NCERT Class XII Chapter
Magnetism and Matter
Questions With Solutions
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Question : 7
Total: 25
A bar magnet of magnetic moment 1.5 J T – 1 lies aligned with the direction of a uniform magnetic field of 0.22 T.
(a) What is the amount of work required by an external torque to turn the magnet so as to align its magnetic moment : (i) normal to the field direction,
(ii) opposite to the field direction?
(b) What is the torque on the magnet in cases (i) and (ii)?
(a) What is the amount of work required by an external torque to turn the magnet so as to align its magnetic moment : (i) normal to the field direction,
(ii) opposite to the field direction?
(b) What is the torque on the magnet in cases (i) and (ii)?
Solution:
Soln. (a) Work required to turn the dipole, W = MB [cos θ i – cos θ f ]
(i)θ i = 0° and θ f = 90°
W = 1.5 × 0.22 [cos 0° – cos 90°] = 0.33 J
(ii)θ i = 0° and θ = 180°, W = 1.5 × 0.22 [cos 0° – cos 180°] = 0.66 J
(b) Torque when θ = 90°,τ 1 = MB sin 90° = 0.33 N m
Torque when θ = 180°,τ 2 = MB sin 180° = 0
(i)
W = 1.5 × 0.22 [cos 0° – cos 90°] = 0.33 J
(ii)
(b) Torque when θ = 90°,
Torque when θ = 180°,
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