NCERT Class 12 Chapter 4 Physics Moving Charges and Magnetism MCQ

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1. Biot-Savart law indicates that the moving electrons (velocity v) produce a magnetic field B such that

A. B is perpendicular of

B. B is parallel to v

C. it obeys inverse cube law

D. it is along the line joining the electron and point of observationt

2. A charged particle is moving in a cyclotron, what effect on the radius of path of this charged particle will occur when the frequency of the ratio frequency field is doubled?

A. It will also be doubled.

B. It will be halved

C. It will be increased by four times.

D. It will remain unchanged.

3. According to Gauss’s theorem in magnetism, surface integral of magnetic field intensity over a surface (closed or open) is always:

A. -1

B. 1

C. 0

D. infinity

4. A current carrying circular loop of radius R is placed in the x-y plane with centre at the origin. Half of the loop with x > 0 is now bent so that it now lies in the y-z plane.

A. The magnitude of magnetic moment now diminishes

B. The magnetic moment does not change

C. The magnitude of B at (0, 0, z), z > R increases

D. The magnitude of B at (0, 0, z), z >> R is unchanged

5. Which of the following is not correct about cyclotron?

A. It is a machine to accelerate charged particles or ions to high energies.

B. Cyclotron uses both electric and magnetic fields in combination to increase the energy of charged particles.

C. The operation of the cyclotron is based on the fact that the time for one revolution of an ion is independent of its speed or radius of its orbit.

D. The charged particles and ions in cyclotron can move on any arbitrary path.

6. Tesla is a unit of:

A. electric flux

B. magnetic flux

C. magnetic field

D. electric field

7. An electron is projected with uniform velocity along the axis of a current carrying long solenoid. Which of the following is true?

A. The electron will be accelerated along the axis

B. The electron path will be circular about the axis

C. The electron will experience a force at 45° to the axis and hence execute a helical path

D. The electron will continue to move with uniform velocity along the axis of the solenoid

8. The nature of parallel and anti-parallel currents are

A. parallel currents repel and antiparallel cur¬rents attract.

B. parallel currents attract and antiparallel cur-rents repel

C. both currents attract.

D. both currents repel

9. In a cyclotron, a charged particle

A. undergoes acceleration all the time

B. speeds up between the dees because of the magnetic field

C. speeds up in a dees

D. slows down within a dee and speeds up between dees

10. Current flows through uniform, square frames as shown in the figure. In which case is the magnetic field at the centre of the frame not zero? CBSE Class12 Moving Charges and Magnetism (10Q)

CBSE Class12 Moving Charges and Magnetism (10Q)

A. (a)

B. (b)

C. (c)

D. (d)

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11. The magnetic moment of a current I carrying circular coil of radius r and number of turns N varies as

A. 1r²

B. 1r

C. 1

D. r²

12. If we double the radius of a coil keeping the current through it unchanged, then the magnetic field at any point at a large distance from the centre becomes approximately

A. double

B. three times

C. four times

D. one-fourth

13. Ampere’s circuital law is given by CBSE Class12 Moving Charges and Magnetism (13Q)

A. (a)

B. (b)

C. (c)

D. (d)

14. A short bar magnet has a magnetic moment of 0. 65 J T-1, then the magnitude and direction of the magnetic field produced by the magnet at a distance 8 cm from the centre of magnet on the axis is

A. 2.5 × 10-4 T, along NS direction

B. 2.5 × 10-4 T along SN direction

C. 4.5 × 10-4 T, along NS direction

D. 4.5 × 10-4 T, along SN direction

15. A proton and an alpha particle both enter a region of uniform magnetic field B, moving at right angles to field B. If the radius of circular orbits for both the particles is equal and the kinetic energy acquired by proton is 1 MeV the energy acquired by the alpha particle will be:

A. 0.5 MeV

B. 1.5 MeV

C. 1 MeV

D. 4 MeV

16. Two identical current carrying coaxial loops, carry current I in opposite sense. A simple amperian loop passes through both of them once. Calling the loop as C, then which statement is correct? CBSE Class12 Moving Charges and Magnetism (16Q)

CBSE Class12 Moving Charges and Magnetism (16Q)

A. (a)

B. (b)

C. (c)

D. (d)

17. A current carrying loop is placed in a uniform magnetic field. The torqe acting on it does not depend upon

A. area of loop

B. value of current

C. magnetic field

D. None of these

18. A charged particle moving in a uniform magnetic field and losses 4% of its kinetic energy. The radius of curvature of its path changes by

A. 2%

B. 4%

C. 10%

D. 12%

19. The correct plot of the magnitude of magnetic field B⃗ vs distance r from centre of the wire is, if the radius of wire is R CBSE Class12 Moving Charges and Magnetism (19Q)

CBSE Class12 Moving Charges and Magnetism (19Q)

A. (a)

B. (b)

C. (c)

D. (d)

20. The sensitivity of a tangent galvanometer can be increased by increasing:

A. the radius of the coil

B. the external magnetic field

C. the number of turns of the coil

D. all the above

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21. Two particles X and Y having equal charges, after being accelerated through the same potential difference, enter a region of uniform magnetic field and describe circular paths of radii R1 and R2, respectively. The ratio of masses of X

A. (R₁/R₂)^1/2

B. (R₂/R₁)

C. (R₁/R₂)₂

D. (R₁/R₂)

22. The nature of parallel and anti-parallel currents are

A. parallel currents repel and antiparallel cur¬rents attract.

B. parallel currents attract and antiparallel cur-rents repel

C. both currents attract.

D. both currents repel

23. The permeability of a paramagnetic substance is:

A. very large

B. small but more than unity

C. less than unity

D. negative

24. Choose the correct option
Assertion : Free electrons always keep on moving in a conductor even then no magnetic force act on them in magnetic field unless a current is passed through it.
Reason : The average velocity of free electron is zero.

A. Assertion is correct, reason is correct; reason is a correct explanation for assertion.

B. Assertion is correct, reason is correct; reason is not a correct explanation for assertion

C. Assertion is correct, reason is incorrect

D. Assertion is incorrect, reason is correct

25. Which of the following shows that the earth behaves as a magnet?

A. Repulsion between like poles

B. Attraction between unlike poles

C. Null points in the magnetic field of a bar magnet

D. No existence of isolated magnetic poles