Q 12-03-278JEE MainJEE Main 2019 (12 Apr, Shift 1)Medium
To verify Ohm's law, a student connects the voltmeter across the battery as shown in the figure. The measured voltage is plotted as a function of the current, and the following graph is obtained. If $V_0$ is almost zero, identify the correct statement:
Answer: (A) The emf of the battery is $1.5$ V and its internal resistance is $1.5\ \Omega$
The voltmeter reads the terminal voltage $V = \varepsilon - Ir$.
At $I = 0$: $V = \varepsilon = 1.5$ V. At $I = 1000$ mA $= 1$ A: $V = V_0 \approx 0$, so
$$r = \frac{\varepsilon - V_0}{I} = \frac{1.5}{1} = 1.5\ \Omega$$
The graph says nothing about R (the current was varied with the rheostat).
Solution by Sreeraj P, M.Sc Physics