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Question:
A closely wound solenoid of 2000 turns and area of cross-section 1.6 x 10-4 m2, carrying a current of 4.0 A, is suspended through its centre allowing it to turn in a horizontal plane. (a) What is the magnetic moment associated with the solenoid? (b) What is the force and torque on the solenoid if a uniform horizontal magnetic field of 7.5 x 10-2 T is set up at an angle of 30degree with the axis of the solenoid?
Answer:

Number of turns on the solenoid, n = 2000

Area of cross-section of the solenoid, A= image050 NCERT Solutions class-12 physics Magnetism and Matter

Current in the solenoid, I= 4 A

(a)The magnetic moment along the axis of the solenoid is calculated as:

M= nAI

= image051 NCERT Solutions class-12 physics Magnetism and Matter

= 1.28 Aimage052 NCERT Solutions class-12 physics Magnetism and Matter

(b)Magnetic field, B =image053 NCERT Solutions class-12 physics Magnetism and Matter

Angle between the magnetic field and the axis of the solenoid, θ= 30°

Torque, image029 NCERT Solutions class-12 physics Magnetism and Matter

image054 NCERT Solutions class-12 physics Magnetism and Matter

image055 NCERT Solutions class-12 physics Magnetism and Matter

Since the magnetic field is uniform, the force on the solenoid is zero. The torque on the solenoid is image056 NCERT Solutions class-12 physics Magnetism and Matters


 

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