Question

1. A student takes data on magnetic field as a function of distance for a permanent magnet and fit it to the equation B=A/d^3. They find the A parameter to be 3.87x10^-4. What is the value of the magnetic moment (μ)? Answer in A*m².

2. You have a loop of wire that you want to run a current through to produce an electromagnet. The radius of the loop is 9 mm and the magnetic moment you desire is 1.24 A*m². What current is required to produce this magnetic moment? Answer in Amps.

Answer 1

1.

The magnetic field at a point on the axis of a bar magnet is B = 10^-7 x 2 μ/d³

The given equation for magnetic field is B = A/d³

By comparing the two equations, A = 10^-7 x 2 μ

Magnetic moment, μ = A /10^-7 x 2 = 3.87 x 10^-4/ 10^-7 x 2 = 1.94 x 10³ Am²

Magnetic moment, μ = 1.94 x 10³ Am²

2.

Area of the loop, A = πr² = 3.14 x ( 9 x 10^-3)² = 2.54 x 10^-4 m²

Magnetic moment of a current loop, μ = I A

Current required, I = μ/A = 1.24/2.54 x 10^-4 = 4.88 x 10³ A

Current required, I = 4.88 x 10³ A