Question

The rest positions of the needles in a milliammeter and voltmeter not in use are as shown in Fig. A. When a student uses these in his experiment, the readings of the needles are in the positions shown in Fig. B. The corrected values of current and voltage in the experiment are



(1) 42 mA and 3.2 V
(2) 42 mA and 4.0 V
(3) 34 mA and 3.2 V
(4) 34 mA and 4.0 V

Answer 1

Number of divisions on the scale of milliammeter = 5

Least count of the milliammeter$=\frac{10\text{mA}}{5}=2\text{mA}$
Zero error$=-4\text{mA}$

Reading on the main scale = 38 mA

Correct reading = Main reading $-$ Zero error = 38 mA $-$ ($-$ 4 mA) = 42 mA


Number of divisions on the voltmeter scale = 5

Least count of the Voltmeter = $\frac{1\text{V}}{5}=0.2\text{V}$
Zero error = + 0.4 V

Reading on the main scale = 3.6 V

Correct reading = Main reading $-$ Zero error = 3.6 V $-$ (+ 0.4 V) = 3.2 V

Hence, the correct answer is option 4.