Bar Magnet

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LEVELJEE Main

A magnetic needle is kept in a non-uniform magnetic field. It experiences

(A)

a force and a torque

(B)

a force but not a torque

(C)

a torque but not a force

(D)

neither a force nor a torque

LEVELJEE Main

The magnetic field lines due to a bar magnet are correctly shown in

A magnetic compass needle oscillates 30 times per minute at a place, where the dip is $4 5^{\circ}$ and 40 times per minute, where the dip is $3 0^{\circ}$ . If $B_{1}$ and $B_{2}$ are respectively, the total magnetic field due to the earth at the two places, then the ratio $B_{1} / B_{2}$ is best given by

A magnet of total magnetic moment $1 0^{- 2} \hat{i} A-m^{2}$ is placed in a time varying magnetic field, $B \hat{i} (cos ω t)$ , where $B = 1 T$ and $ω = 0.125 rad/s$ . The work done for reversing the direction of the magnetic moment at $t = 1 s$ is

A magnetic needle of magnetic moment $6.7 \times 1 0^{- 2} Am^{2}$ and moment of inertia $7.5 \times 1 0^{- 6} kg m^{2}$ is performing simple harmonic oscillations in a magnetic field of $0.01 T$ . Time taken for 10 complete oscillations is

(A)

8.89 s

(B)

6.98 s

(C)

8.76 s

(D)

6.65 s

JEE Main 2013

LEVELJEE Advanced

Two short bar magnets of length 1 cm each have magnetic moments $1.20 Am^{2}$ and $1.00 Am^{2}$ , respectively. They are placed on a horizontal table parallel to each other with their N poles pointing towards the South. They have a common magnetic equator and are separated by a distance of 20.0 cm. The value of the resultant horizontal magnetic induction at the mid-point O of the line joining their centres is close to (Horizontal component of the earth's magnetic induction is $3.6 \times 1 0^{- 5} Wb/m^{2}$ )

(A)

3.6 \times 1 0^{- 5} Wb/m^{2}

(B)

2.56 \times 1 0^{- 4} Wb/m^{2}

(C)

3.50 \times 1 0^{- 4} Wb/m^{2}

(D)

5.80 \times 1 0^{- 4} Wb/m^{2}

JEE Main 2020

LEVELJEE Main

A small bar magnet placed with its axis at $3 0^{\circ}$ with an external field of $0.06 T$ experiences a torque of $0.018 Nm$ . The minimum work required to rotate it from its stable to unstable equilibrium position is

(A)

9.2 \times 1 0^{- 3} J

(B)

7.2 \times 1 0^{- 2} J

(C)

6.4 \times 1 0^{- 2} J

(D)

11.7 \times 1 0^{- 3} J

JEE Main 2019

LEVELJEE Main

A hoop and a solid cylinder of same mass and radius are made of a permanent magnetic material with their magnetic moment parallel to their respective axes. But the magnetic moment of hoop is twice of solid cylinder. They are placed in a uniform magnetic field in such a manner that their magnetic moments make a small angle with the field. If the oscillation periods of hoop and cylinder are $T_{h}$ and $T_{c}$ respectively, then

(A)

T_{h} = 0.5 T_{c}

(B)

T_{h} = T_{c}

(C)

T_{h} = 2 T_{c}

(D)

T_{h} = 1.5 T_{c}

JEE Main 2021

LEVELJEE Main

In a uniform magnetic field, the magnetic needle has a magnetic moment $9.85 \times 1 0^{- 2} A/m^{2}$ and moment of inertia $5 \times 1 0^{- 6} kg-m^{2}$ . If it performs 10 complete oscillations in 5 s, then the magnitude of the magnetic field is ......... mT. [Take, $π^{2}$ as 9.85]

JEE Main 2021

LEVELJEE Main

Two short magnetic dipoles $m_{1}$ and $m_{2}$ each having magnetic moment of $1 Am^{2}$ are placed at point $O$ and $P$ , respectively. The distance between $O P$ is $1 m$ . The torque experienced by the magnetic dipole $m_{2}$ due to the presence of $m_{1}$ is ...... $\times 1 0^{- 7} Nm$ .

LEVELJEE Main

A thin rectangular magnet suspended freely has a period of oscillation equal to $T$ . Now, it is broken into two equal halves (each having half of the original length) and one piece is made to oscillate freely in the same field. If its period of oscillation is $T^{'}$ , the ratio $T^{'} / T$ is

(A)

\frac{1}{2 2}

(B)

\frac{1}{2}

(C)

2

(D)

\frac{1}{4}

JEE Main 2013

LEVELBoard

The magnetic lines of force inside a bar magnet

(A)

are from North-pole to South-pole of the magnet

(B)

do not exist

(C)

depend upon the area of cross-section of the bar magnet

(D)

are from South-pole to North-pole of the magnet

JEE Main 2019

LEVELJEE Main

Two magnetic dipoles X and Y are placed at a separation d, with their axes perpendicular to each other. The dipole moment of Y is twice that of X. A particle of charge q is passing through their mid-point P, at angle $θ = 4 5^{\circ}$ with the horizontal line, as shown in figure. What would be the magnitude of force on the particle at that instant? (d is much larger than the dimensions of the dipole)

(A)

(\frac{μ _{0}}{4 π}) \frac{M}{( d /2 ) ^{3}} \times q v

(B)

(C)

2 (\frac{μ _{0}}{4 π}) \frac{M}{( d /2 ) ^{3}} \times q v

(D)

(\frac{μ _{0}}{4 π}) \frac{2 M}{( d /2 ) ^{3}} \times q v

LEVELJEE Main

A magnetic needle lying parallel to a magnetic field requires $W$ unit of work to turn it through $6 0^{\circ}$ . The torque needed to maintain the needle in this position will be

(A)

3 W

(B)

W

(C)

(3 /2) W

(D)

2 W

JEE Main 2021

LEVELJEE Main

Choose the correct option.

(A)

True dip is not mathematically related to apparent dip.

(B)

True dip is less than apparent dip.

(C)

True dip is always greater than the apparent dip.

(D)

True dip is always equal to apparent dip.

JEE Main 2019

LEVELJEE Main

At some location on earth, the horizontal component of earth's magnetic field is $18 \times 1 0^{- 6}$ T. At this location, magnetic needle of length $0.12$ m and pole strength $1.8$ A-m is suspended from its mid point using a thread, it makes $4 5^{\circ}$ angle with horizontal in equilibrium. To keep this needle horizontal, the vertical force that should be applied at one of its ends is

(A)

6.5 \times 1 0^{- 5}

(B)

3.6 \times 1 0^{- 5}

(C)

1.3 \times 1 0^{- 5}

(D)

1.8 \times 1 0^{- 5}

A magnetic needle is kept in a non-uniform magnetic field. It experiences

The magnetic field lines due to a bar magnet are correctly shown in

The magnetic lines of force inside a bar magnet

.math-text-wrapper .katex { font-size: 1.05em !important; } .math-text-wrapper .katex-display { margin: 1rem 0 !important; } A magnetic needle lying parallel to a magnetic field requires W unit of work to turn it through 60∘. The torque needed to maintain the needle in this position will be

Choose the correct option.

A magnetic needle lying parallel to a magnetic field requires $W$ unit of work to turn it through $6 0^{\circ}$ . The torque needed to maintain the needle in this position will be