A cell of emf 90 V is connected across series combination of two resistors each of 100 $$\Omega$$ resistance. A voltmeter of resistance 400 $$\Omega$$ is used to measure the potential difference across each resistor. The reading of the voltmeter will be:

When the voltmeter ($$R_v = 400\ \Omega$$) is connected across one of the $$100\ \Omega$$ resistors, they form a parallel combination: $$R_p = \frac{100 \times 400}{100 + 400} = \frac{40000}{500} = 80\ \Omega$$

$$R_{\text{total}} = R_p + 100 = 80 + 100 = 180\ \Omega$$

$$I = \frac{V_{\text{total}}}{R_{\text{total}}} = \frac{90\text{ V}}{180\ \Omega} = 0.5\text{ A}$$

$$V_{\text{reading}} = I \times R_p = 0.5\text{ A} \times 80\ \Omega = 40\text{ V}$$