Magnetic Effects of Current Magnetism

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1. Suppose a helical spring is suspended from the roof of a room and very small weight is attached to its lower end what will happen to the spring when a current is passed through it?Give reason to support your answer?

2. One alpha particle and a deuteron entered perpendicularly in a uniform magnetic field with
same velocity. Which one follow the greater circle?

3. Out of Voltmeter and Millivoltmeter, which has the higher resistance?

4. Proton is moving along the axis of a solenoid carrying current of 2 A and 50 number of turns per unit length. What will be the force acting on the particle.

5. Out of Ammeter and Milliammeter, which has the higher resistance?

6. What will be the direction of magnetic field at point O

7. Can a Moving Coil Galvanometer can be used to detect an A.C. in a circuit .Give reason.

8. Two wires of equal length are bent in the form of two loops. One loop is square whereas the other is circular. These are suspended in same magnetic field and same current is passed through them. Explain with reason which will experience greater torque?

9. The pole of a magnet is brought near to a stationary charge. What will be the force experienced by pole?

10. A charge particle moving in a magnetic field penetrates a layer of lead and thereby losses half of its kinetic energy. How does the radius of curvature of its path change?

11. A Voltmeter, an ammeter and a resistance are connected in series with a battery. There is some deflection in voltmeter but the deflection of ammeter is zero. Explain why?

12. A Current ‘I’ flows along the length of an infinitely long straight thin walled pipe. What is the magnetic field at any point on the axis of pipe?

13. The Earth’s core contains iron but geologists do not regard this as a source of Magnetic Field, Why?

14.Is the Resistance of Voltmeter larger than or smaller than the resistance of Galvanometer from which it is converted.

15. A Magnetic Field dipole placed in a Magnetic Field experiences a net force. What can you say about the Nature of Magnetic Field?

16. Earth’s Magnetic Field does not affect working of moving Coil Galvanometer. Why?

17. Which type of Magnetism exists in all substances?

18.For what orientation P.E. of a Magnetic dipole placed in uniform Magnetic Field minimum?

19. How does a ferromagnetic material change its Magnetic properties if it is heated beyond its curie temperature?

20.A bar magnet is cut into two pieces, along its length. How will its pole strength be affected?

21.What is the work done by a magnetic force, in displacing a charged particle?

22. What is the net magnetic flux from a north (or south) pole of a magnet (dipole) ?

23.An unmagnetised ferromagnetic substance is magnetized. Given figure shows the B-H curve. Identify the stage of saturation ,reverse region and irreversible region

stage of saturation is B to C . Reversible region O to A and A to B is irreversible region.

24. What is the magneticfield at the centre of the following circular coils carrying current I?

25. Two long straight wires are set parallel to each other. Each carries a current I in the same direction and the separation between them is 2r. What is the intensity of the magnetic field midway between them?

26.A proton is about 1840 times heavier than an electron. What will be its kinetic energy when it is accelerated by a potential difference of 1KV?

27. . A circular loop of radius R carrying current I ,lies in X-Y plane with its centre at origin.What is the total magnetic flux through X-Y plane?

28.. A hypothetical bar magnet is cut into two equal pieces and placed as shown in the figure. What is the magnetic moment of this arrangement?

29. A circular current carrying coil has a radius R. What is the distance from the centre of the coil on its axis where the magnetic field is 1/8 th of its value at the centre?

30. A magnetic needle suspended freely in a uniform magnetic field experiences torque but no net force. A nail made up of iron kept near a bar magnet experience a force of attraction and torque .Give reason.

31.What is the work done by a magnetic field on moving a charge? Give reason.

32. A particle with charge q moving with velocity v in the plane of the paper enters a uniform magnetic field B acting perpendicular to the plane of the paper. Deduce an expression for the time period of the charge as it moves in a circular path in the field . Why does the kinetic energy of the charge not change while moving in the magnetic field.

33. A solenoid of length 0.6m has a radius of 1cm and is made up of 600 turns.It carries a current of 5A.What is the magnetic field inside and at ends of solenoid.?

34. An element dl = dx i is placed at the origin and carries a large current I = 10A.What is the magnetic field on the y axis at a distance of 0.5m,

35. You are given a copper wire carrying current I of length L. Now the wire is turned into circular coil. Find the number of turns in the coil so that the torque at the centre of the coil is to maximum.

36. What is the magnetic field produced at the centre of curvature of an arc of wire of radius r carrying current I subtends an angle P /2radians at its centre.

37. If B is the magnetic field produced at the centre of a circular coil of one turn of length L carrying current I then what is the magnetic field at the centre of the same coil which is made into 10 turns?

38. A copper wire is bent into a square of each side 6cm.If a current of 2A is passed through a wire what is the magnetic field at the centre of the square?

39. Find the magnetic moment of a wire of length l carrying current I bent in the form of a circle.

40. When current is flowing through two parallel conductors in the same direction they attract while two beams of electrons moving in the same direction repel each other. Why?

41. Draw diagrams to show behavior of magnetic field lines near a bar of (i) Alluminium (ii) copper and (iii) mercury cooled to a very low temperature 4.2 K

42. The hysteresis loss for a sample of 6 kg is 150 J/M2/cycle. If the density of iron is 7500 kg/m3, calculate the energy loss per hour at 40cycle.

43. A current carrying solenoid of 100 turns has an area of cross section 10-4 m2 .When suspended freely through its centre, it can turn in a horizontal plane .what is the magnetic moment of the solenoid for a current of 5A.Also calculate the net force and torque on solenoid if a uniform horizontal field of 10x10-2 T is set up at an angle of 30 degree with axis of solenoid when it is carrying the same current.

44. Two concentric circular coils A and B of radii 10 cm and 6 cm respectively, lie in the same vertical plane containing the north to south direction. coil A has 30 turns and carries a current of 10 A . Coil B has 40 turns and carries a current of 15 A .the sense of the current in A is anticlockwise and clockwise in B for an observer looking at the coils facing west. Give the magnitude and direction of net magnetic field

45. The vertical component of earth’s magnetic field at a given place is 3 times its horizontal component. If the total intensity of earth’s magnetic field at a place is 0.4 G , find the value of horizontal component of earths field and angle of dip.

46. north to south direction.Specify the direction in which the uniform magnetic field should be set up to prevent the electron from deflecting from its straight line path.

47. A straight horizontal conducting rod of length 0.5 m and mass 50 g is suspended by two vertical wires at its ends.A current of 5A is set up in the rod sdthrough the wires.(i) What magbnetric field should be set up normal to the conductor in order that the tension in the wires is zero?(ii)What will be the tension in the wire if the direction of current is reversed keeping the magbetic field same as before?(neglect the mass if wure abd taje g=10m/s2 )

48. A circular coil of 20 turns and radius 10cm is placed in a uniform magnetic field of 0.d10T normal to the plane of the coil.If the current in the coil is 5a,What is the (i)Total torque on the coil (ii) total force on the coil (iii) average dsforce on each electron in the coil due to the magnetic field.(coil is made of copper, A= 10-5 m2 ,free electron density in copper is 1029 /m3)

49. A Rowland ring of mean radius 15 cm has 3500 turns of wore wound on a ferromagnetic core of relative permeability 800.What is the magnetic field B in the core for a magnetizing current of 1.2 A?

50. A straight wire of mass 200g and the length 1.5m carries a current of 2A. It is suspended in mid air by a uniform horizontal magnetic field B. What is the magnitude of B in tesla?

51. A rigid circular loop of radius r and mass m lies in the x-y plane of a flat table and has a current I flowing in it. At this particular place the earth’s magnetic field is B = Bxi +Bzk. What is the value of I, so that loop starts tilting?

52. In an ammeter, 10% of main current is passing through the galvanometer. If the resistance of the galvanometer is G, then what is the shunt resistance in ohms?

53. The two rails of arailway track insulated from each other and the ground is connected to a milli voltmeter. What is the reading g of the millivolmeter when the train passes at aspeed 180km/hr along the track, given that the vertical component of earth”s magnetic field is 0.2x10-4T and rails are separated by 1m
e = Blv = 0.2x10-4x1x180x5/18
= 10-3V = 1Mv

54. A charged particle moving in a magnetic field penetrates a layer of lead and there by looses half of its kinetic energy.How does the radius of curvature of its path changes? Radius r= mV/qB

54. The velocities of two α particles X and Y entering in an uniform magnetic field are in the ratio 2:1.On entering the field ,they move in different circular paths .Give the ratio of the radii of their paths?

55. In an exercise to increase current sensitivity of a galvanometer by 25 % , its resisitance is increased by 1.5 times . How does the voltage sensititvity of the galvanometer be affected.


CBSE Physics (Chapter Wise With Hint / Solution) Class XII (By Mr. Sreekumaran Nair)