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12th Physics 2018 Set1 Delhi Board Paper Solution

Question 7

In a potentiometer arrangement for determining the emf of the cell, the balance point of the cell in open circuit is 350 cm. When a resistance of 9 Ω is used in the external circuit of the cell, the balance point shifts to 300 cm. Determine the internal resistance of the cell.

Answer

The balance point fo the cell in ofen circuit , l1 = 350cm

After applying resistance, balance point l = 300cm

Resistance in internal circuit  = 9 Ω

Internal resistance can be calculated by relation below:

r  = (l1/l2   - 1) x R  

r  = (350/300  -  1) x 9 

r  = 50/300 x 9  = 3/2  = 1.5 Ω

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