MCQ Magnetism and Matter Class 12 Physics Chapter 5

MCQ Magnetism and Matter Class 12 Physics Chapter 5

 

1. What is the dimensional formula of magnetic pole strength

a)[M0L-1T0A1]

b) [M0L1T0A1]

c)[M2L1T0A2]

d) [M0L2T0A1]

 

2. A wire of length 2m is bent to form a circular coil of single turn. What is its magnetic moment in Am2 if the current in the coil is 1A

a) 2

b) 1

c) 3

d) 1/2

3. A circular coil of wire n turns has a radius r and carries a current I . Its magnetic dipole moment is M .
Now the coil is unwound and again rewound into a circular coil of half the initial radius
and the same current is passed through it, then the dipole moment of this new coil is

a)M/2

b)M/4

c)M

d)2M

4. A uniform copper wire of length L is bent into a circular coil of two turns and a current i is passed through it. The coil now behaves like a magnetic dipole of moment

a) iL2/16 π

b) iL2/8 π

c) iL2/4 π

d) iL2/2 π

5. The primary origin of magnetism lies in

a) atomic current and intrinsic spin of electrons.

b) polar and non polar nature of molecules.

c) pauli exclusion principle.

d) electronegatic nature of materials.

6. The expression for magnetic moment of revolving electron is

a) evr/2

b)(eh/4πm)n

c)(e/2m)L

d) all the above

7. The orbital speed of electron orbiting around a nucleus in a circular orbit of radius 50pm is 2.2x106m/s.Then the magnetic moment of electron is

a) 8.8×10-24Am2

b) 1.6×10-19Am2

c)8.8×10-30Am2

d)None of these

8. A closely wound solenoid of 800 turns and area of cross section 2.5×10−4m2 carries a current of 3.0A. What is its associated magnetic moment?

a)0.5Am2

b) 0.6Am

c) 0.5Am

d) 0.6Am2

9. Magnetic moment for solenoid and corresponding bar magnet is

a) equal for both

b) more for solenoid

c) more for bar magnet

d) none of these

10. The earth behaves as a magnet with magnetic field pointing approximately from the geographic

a) North to South

b) South to North

c) East to West

d) West to East

 

11. Lines of force, due to earth’s horizontal magnetic field, are

a) elliptical

b) curved lines

c) concentric circles

d) parallel and straight

12. The earth’s magnetic field at the equator is approximately 0.4 G. What is the estimated value of the earth’s dipole moment is (The radius of the earth is R=6.4 x1024 m)

a) 1.05 x1023 Am

b) 1.05 x1023 Am2

c) 2.05 x1023 Am2

d) 3.05 x1023 Am2

13. If the angles of dip at two places are 300 and 450 respectively, then the ratio of horizontal components of earth’s magnetic field at the two places will be:
a)

b)

c)

d) 1 : 2

15. Which of the following statement is not correct about the magnetic field?

a) Magnetic field lines form a continuous closed curve.

b) Magnetic field line do not interest each other.

c) Direction of tangent at any point on the magnetic field line curve gives the direction of magnetic field at that point.

d) Outside the magnet, magnetic field lines go from South to North pole of the magnet.

16.The magnetic field lines inside a bar magnet:

a) do not exist

b) depends on area of cross-section of bar magnet

c) are from N-pole to S-pole of the magnet

d) are from S-pole to N-pole of the magnet.

17. The Direction of net magnetic field at any point in the magnetic field is————————–

a) Always South to North at all points of the field

b) Always North to South at all points of the field

c) Tangential to the field line at that point

d) Normal to the field line at that point

18. What is the strength of magnetic field known as ________

a) Magnetic flux

b) Density
c) Intensity of magnetisation

d) Magnetic flux density

19.The net magnetic flux through any closed surface, kept in a magnetic field is

a) zero

b) μ0/4π

c) 4π/μ0

d) 4μ0/π

20.At a place the angle of dip is 30°. If the horizontal component of earth’s magnetic field is HE, then the total field intensity will be given by

a) HE /2

b) 2 HE /√3

c) HE / √2

d) HE /√3

21.The Earth always have both horizontal and vertical components everywhere.

a)True

b)False

22.When is the angle of dip at a place equal to 45o?

a) When the vertical and horizontal components of earth’s magnetic field are equal

b) When the vertical component is twice the horizontal component of earth’s magnetic field

c) When the vertical component is half the horizontal component of earth’s magnetic field

d) When either the vertical component or the horizontal components of earth’s magnetic field is equal to zero

 

23.The magnetic field of Earth can be modelled by that of a point dipole placed at the centre of the Earth. The dipole axis makes an angle of 11.3° with the axis of Earth. At Mumbai, ‘declination is nearly zero. Then,

a) the declination varies between 11.3° W to 11.3° E.

b) the least declination is 0°

c) the plane defined by dipole axis and Earth axis passes through Greenwich.

d) declination averaged over Earth must be always negative.

 

24.Which of the following is responsible for the earth’s magnetic field?

а) Convective currents in earth’s core

b) Diversive current in earth’s core.

c) Rotational motion of earth.

d) Translational motion of earth.

 

25 How many quantities are required to specify the magnetic field of the earth?

a) 1

b) 2

c) 3

d) 4

 

26. Which of the following is the definition for magnetic meridian of Earth?

a) Vertical plane passing through the axis of a freely suspended or pivoted magnet

b) Horizontal plane passing through the axis of a freely suspended or pivoted magnet

c) Vertical plane passing through the geographical North Pole and South Pole at a given place

d) Horizontal plane passing through the geographical North Pole and South Pole at a given place

 

27. Which among the following is denoted by δ?

a) Horizontal component

b) Magnetic meridian

c) Magnetic declination

d) Magnetic inclination

 

28. A long magnet is cut into two parts such that the ratio of their lengths is 2:1. What is the ratio pole strength of both the section?

a) 1:2

b) 2:1

c) 4:1

d) Equal

 

29.Which of the following statements is true about magnetic field intensity?

a) Magnetic field intensity is the number of lines of force crossing per unit volume.

b) Magnetic field intensity is the number of lines of force crossing per unit area.

c) Magnetic field intensity is the magnetic induction force acting on a unit magnetic pole.

d) Magnetic field intensity is the magnetic moment per unit volume.

 

30. What happens to the magnetic moment if a hole is made at the centre of a bar magnet?

a) Decreases

b) Increases

c) Does Not change

d) None of the above

 

Assertion and Reasoning type of questions

 

Directions for assertion & reason questions

These questions consist of two statements each , printed as assertion and reason. while answering these questions you have to choose any one of the following four responses.
(A) if both assertion& reason are true &the reason is a correct explanation of the assertion.
(B) if both assertion& reason are true but the reason is not a correct explanation of the assertion.
(C) if assertion is true but the reason is false.
(D) if assertion is false but reason is true

31 . Assertion : When radius of a circular loop carrying current is doubled, its magnetic moment becomes four times.
Reason : Magnetic moment depends on area of the loop.

 

32. Assertion :The magnetic moment (μ) of an electron revolving around the nucleus decreases with increasing principle quantum number (n).
Reason :Magnetic moment of the revolving electron μ n

 

33. Assertion : The magnetic field produced by a current carrying solenoid is independent of its length and cross-sectional area.
Reason : The magnetic field inside the solenoid is uniform.

 

34. Assertion :The ends of a magnet suspended freely point out always along north south direction.
Reason : Earth behaves as a huge magnet.

 

35. Assertion :The angle of dip is maximum at the poles of the earth.
Reason :The magnetic field lines are parallel to the surface of the earth at the poles.

 

 

 

 

 

 

 

 

KEY FOR THE QUESTIONS
1. b 2.c 3.a 4.b 5.a
6.d 7.a 8.d 9.a 10.d
11.b 12.d 13.b 14.a 15.d

16.d 17. c 18.d 19.a 20.b
21.b 22.a 23.a 24.a 25.c
26.a 27.d 28.d 29.c 30.c
31.b 32.d 33.b 34.a 35.c
Hints:
2. Length of the wire =2m, when bent becomes circumference (c) of the loop, whose radius is given by
:
r=c/2 π=(2/2 π)=(1/ π)
Thus, area of loop :-
A=πr2=π(1/π)2=1/π m2
So, the magnetic moment of the loop in,
M=IA=(1/π)Am2.
3.
40
4.
7.
41
8.
Given: n=800,
A=2.5×10−4m2,
I=3.0A
A magnetic field develops along the axis of the solenoid. Therefore current-carrying solenoid acts like a
bar magnet.
m=nIA=800×3×2.5×10−4
=0.6Am2 along the axis of the solenoid.
13.Bequatorial=μ0/4π×M/d3⇒
Here μ0 is the permeability of free space, M is the dipole moment of the magnet, d is the
distance of the point from the equator of the magnet, and
Bequatorials the magnetic field of the magnetic field at the equator of the magnet.
for any point on the equator d=R=6400Km=6400×103m
Also, the value of the magnetic field is given as
⇒B=0.4G=0.4×10-4,T
On calculation
Earth’s dipole moment at the equator will be 1.05×1023Am

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