Which of the following statements are correct?
(A) The emf of a cell depends on the internal resistance of the cell.
(B) The emf of a cell depends on the external resistance of the circuit.
(C) It is easier to start a car engine on a warm day than on a cold day.
(D) The temperature coefficient of resistance (\( \propto \)) of carbon is negative.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (C) and (D) only
(A) The emf of a cell depends on the internal resistance of the cell. — Incorrect. The emf is fixed by the chemistry of the cell; the internal resistance only decides the terminal voltage \( V = \varepsilon - Ir \) when current flows.
(B) The emf of a cell depends on the external resistance of the circuit. — Incorrect. The external resistance changes the current drawn and the terminal voltage, not the emf.
(C) It is easier to start a car engine on a warm day than on a cold day. — Correct. The internal resistance of the battery rises when it is cold, so the battery delivers less current to the starter motor; on a warm day it is lower and the engine starts more easily.
(D) The temperature coefficient of resistance of carbon is negative. — Correct. Carbon (like semiconductors) is a material whose resistance falls as temperature rises, so its temperature coefficient is negative.
So the correct statements are (C) and (D), which is Option (2).