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A potentiometer wire of length 100cm has...

A potentiometer wire of length 100cm has a resistance of `10Omega`. It is connected in series with a resistance and a cell of emf 2V and of negligible interal resistance. A source of emf 10mV is balanced against a length of 40cm of the potentiometer wire. What is the value of external resistance?

Text Solution

Verified by Experts

40 cm of wire balance 10 m V
So, 100cm of wire will balance `(10 m V)/(40) xx 100 = 25 m V`
Let the external resistance be R.
The current in wire ` = (2)/(10+R)` and potential drop across wire ` = 25 m V = (2 xx 10)/(10+R)`
`R = 790 Omega`.
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