25 MCQs| Physics | Class XII | Magnetic Effects of Current


1.      Which of the following statements is correct with respect to charges?

a)      Moving charges produce both Electric and Magnetic field.

b)     Static charges produce both Electric and Magnetic field.

c)      Moving charges produce Electric field and not Magnetic field.

d)     Moving charges produce Magnetic field and not Electric field

 

2.      The Force on a charge q moving with a velocity v in magnetic field B, is given by :

a)      q(B x v)

b)     qBv cos θ

c)      q(v x B)

d)     None of the above

 

3.      1 Tesla is equal to :

a)      N-s/C-m

b)     N-m/C-s

c)      N-s/C

d)     C/N-m2

4.      If the magnetic field is parallel to the positive y-axis and the charged particle is moving along the positive x-axis (Fig. 4.4), which way would the Lorentz force be for (1) an electron (negative charge)


a)      -z axis

b)     +z axis

c)      Can’t be determined

d)     x-axis

5.      The radius of the circle of path formed by a charged particle (charge q, mass m) entering a magnetic field B with a velocity v is given by:

a)      qB/mv

b)     qm/Bv

c)      mB/qv

d)     mv/qB

 

6.      The velocity selector is used to:

a)      Accelerate particles until it reaches a particular velocity

b)     Particles of a specific velocity are allowed to pass through the device.

c)      It gives a selected velocity to the particles at rest.

d)     The particles are slowed down to a particular velocity which depends on Electric and Magnetic Fields.

 

7.      The following graph represents Magnetic Field versus distance r from center for a:



a)      Thin wire

b)     Thick wire of radius R

c)      Sphere of Radius R

d)     None of above

8.      A solenoid of length 0.5 m has a radius of 1 cm and is made up of 250 turns. It carries a current of 5 A. What is the magnitude of the magnetic field inside the solenoid?

a) 3.14 X 10-3 T

b) 6.28 X 10-3 T

c) 9.72 X 10-3 T

d) None of the above

 

9.      Assertion : Parallel currents attract and antiparallel currents repel even when they are not placed in any external Magnetic Field.

Reason: A current carrying loop placed in a uniform magnetic field experiences a Torque

a)      A is True, R is True and A is correct explanation of R

b)     A is True, R is True and A is not correct explanation of R

c)      A is True, R is False

d)     A is False, R is True

 

10.      Assertion: A cylindrical soft iron core is used in a moving coil galvanometer.

  Reason: It makes the field radial and strengthens the magnetic field.

a)      A is True, R is True and A is correct explanation of R

b)     A is True, R is True and A is not correct explanation of R

c)      A is True, R is False

d)     A is False, R is True

 

11.      Two thin long parallel wires separated by a distance r are carrying a current I amp. each.    The magnitude of the force per unit length applied by one wire on the other is:



12.      Two particles A and B having equal charges after being accelerated through the same potential difference enter a region of uniform magnetic field and describe circular path of radii R1 and R2 respectively. The ratio of the masses of A to B is:



13.      When a charged particle moves perpendicular to a uniform magnetic field, its:

a)      Energy and Momentum both change

b)     Energy and Momentum both don’t change

c)      Energy changes but momentum remains unchanged

d)     Momentum changes but Energy remains unchanged.

 

14.      A circular of radius R carries a current I. The magnetic field at its centre is B. At what distance from the centre on the axis of the coil, the magnetic field will be B/8?


15.      The material used for the suspension wire of a moving coil galvanometer is:

a)      Steel

b)     Constantin

c)      Phosphor-Bronze

d)     Brass

 

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

a)      Current flowing through loop

b)     Area of loop

c)      Shape of loop

d)     Magnetic Field

 

17.   A charged particle enters at 30° to the direction of magnetic field. Its path will be:

a)      Helical

b)     Hyperbolic

c)      Parabolic

d)     Straight

 

18.   Circular loop of radius 0.0157 m carries a current 2 A. The magnetic field at the centre of the loop is :

a)      1.57 × 10-3Wb/m²

b)     8.0 × 10-5 Wb/m²

c)      2.0 × 10-3 Wb/m²

d)     3.14 × 10-1 Wb/m²

 

19.   When we double the radius of a coil keeping the current through it unchanged, what happens to the magnetic field directed along its axis at far off points?

a)      Halved

b)     Doubled

c)      Quadrupled

d)     Remains unchanged

20.    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.

 

21.   A rectangular loop carrying a current i is situated near a long straight wire such that the wire is parallel to the one of the sides of the loop and is in the plane of the loop. If a steady current I is established in wire as shown in figure, the loop will



a)      rotate about an axis parallel to the wire.

b)     move away from the wire or towards right.

c)      move towards the wire.

d)     remain stationary.

 

22.   Three long, straight parallel wires, carrying current are arranged as shown in the figure. The force experienced by a 25 cm length of wire C is :



a)      10-3N

b)     2.5 X 10-3N

c)      Zero

d)     1.5 X 103 N

 

23.   The magnetic field inside a solenoid is made strong by:

a)      Putting a soft iron core inside

b)     Increasing current flowing through it.

c)      Both a) and b)

d)     None of the above

 

24.   Which of the following statements is incorrect regarding Toroidal Solenoid?

 a)      It has 0 magnetic field outside it.

 d)     The field inside a toroidal solenoid is independent of radius of solenoid, has constant magnitude and has tangential direction at every point.

 

25.   The maximum Force on a current carrying conductor of length L carrying current I placed in a magnetic field B is given by :

a)      BIL sin θ

b)     BIL cos θ

c)      BIL

d)     BIL tan θ



 Answers:

1. a)  Moving charges produce both Electric and Magnetic Field,   

2. c)  q(vXB),   

3. a)  N-s/C-m,   

4. a)  -z axis,

5. d)  mv/qB,

6. b)  Particles of a specific velocity are allowed to pass through the device,

7. b)   Thick wire of radius 'r'

8. a) 3.14 X 10-3 T

9. b)     A is True, R is True and A is not correct explanation of R

10. a)      A is True, R is True and A is correct explanation of R

11. b)

12. c)

13. d)     Momentum changes but Energy remains unchanged.

14. b)

15. c)      Phosphor-Bronze

16. c)      Shape of loop

17. a)      Helical

18. b)     8.0 × 10-5 Wb/m²

19. d)     Remains unchanged

20. d)      The electron will continue to move with uniform velocity along the axis of the solenoid.

21. c)      move towards the wire.

22. c)      Zero

23. c)      Both a) and b)

24. c)

25. c) BIL


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