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Class 12 Physics Chapter 3: Current Electricity Assertion-reason questions with answers

2 assertion-reason questions on Current Electricity, each with its answer and the reason, written from the NCERT chapter. For the CBSE board, JEE Main and NEET, which are set from the same NCERT chapter. Open a question's solution to check your working; then take the free test to find your next chapter. Each question gives an Assertion (A) and a Reason (R); choose how they stand to each other.

Question 1
Assertion (A): The emf of a cell equals the potential difference between its terminals when no current is drawn from it. Reason (R): The emf of a cell is the force with which the cell pushes charges round the circuit.
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Answer: (c) A is true, but R is false.

A is true: with I = 0, V = ε − Ir = ε. R is false: emf is not a force but a potential difference, the work done by the source per unit charge; the name is historical.

Question 2
Assertion (A): While a storage cell is being charged, the voltmeter across its terminals reads more than its emf. Reason (R): During charging, the current flows through the cell from its positive terminal to its negative terminal, so V = ε + Ir.
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Answer: (a) Both A and R are true, and R is the correct explanation of A.

Both true. Driving the current against the cell's emf adds the drop Ir to ε, so the terminal voltage V = ε + Ir exceeds ε; R explains A.

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