Question

A bar magnet of length 14 cm is placed in the magnetic meridian with its north pole pointing towards the geographic north pole. A neutral point is obtained at a distance of 18 cm from the center of the magnet. If B_H = 0.4 G, the magnetic moment of the magnet is ______. (1 G = 10^–4T)

Options

• 28.80 J T^–1

• 2.880 J T^–1

• 2.880 × 10³ J T^–1

• 2.880 × 10² J T^–1

Answer 1

A bar magnet of length 14 cm is placed in the magnetic meridian with its north pole pointing towards the geographic north pole. A neutral point is obtained at a distance of 18 cm from the center of the magnet. If B_H = 0.4 G, the magnetic moment of the magnet is 2.880 J T^–1.

Explanation:

Given

Length of bar Magnet = 14 cm

B_H = 0.4G

From the diagram we observe,

B_H = 2B₁sinθ

`0.4 xx 10^-4 = 2[(mu_0m)/(4pir^2)][7/r]`

`0.4 xx 10^-4 = 2[(7 xx 10^-7m)/([7^2 + 18^2]^{3/2}) xx 10^4]`

∴ m = `(4xx10^-2xx(373)^{3/2})/14`

Magnetic Moment, M = m × `14/100`

⇒ `(4 xx 10^-2 xx (373)^{3/2})/14 [14/100]`

m = 2.880 J/T