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Magnetism And Matter

Question
CBSEENPH12037742

A magnetic dipole is under the influence of two magnetic fields. The angle between the field directions is 60° and one of the fields has a magnitude of 1.2 x 10–2 tesla. If the dipole comes to stable equilibrium at an angle of 15° with this field, what is the magnitude of the other field ?

Solution

Given, a magnetic dipole is under the influence of two magnetic fields.
Angle between the field direction, θ = 60°
Magnitude of one field, B1 = 1.2 x 10–2 T
Angle at which the dipole comes to stable equilibrium, θ1 = 15°
Therefore, θ2 = 60° – 15° = 45°. 

In equilibrium, torques due to two fields must balance each other. 

i.e.,    τ1 = τ2
M B1 sin θ1 = MB2 sin θ

B2 = B1 sin θ1sin θ2     = 1.2 × 10-2 sin 45°sin 45°     = 1.2 × 10-2 × 0.25880.7071    = 4.4 × 10-3 T 

which is the required magnitude of the other field. 

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