Question

In the experiment of calibration of voltmeter, a 1.1 volt standard cell gets balanced at 440 cm length of the wire. The balancing length corresponding to a potential difference between the ends of a resistance comes out to be 190 cm. A voltmeter shows 0.5 volt for this potential difference. The error in the reading of voltmeter will be

• A. 0.025 Volt
• B. 25 Volt
• C. 2.5 Volt
• D. 0.25 Volt

Answer 1

Answer: (A)

0.025 Volt

Given that,

The emf of cell is, $E=1.1V$

The balancing length for E is, $L=440cm$

The balancing length for resistance $R$ is, $l=190cm$

Let, $k$ be the potential gradient of experimental wire,

$k=\frac{E}{L}$

$k=\frac{1.1}{440}=0.0025$ Vm${}^{-1}$

The voltage across resistance $R$ is

$V_R=kl$

$V_R=0.0025\times 190$

$V_R=0.475V$

But, voltmeter shows 0.5 volt for voltage across resistance hence, the error in

the reading of voltmeter is

$0.5-V_R=0.5-0.475=0.025V$