The circuit shown has a 10 V cell, 400 Ω series resistor, a resistor R and a 2 V cell connected through an ideal galvanometer G. G shows zero deflection. Determine R. [Image]
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The circuit shown has a 10 V cell, 400 Ω series resistor, a resistor R and a 2 V cell connected through an ideal galvanometer G. G shows zero deflection. Determine R. [Image]

G1 Physics · Accepted Answer

Step 1: With zero galvanometer deflection, there is no current through G; therefore junction potential at G's left terminal equals +2 V of the right cell. Step 2: From 10 V supply to the 2 V junction, the 400 Ω series resistor has 8 V across it. Step 3: Current through it and through R is I = 8/400 = 0.020 A. Step 4: R = 2/0.020 = 100 Ω. Final answer: (A) 100 Ω.