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A potentiometer wire of length 10m and r...

A potentiometer wire of length 10m and resistances `20 Omega` is connected in series with a 15V battery and a external resistance `40 Omega`. A secondary cell of emf E in the secondary circuit is balanced by 240 cm long potentiometer wire. The emf E of the cell is

A

2.4V

B

1.2V

C

2.0V

D

3V

Text Solution

Verified by Experts

The correct Answer is:
B
Total resistance
or R=20+40
`R=60 Omega`
Given: v=15 volt
Current `I=V/R=15/60`
I=0.25 A
potential gradient `=V/l`
`=(20 times 0.25)/10`
`=0.5 Vm^-1`
Potential difference across 240 cm
`E=0.5 times 2.4`
`E=1.2 V`
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