Question

A $2\Omega$ resistor is connected in series with $R\Omega$ resistor. This combination is connected across a cell. When the potential difference across $2\Omega$ resistor is balanced on potentiometer wire, null point is obtained at length of 300cm. When the same procedure is repeated for $R\Omega$ resistor, null point is obtained at length 350cm, value of R is:

• A. 5
• B. 3.33
• C. 4.6
• D. 2.83

Answer 1

Answer: (D)

2.83

For only $R=2\Omega$

Balance Length $L=300cm$

For $R\Omega$ resistance in series

$R_{eq}=(2+R)\Omega$

Balance length $L=350cm$

From the potentiometer principal,

$\frac{R}{R_{eq}}=\frac{L}{l}$

$⟹\frac{2}{2+R}=\frac{300}{350}$

$2=0.85(2+R)$

$2=1.7+0.85R$

$0.3=0.85R$

$R=2.8\Omega$