Question

A bar magnet having a magnetic moment of 2.0 × 10⁵ JT^-1, is placed along the direction of uniform magnetic field of magnitude B = 14 × 10^-5 T. The work done in rotating the magnet slowly through 60° from the direction of field is ______.

Options

• 14 J

• 8.4 J

• 4 J

• 1.4 J

Answer 1

A bar magnet having a magnetic moment of 2.0 × 10⁵ JT^-1, is placed along the direction of uniform magnetic field of magnitude B = 14 × 10^-5 T. The work done in rotating the magnet slowly through 60° from the direction of field is 14 J.

Explanation:

Work done is rotating a dipole for θ = θ₁ to θ = θ₂ is given by

W = MB(cos θ₁ - cos θ₂) = MB(cos 0° - cos 60°)

= `"MB"/2`

= `(2xx10^5xx14xx10^-5)/2`

= 14 J