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A Numerical problem from electricity

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In the given diagram,the cell and the ammeter, both have negligible resistance. the resisitors are identical. With switch K open , the ammeter reads 0.6 A. What will be the ammeter reading when the switch is closed?

-Mohit asked

Answer:

When the switch is open, the effective resistance is R/2, since the two resistances R each are in parallel.

Therefore, the pd, V = I x R/2 = 0.6 x R/2 = 0.3 R

When the key is closed, the effective resistance becomes R/3

Now the reading of the ammeter, I’ = V/(R/3) = 0.3R/(R/3)=0.9A

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