JEE Main | 2018Current Electricity and Electrical InstrumentHard

Question

In a potentiometer experiment, it is found that no current passes through the galvanometer when the terminals of the cell are connected across 52 cm of the potentiometer wire. If the cell is shunted by a resistance of 5Ω, a balance is found when the cell is connected across 40 cm of the wire. Find the internal resistance of the cell.

Options

A.

1.5 Ω

B.

2 Ω

C.

2.5 Ω

D.

1 Ω

Solution

without shunting condition :

Es = 52 ×x ...(1)
when balanced
where, x = potential gradient of wire.
with shunting condition

On balancing
Es-Es(r+R)r=40 × x   ....(2)
On solving :
(1)(2)⇒11-rr+R=5240  ∴ r = 1.5Ω

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