In the experiment of calibration of voltmeter, a standard cell of e.m.f. 1.1 volt is balanced against 440 cm of potential wire. The potential difference across the ends of resistance is found to balance against 220 cm of the wire. The corresponding reading of voltmeter is 0.5 volt. The error in the reading of volmeter will be:

In a potentiometer, potential difference is proportional to balancing length.

First, find potential gradient:

$$k=\frac{1.1}{440}=0.0025\text{ V/cm}$$

Now for 220 cm:

$$V_{\text{true}}=k\times220=0.0025\times220=0.55\text{ V}$$

So actual voltage = 0.55 V

Given voltmeter reading = 0.5 V

Now error:

$$V\text{Error}=V_{\text{measured}}-V_{\text{true}}=0.5-0.55=-0.05\text{}$$

Negative sign means the voltmeter is reading less.

$$Finalanswer:\text{Error}=-0.05\text{ V}$$