Which of the following statements are correct?
(A) Kirchhoff's loop rule represents energy conservation.
(B) Resistivity is a property of the material and depends on temperature.
(C) The electrical conductivity of the material does not depend on the material of the conductor and its temperature.
(D) The emf of a battery equals the potential difference between its terminals when the terminals are connected externally.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A) and (B) only
(A) Kirchhoff's loop rule represents energy conservation. — Correct. The sum of potential changes round a closed loop is zero because the electrostatic force is conservative: a charge that returns to its starting point has the same energy, so the loop rule expresses conservation of energy.
(B) Resistivity is a property of the material and depends on temperature. — Correct. Resistivity does not depend on the size or shape of the conductor; for metals it rises with temperature, \( \rho_T = \rho_0[1 + \alpha(T - T_0)] \).
(C) The electrical conductivity of the material does not depend on the material of the conductor and its temperature. — Incorrect. Conductivity \( \sigma = 1/\rho \), so it depends on the material and on temperature exactly as resistivity does.
(D) The emf of a battery equals the potential difference between its terminals when the terminals are connected externally. — Incorrect. When an external circuit is connected, a current \( I \) flows and the terminal voltage is \( V = E - Ir \), less than the emf. The emf equals the terminal voltage only on open circuit.