CAIE A-Level Physics 10.3.3 Galvanometer Null Methods

Practise explaining how a galvanometer null method works and why zero deflection indicates balance, then interpreting the compared measurement.

Exam points

explain the role of a galvanometer in a null method and why zero deflection indicates balance
interpret a null-method circuit to identify the balance condition or the measurement being compared

[Maximum number: 1]

In the circuit shown, a battery of negligible internal resistance is connected in series with a pair of fixed resistors $\mathrm{R}_{1}$ and $\mathrm{R}_{2}$ .

Figure for Question 10.3.3—The use of a galvanometer in null methods question 1 — CAIE A-Level Physics AS

The circuit is to be used to test whether the electromotive force (e.m.f.) of a particular cell is 1.5 V . The cell is connected between terminals X and Y in parallel with $R_{2}$ and in series with a galvanometer.

Which statement about the test is correct?

Any non-zero reading on the galvanometer means the cell has an e.m.f. of 1.5 V .

The battery does not need to have an e.m.f. of 6.0 V .

The cell may be connected either way round between X and Y .

The galvanometer does not need a scale calibrated in amperes.

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10.3.3—The use of a galvanometer in null methods question 1