Question

A $1\Omega$ resistance is in series with an ammeter which is balanced by 75 cm of potentiometer wire. A standard cell of 1.02 V is balanced by 50 cm. The ammeter shows a reading of 1.5A. The error in the ammeter reading

• A. 0.002 A
• B. 0.03 A
• C. 1.01 A
• D. no error

Answer 1

The correct option is B 0.03 A

$ip=\frac{V}{l}=\frac{1.02}{50}$
Voltage across ammeter = $\frac{V}{l}{l}_1$
$=\frac{1.02}{50}\times 75=\frac{1.02}{2}\times 3=0.51\times 3$
The true current $I_A^1=\frac{V_A}{R}=\frac{1.53}{1}{I}_A^1=1.53AError=I_A^1-I_A=1.53-1.5=0.03A$