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Worksheet on Magnetism and matter

Q1 A toroid of n turns, mean radius R and cross-sectional radius a carries current I. It is placed on a horizontal table taken as x-y plane. Its magnetic moment m.


a) is non-zero and points in the z-direction by symmetry.

b) points along the axis of the toroid (m = mɸ).

c) is zero, otherwise there would be a field falling as 1/r to the power (3) at large distances outside the toroid.

d) is pointing radially outwards.




Q2 In a permanent magnet at room temperature.


a) magnetic moment of each molecule is zero.

b) the individual molecules have non-zero magnetic moment which are all perfectly aligned.

c) domains are partially aligned.

d) domains are all perfectly aligned..



Q3 S is the surface of a lump of magnetic material.


a) Lines of B are not necessarily continuous across S.

b) Some lines of B must be discontinuous across S.

c) Lines of H are necessarily continuous across S.

d) Lines of H cannot all be continuous across S.



Q4 A magnetic needle is kept in a non-uniform magnetic field. It experiences.


a) a torque but not a force.

b) neither a force nor a torque.

c) a force and a torque.

d) a force but not a torque.



Q5 The material suitable for making electromagnets should have.


a) high retentivity and high coercivity.

b) low retentivity and low coercivity.

c) high retentivity and low coercivity.

d) low retentivity and high coercivity.



Q6 Which of the following materials is repelled by an external magnetic field :-


a) Iron

b) Cobalt

c) Steel

d) Copper



Q7 Assertion :- A planar circular loop of area A and current 'I' is equivalent to magnetic dipole of dipole moment M = 'IA'.

Reason :- At large distances, magnetic field of circular loop and magnetic dipole is same.


a) A

b) B

c) C

d) D



Q8 Assertion :- Magnetic force between two charges is generally much smaller than the electric force between them.

Reason :- Speeds of charges are much smaller than the free-space speed of light.


a) A

b) B

c) C

d) D



Q9 Assertion :- A moving charged particle gets energy from magnetic field.

Reason :- Magnetic force works on moving charged particle.


a) A

b) B

c) C

d) D



Q10 Assertion :- Magnetic field of an atom is due to both, the orbital motion and spin motion of electron.

Reason :- A moving charge particle produces magnetic field.


a) A

b) B

c) C

d) D



Q11 Assertion :- Soft iron is used as transformer core.

Reason :- Soft iron has narrow hysteresis loop.


a) A

b) B

c) C

d) D



Q12 Assertion :- We cannot think of a magnetic field configuration with three poles.

Reason :- A bar magnet does exerts a torque on itself due to its own field.


a) A

b) B

c) C

d) D



Q13 Assertion :- The true geographic north direction is found by using a compass needle.

Reason :-The magnetic meridian of the earth is along the axis of rotation of the earth.


a) A

b) B

c) C

d) D



Q14 Assertion :- Magnetic poles are only mathematical assumptions having no real existence.

Reason :- A charged particle is moved along a magnetic field line. The magnetic force on the particle is perpendicular to its velocity.


a) A

b) B

c) C

d) D



Q15 Assertion :- A compass needle which is allowed to move in a horizontal plane is taken to a geomagnetic pole. It will stay in any direction.

Reason :- At geomagnetic pole BH = 0


a) A

b) B

c) C

d) D



Q16 Assertion :- Work done by magnetic field on a moving charge is zero.

Reason :- Force experienced by a moving charge in a magnetic field is may be zero.


a) A

b) B

c) C

d) D



Q17 Gauss’s law in magnetism indicates that magnetic ____________ do not exist.



Q18 Magnetic dipole moment associated with an electron due to its orbital motion in first orbit of H-atom is known as__________



Q19 Magnetic lines of force form closed loop. They converge at__________ pole and diverge at__________ pole.



Q20 Angle between the geographical meridian and magnetic meridian at the given place is known as__________



Q21 Angle made by the earth’s total magnetic field with the horizontal direction is known as_________



Q22 Magnetic moment developed per unit volume of a material when placed in a magnetizing field is known as_________



Q23 A magnetic dipole is placed in a uniform magnetic field. The net magnetic force on the dipole is________.



Q24 The magnetic moment of a magnet of length 10 cm and pole strength 4.0 Am will be_________ .



Q25 A magnet of magnetic moment M is situated with its axis along the direction of a magnetic field of strength B. The work done in rotating it by an angle of 180 degree will be________





ANSWERS


1) c

2) c

3) d

4) c

5) c

6) d

7) a

8) a

9) d

10) a

11) a

12) d

13) d

14) c

15) a

16) b

17) monopoles

18) Bohr magneton

19) south, north

20) magnetic declination

21) angle of dip

22) intensity of magnetisation

23) zero

24) 0.4

25) 2MB



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