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JEE MainPhysicsCurrent Electricity

A circuit contains a 24 V battery and a 56 resistor connected in series with an ammeter. The ammeter consists of a 20 galvanometer coil and an unknown shunt resistor. If the ammeter reads 400 mA , the resistance of the shunt is .

Correct answer

5

Step-by-step solution

Total current in the circuit, I = 400 mA = 0.4 A Let the total resistance of the circuit be R_ total . Using Ohm's law: R_ total = V I = 24 0.4 = 60 The total resistance is the sum of the series resistor and the equivalent resistance of the ammeter ( R_A ): R_ total = R_ ext + R_A 60 = 56 + R_A R_A = 4 The ammeter consists of a galvanometer coil ( R_g = 20 ) and a shunt ( S ) in parallel. Its equivalent resistance is: R_A = R_g S R_g + S 4 = 20 S 20 + S 80 + 4S = 20S 16S = 80 S = 5 Answer: 5

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