In a potentiometer circuit used to measure an unknown resistance R, the balance (null) point is found at length PJ = 30 cm when a secondary cell of EMF Es = 10 V and internal resistance r = 1 ohm is used. When the secondary cell is replaced by another with Es = 5 V and r = 2 ohm, the balan

Question

In a potentiometer circuit used to measure an unknown resistance R, the balance (null) point is found at length PJ = 30 cm when a secondary cell of EMF Es = 10 V and internal resistance r = 1 ohm is used. When the secondary cell is replaced by another with Es = 5 V and r = 2 ohm, the balance point shifts to PJ = 10 cm. What is the value of R (in ohm)?

Accepted Answer

1 ohm. Dividing the two balance equations eliminates the potential gradient k and gives 3 = 2*(R+2)/(R+1), which solves to R = 1 ohm.

Solution

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