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Current Electricity

Question
CBSEENPH12038972

Describe briefly, with the help of a circuit diagram, how a potentiometer is used to determine the internal resistance of a cell.

Solution

Potentiometer can be used to measure the internal resistance of the cell.
 

A cell of emf E is connected across the resistance box through key K1.

When key K1 is opened galvanometer shows deflection at the balancing length l1.

So, E = kError converting from MathML to accessible text. 
If both keys are closed, then balancing point is obtained at length l2 (l2 < l1).
So, V = kError converting from MathML to accessible text.
Now, using the relation, 
straight r space space equals straight R space open parentheses straight E over straight V space minus space 1 close parentheses
Therefore, we have
Error converting from MathML to accessible text.

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