A short bar-magnet placed with its axis making an angle θ with a uniform magnetic field B → experienced a torque τ → . What is the magnitude of the magnetic moment of the magnet?

Using the expression for the torque experienced by a small bar magnet when placed in uniform magnetic field, 𝜏 = m → × B → = mBsinθ Therefore, we get m = 𝜏 Bsinθ

A magnet of moment m is situated in the direction of a magnetic field B → . What is its potential energy? If it is rotated by 180 ° , then what amount of work will be done?

(i) If a bar magnet is situated along B → , ⇒ m → ∥ B → So, U = - mBcosθ = - mB Ans: U = - mB Joule (ii) If we rotate the magnet by 180 ° ,its U = - mBcos 180 ° = mB Net change in potential energy = 2 mB Ans: So, work done, W = 2 mB Joule .

E M B I B E

NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 9 - Magnetic Field and Earth's Magnetism>QUESTIONS>Q 7

EASY

12th ICSE

IMPORTANT

Earn 100

Write an expression, explaining the meanings of symbols, for the magnitude of the magnetic field due to a small bar-magnet at a point in the broad-side-on position.

Important Questions on Magnetic Field and Earth's Magnetism

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12th ICSE

IMPORTANT

NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 9 - Magnetic Field and Earth's Magnetism>QUESTIONS>Q 8

Does the magnetic axis of a freely-suspended magnet exactly point in the geographic north-south direction?

EASY

12th ICSE

IMPORTANT

NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 9 - Magnetic Field and Earth's Magnetism>QUESTIONS>Q 9

Write the relation connecting the angle of dip, horizontal and vertical components of magnetic field of earth at a place.

EASY

12th ICSE

IMPORTANT

NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 9 - Magnetic Field and Earth's Magnetism>QUESTIONS>Q 10

Do the earth's magnetic elements at a particular place vary as time passes?

EASY

12th ICSE

IMPORTANT

NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 9 - Magnetic Field and Earth's Magnetism>QUESTIONS>Q 11

Does the field of a bar-magnet exert a torque on the magnet itself?

EASY

12th ICSE

IMPORTANT

NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 9 - Magnetic Field and Earth's Magnetism>QUESTIONS>Q 12

A short bar-magnet placed with its axis making an angle

θ

with a uniform magnetic field

\vec{B}

experienced
a torque

\vec{τ}

. What is the magnitude of the magnetic moment of the magnet?

EASY

12th ICSE

IMPORTANT

NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 9 - Magnetic Field and Earth's Magnetism>QUESTIONS>Q 13

Torques

τ_{1}

and

τ_{2}

are required for a magnetic needle to remain perpendicular to the magnetic fields at two different places. What is the ratio of magnetic fields at those places?

MEDIUM

12th ICSE

IMPORTANT

NOOTAN ISC PHYSICS Class 12 Part-1>Chapter 9 - Magnetic Field and Earth's Magnetism>QUESTIONS>Q 14

A magnet of moment m is situated in the direction of a magnetic field