Magnetism and Matter Test 28

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Magnetism and Matter Test 28

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Question 1
1 / -0

The torque and magnetic potential energy of a magnetic dipole in most stable position in a uniform magnetic field($$\bar{B}$$) having magnetic moment ($$\bar{m}$$) will be.

A
$$-$$mB, zero

B
mB, zero

C
Zero, mB

D
Zero, $$-$$mB

Solution

Torque, $$\bar{\tau}=\vec{m}\times \vec{B}=mB\sin\theta$$
and magnetic potential energy $$U_m=\vec{m}\cdot \vec{B}=mB\cos \theta$$
at $$\theta =0^o$$ the dipole will be in most stable position
$$\tau =mB\sin\theta =mB\sin 0^o=0$$
and $$U_m=-mB\cos\theta =-mB\cos \theta^o=-mB$$
Question 2
1 / -0

If a magnetic material is having magnetic susceptibility $$(\chi)=-1$$, then the relative magnetic permeability $$(\mu_r)$$ and type of magnetic material is?

A
$$0$$, diamagnetic

B
$$2$$, ferromagnetic

C
$$1$$, paramagnetic

D
$$-1$$, diamagnetic

Solution

Here, $$\chi =-1$$
then $$\mu_r=1+\chi \Rightarrow \mu_r=1+(-1)=I-1=0$$
Since, magnetic susceptibility of given material is less than one. Hence, the given magnetic material is a diamagnetic material.
Question 3
1 / -0

Assertion : Substances which at room temperature retain their ferromagnetic property for a long period of time are called permanent magnets.
Reason : Permanent magnet can be made by placing a ferromagnetic rod in a solenoid and passing current through it.

A
If both assertion and reason are true and reason is the correct explanation of assertion.

B
If both assertion and reason are true and reason is not the correct explanation of assertion.

C
If assertion is true but reason is false.

D
If both assertion and reason are false.

Solution

To make a permanent magnet, place a ferromagnetic rod in a solenoid and pass a current through it. The magnetic field of the solenoid magnetises the rod.
Question 4
1 / -0

Assertion : At high temperature, a ferromagnet becomes a paramagnet.
Reason : The ferromagnetic property depends on temperature.

A
If both assertion and reason are true and reason is the correct explanation of assertion.

B
If both assertion and reason are true and reason is not the correct explanation of assertion.

C
If assertion is true but reason is false.

D
If both assertion and reason are false.

Solution

At enough high temperature, a ferromagnet become a paramagnet. The domain structure disintegrates with temperature.
Question 5
1 / -0

A ball of superconducting material is dipped in liquid nitrogen and placed near a bar magnet. In which direction will it move?

A
Away from bar magnet

B
Towards the bar magnet

C
Around the bar magnet

D
Remain constant

Solution

Since, superconducting material and liquid nitrogen both are diamagnetic in nature, the dipped ball of superconductor in liquid nitrogen also behaves as a diamagnetic material. When it is placed near a bar magnet it will be repelled.
Question 6
1 / -0

Two magnets of movement M and 2M are tied at an angle of $$60^0$$ to each other. What is the resultant magnetic moment of the combination?

A
$$\sqrt7M$$

B
$$\sqrt8M$$

C
$$\sqrt9M$$

D
$$\sqrt10M$$

Solution
Question 7
1 / -0

Short Answer Type Question.
Which magnetic property is present in all substances?

A
Diamagnetism

B
massless

C
frictionless

D
no common property

Solution
Question 8
1 / -0

The magnetic field of earth at the equator is approximately $$4\times 10^{-5}\ T$$. The radius of earth is $$6.4\times 10^{6}\ m$$. Then the dipole moment of the earth will be near the order of

A
$$10^{23}\ A\ m^{2}$$

B
$$10^{20}\ A\ m^{2}$$

C
$$10^{16}\ A\ m^{2}$$

D
$$10^{10}\ A\ m^{2}$$

Solution

$$B=\cfrac {\mu_om}{4 \pi d^3}= \cfrac {4 \times 10^{-7}}{4 \pi (6.4 \times 10^6)^3}= \approx 10^{23} Am^2$$
Question 9
1 / -0

The coercivity of a small magnet where the ferromagnet gets demagnetized is $$3\times 10^{3}\ Am^{-1}$$. The current required to be passed in a solenoid of length $$10\ cm$$ and number of turns $$100$$, so that the magnet gets demagnetized when inside the solenoid, is:

A
$$3A$$

B
$$6A$$

C
$$30\ mA$$

D
$$60\ mA$$

Solution

Coercivity refers to the intensity of magnetic fields $$(B)$$ where the magnet gets demagnetised
For solenoid we have, $$B=\mu _{0}nI$$
($$\mu _{0}=$$ absolute permeability, $$n= $$ no. of turns per unit length, $$B=$$ Magnetic field in solenoid , I= current through each turn)
$$\Rightarrow \mu _{0}H= \mu _{0}nI$$ ($$H=$$ intensity of magnetic field)
$$\Rightarrow I=\dfrac{H}{n}$$
$$\Rightarrow I=\dfrac{3\times 10^{3}A/m}{\dfrac{100}{0.1 m}}=3A$$
So current needed to be passed through solenoid $$=3A$$
Question 10
1 / -0

Core of electromagnets are made of ferromagnetic materials which have.

A
Low permeability and low retentivity

B
High permeability and high retentivity

C
High permeability and low retentivity

D
Low permeability and high retentivity
Solution
Electromagnetic cores should have:
High permeability so that it supports the formation of a magnetic field within itself.
Low retentivity so that the magetic field so that it gets demagnetized easily.
And Ferromagnetic materials are used to make electromagnets cores
Because:-
Ferromagnetic materials have high permeability and low retentivity.

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Magnetism and Matter Test 28

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Question 1

$$-$$mB, zero

mB, zero

Zero, mB

Zero, $$-$$mB

Solution

Question 2

$$0$$, diamagnetic

$$2$$, ferromagnetic

$$1$$, paramagnetic

$$-1$$, diamagnetic

Solution

Question 3

If both assertion and reason are true and reason is the correct explanation of assertion.

If both assertion and reason are true and reason is not the correct explanation of assertion.

If assertion is true but reason is false.

If both assertion and reason are false.

Solution

Question 4

If both assertion and reason are true and reason is the correct explanation of assertion.

If both assertion and reason are true and reason is not the correct explanation of assertion.

If assertion is true but reason is false.

If both assertion and reason are false.

Solution

Question 5

Away from bar magnet

Towards the bar magnet

Around the bar magnet

Remain constant

Solution

Question 6

$$\sqrt7M$$

$$\sqrt8M$$

$$\sqrt9M$$

$$\sqrt10M$$

Solution

Question 7

Diamagnetism

massless

frictionless

no common property

Solution

Question 8

$$10^{23}\ A\ m^{2}$$

$$10^{20}\ A\ m^{2}$$

$$10^{16}\ A\ m^{2}$$

$$10^{10}\ A\ m^{2}$$

Solution

Question 9

$$3A$$

$$6A$$

$$30\ mA$$

$$60\ mA$$

Solution

Question 10

Low permeability and low retentivity

High permeability and high retentivity

High permeability and low retentivity

Low permeability and high retentivity

Solution

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