Question

A current balance is a device to measure magnetic forces. It is constructed from two parallel coils, each with an average radius of 12.5 cm. The lower coil rests on a balance; it has 20 turns and carries a constant current of 4.10 A. The upper coil, suspended 0.314 cm above the lower coil, has 50 turns and a current that can be varied. The reading of the balance changes as the magnetic force on the lower coil changes. What current is needed in the upper coil to exert a force of 1.30 N on the bottom coil

Answer 1

Answer: Current I = 6.34A

Explanation: Their will be attractive force if the currents in the coils are in the same direction, repulsive if in opposite directions.

The length to be considered is the circumference of the coils, 2π r , where r is the common radius.

In this question, currents will be I 1 I = n I and I 2 I = n I , where 1 n and 2 n are the numbers of turns in the coils and I is the common current.

Please find the attached file for the solution