Question

A wire PQ is 100cm long. When PR= 30cm, no deflection in the galvanometer, then value of resistance S is?

Answer 1

Answer: 70 ohms

Explanation: L = PR = 30cm

                      RQ = 100 - PQ = 100 -L = 70 cm

                      r = 30 0hm

from meter bridge ,

PR / RQ = R /S

L / (100 - L ) = 30 / S

=> 30 / 70 = 30 / S

=> S = 70 ohms

 

Answer 2

Given:

A wire PQ is 100 cm long. When PR is 30 cm long , there is no deflection in the galvanometer.

To find:

Value of resistance S

Calculation:

This is a case of Balanced Wheatstone Bridge in which the adjacent resistances are in ratio such that no current flows through the galvanometer.

$\therefore \: \dfrac{30}{S} = \dfrac{PR}{RQ}$

$= > \: \dfrac{30}{S} = \dfrac{30}{100 - 30}$

$= > \: \dfrac{30}{S} = \dfrac{30}{70}$

$= > \: \dfrac{1}{S} = \dfrac{1}{70}$

$= > \: S = 70 \: ohm$

So final answer is :

Value of S resistance is 70 ohm