CET Moving Charges & Magnetism

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Franklin Murphy
7 years ago
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1 CET 2014 Moving Charges & Magnetism

7 1. When a charged particle moves perpendicular to the direction of uniform magnetic field its a) energy changes. b) momentum changes. c) both energy and momentum change. d) energy and momentum remain the same.

8 A Charged particle entering a magnetic field in a perpendicular direction experiences a force acting perpendicular to the path of the particle [the charged particle describes circular path in a perpendicular plane]. Therefore the magnitude of the velocity remains constant but the direction changes. Therefore, the momentum changes but the energy remains constant.

9 2. When a charged particle enters a uniform magnetic field along the direction of the field. The force experienced by the particle is a) zero. b) maximum. c) half the maximum value. d) one fourth the maximum value.

10 The magnitude of the force experienced by a charged particle moving in a magnetic field a given by F = B q v sin. When the particle moves along the direction of the field = 0 0. Sin 0 0 = 0 => F = 0

11 3. When a charged particle enters a magnetic field at angle between 0 0 and 90 0, it traces a) a helical path b) a circle c) a parabola d) a hyperbola

12 When a charged particle enters the magnetic field at right angles to it, it describes a circular path in a plane perpendicular to the magnetic field. When it enters the magnetic field at any angle between 0 0 and 90 0 it describes helical path.

17 6. Of the following graphs, the one that correctly represents the variation of magnetic field B, with the distance from he center of along straight conductor is

19 7. A circular conductor of radius R and an infinitely long straight conductor are kept as shown in figure. At the point of contact P, the two conductors are well insulated from one another. The magnetic field at the center O of the circular conductor is

20 Since the current through the coil is clockwise with respect to the observer, the magnetic Field (B 1 ), is directed in to the plane of the coil. By the right hand clasp rule, the magnetic field B 2 at O due to the infinitely long conductor is directed outwards. Therefore, the net field at O; B = B 1 -B 2

21 8. A wire loop ABCDA is formed by joining two semi circular wires of radii R 1 and R 2 as shown in figure. The magnitude of the field at their common centre O due to the current flowing through it is

22 Since the loops BC and AD carry currents in opposite direction, the magnetic field at O;

23 9. In the figure shown, the magnetic field at the center of the semi circular loop due to the current flowing through the conductor is

24 The magnetic field produced by the vertical portion is zero where as, the field produced due to semi circular loop and the horizontal portion of the wire is directed in to the plane of the paper (by right hand clasp rule.) Therefore, the resultant field B=B circle + B straight.

25 10. A rectangular loop ABCD carrying a constant current I is kept near a long straight wire carrying current as shown in figure. If a steady current I is established in the wire, then the loop will a) move towards the wire. b) move away from the wire. c) remain stationary. d) rotate parallel to the wire.

26 Since near side of the loop AB and the wire carry current in the same direction, there exists a attractive force between them. The force between the farther side CD and the wire is repulsive. But the repulsive force is less than the attractive force because AB lies close to the wire than CD. Therefore a net attractive force acts between the wire and the loop. Hence they move towards each other.

27 11. In the figure shown, the magnetic field at the centre O due to the current I is (radius of curvature R = 3 cm )

30 The magnetic field at a point on the axis of the circular coil is given by

31 14. The magnetic dipole moment of current loop is independent of a) Number of turns. b) area of loop. c) current in the loop. d) magnetic field in which it is lying. Magnetic dipole moment of current loop M = nia, it is independent of B.

34 16. A current carrying loop placed in a uniform magnetic field experiences torque. The torque experienced is independent of a) area of the loop. b) current through the loop. c) shape of the loop. d) applied magnetic field.

35 The torque experienced by the current loop nbia, where B is he strength of the applied field, I is the current and A is the area of the loop. Thus torque is independent of shape of the loop.

36 17. In a moving coil galvanometer, a radial magnetic field is used so that the galvanometer scale is a) Logarithmic. b) exponential. c) linear. d) none of these. Since the field is redial, the coil is subjected to a constant torque at all positions in the vertical plane. Therefore the scale is linear (I ).

40 19. In a cyclotron, if a deuteron can gain an energy of40 Mev,then a proton can gain an energy of a) 40 Mev b) 80 Mev c) 20 Mev d) 60 Mev

41 20. An a-particle crosses a space without any deflection. If electric E = 8 x 10 6 Vm -1 and magnetic field is B = 1.6 T, the velocity of particle is a) 2.5 x 10 6 ms -1 b) 5 x 10 6 ms -1 c) 8 x 10 6 ms -1 d) 5 x 10 7 ms -1

42 21. If a long hollow copper pipe carries a current, the magnetic field produced will be a) inside the pipe only b) outside the pipe only c) neither inside nor outside the pipe. d) both inside and outside the pipe. Current flows on the surface of the pipe, so as per Ampere s circuital law, there is no magnetic field at a point inside the pipe.

43 22. In the given figure, the loop is fixed but straight wire can move. The straight wire will a) remain stationary b) move towards the loop c) move away from the loop d) rotate about the axis.

44 Force of attraction between the wire and the left side of the loop is greater than the force of repulsion between the wire and the right side of the loop.

45 23. A circular coil carrying current is placed in a region of uniform magnetic field acting perpendicular to the plane of the coil as shown in figure. Mark the correct option. a) Coil contracts b) Coil remains the same c) Coil expands d) Coil moves

46 The coil made up of tiny current elements. Force acting on each current element is directed outwards. As a result of this the coil expands.

47 24. A wire of given length is first bent in one loop and then in three loops, If same current is passed in both cases, the ration of magnetic inductions at the center will be: a) 1 : 4 b) 1 : 9 c) 9 : 1 d) 1 : 3

49 25. If a current is passed through a spring then the spring will a) expand b) compress c) remains same d) done of these It will compress due to the force of attraction between two adjacent coils carrying current in the same direction.

50 Thank You GOOD LUCK

Magnetism. d. gives the direction of the force on a charge moving in a magnetic field. b. results in negative charges moving. clockwise.

Magnetism. d. gives the direction of the force on a charge moving in a magnetic field. b. results in negative charges moving. clockwise. Magnetism 1. An electron which moves with a speed of 3.0 10 4 m/s parallel to a uniform magnetic field of 0.40 T experiences a force of what magnitude? (e = 1.6 10 19 C) a. 4.8 10 14 N c. 2.2 10 24 N b.