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A potentiometer has a uniform wire of length 5 m and total resistance…
Question
A potentiometer has a uniform wire of length 5 m and total resistance 5 ohm. Its primary circuit consists of a driver cell of EMF 5 V (negligible internal resistance) in series with a 20 ohm resistor and the potentiometer wire. A test cell connected in the secondary is balanced (null point) at a length of 4 m along the wire. Find the EMF of the test cell, in volt.
✓ Verified answer: 0.8checked by our engine — not a guess
Step-by-step solution
Primary current I = EMF/(R_series + R_wire) = 5/(20 + 5) = 0.2 A.
Potential drop across the whole wire = I x R_wire = 0.2 x 5 = 1.0 V over 5 m, so the potential gradient = 1.0/5 = 0.2 V/m.
At balance the test EMF equals the potential across the balancing length: E = gradient x 4 = 0.2 x 4 = 0.8 V.
Final answer0.8
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