The ammeter reading in the figure below is 2A. Which observation is c…

The correct answer is Option (3) → 3

The meters are taken as ideal. The voltmeter is connected between A and B, across the cell, and so it is in parallel with the branch of the ammeter and R. The ideal ammeter has no potential drop, so the voltmeter reads the potential difference across R. By Ohm's law,

    \( \displaystyle V = IR \;\Rightarrow\; I = \frac{V}{R} \)

For each row, the current through R must equal the ammeter reading, 2 A:

    \( (1)\ \ I = 1/2 = 0.5\,\mathrm{A} \)
    \( (2)\ \ I = 12/5 = 2.4\,\mathrm{A} \)
    \( (3)\ \ I = 10/5 = 2\,\mathrm{A} \)
    \( (4)\ \ I = 8/3 \approx 2.67\,\mathrm{A} \)

Only row (3), 10 V across \( 5\,\Omega \), gives a current of 2 A.