Question

The phenomenon observed when a material exhibits zero electrical resistance below a critical temperature is:

• A. Ferromagnetism
• B. Superconductivity
• C. Photovoltaic effect
• D. Thermionic emission

Hint:

Zero resistance + expelling magnetic fields = superconductivity. Watch for the keyword “critical temperature”!

Answer 1

The Correct Option is B

Step 1: Understand the term "zero electrical resistance".

• Electrical resistance opposes the flow of current.
• In most materials, resistance increases with temperature.
• But in certain materials, resistance drops to zero below a specific critical temperature.

Step 2: What is Superconductivity?

• Superconductivity is a quantum mechanical phenomenon.
• Below a critical temperature (\( T_c \)), a material enters a state where:
  • Electrical resistance becomes exactly zero.
  • Magnetic fields are expelled (Meissner effect).
• This allows current to flow indefinitely without energy loss.

Step 3: Why the other options are incorrect.

• (A) Ferromagnetism: Related to magnetic domain alignment, not zero resistance.
• (C) Photovoltaic effect: Involves conversion of light to electricity, not resistance behavior.
• (D) Thermionic emission: Refers to electron emission due to heat, unrelated to zero resistance.

Therefore, the phenomenon of zero electrical resistance below a critical temperature is called superconductivity.