Question

Potentiometer wire of length $1$m is connected in series with $490\Omega$ resistance and $2$V battery. If $0.2$mV/cm is the potential gradient, then resistance of the potentiometer wire is?

• A. $4.9\Omega$
• B. $7.9\Omega$
• C. $5.9\Omega$
• D. $6.9\Omega$

Answer 1

The correct option is A $4.9\Omega$

$R_p$ is resistance of potentiometer.

Potential difference across potentiometer=potential gradient $\times$ length

$=0.2\times {10}^{-3}\times 100=0.02V$

Current in circuit$=I=\frac{E}{R+R_p}=\frac{2}{490+R_p}$

Potential difference across potentiometer=$I{R}_p$

$⟹\frac{2R_p}{490+R_p}=0.02$

$⟹1.98R_p=9.8$

$⟹R_p=4.9\Omega$

Answer-(A)