a major scientific goal, as it would eliminate power loss during electrical transmission, saving enormous amounts of energy.

3. Semiconductors

• General Properties:
  • Their electrical conductivity is between that of conductors and insulators.
  • Conduction occurs through the movement of both electrons (negative charge) and holes (positive charge carriers).
  • They have a negative temperature coefficient of resistance, meaning their resistance decreases when temperature increases. This is because heating provides energy, freeing more electrons and creating more holes, thereby increasing conductivity.
  • At absolute zero (0 K), a semiconductor has infinite resistance and acts as a perfect insulator because no electrons have enough energy to conduct current.
• Common Materials:
  • The most important elemental semiconductors are Silicon (Si) and Germanium (Ge).
  • Silicon is the most widely used material for transistors and electronic devices because it can withstand higher temperatures than germanium.
  • Germanium (which can be recovered from burnt coal, or Jhama) was a crucial material in the development of early transistors.

Know More About Conductivity:

• Conductivity – Old Year Questions
• Conductivity One Liner Questions & Answers