CBSE Class 12 Physics Magnetic Effects Of Current And Magnetism Frequently Asked Questions

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 MAGNETIC EFFECTS OF CURRENT AND MAGNETISM

1. A circular coil of radius ‘R’ carries a current ‘I’. Write the expression for the magnetic field due to this coil at its centre. Find out the direction of the magnetic field.

2. Write the expression for the force on the charge moving in a magnetic field. Use thi expression to define the SI unit of magnetic field.

3. Define magnetic susceptibility of a material. Name two elements, one having positive susceptibility and the other having negative susceptibility. What does negative susceptibility signify?

4. Define the term magnetic dipole moment of a current loop. Write the expression for the magnetic moment when an electron revolves at a speed around an orbit of radius in hydrogen atom..

5. Explain with the help of a diagram the term ‘magnetic declination’ at a given place.

6. Define the term ‘angle of dip’. What is the value of the angle of dip at the magnetic equator? What does it mean?

7. Two wires of equal lengths are bend in the form of two loops. One of the loop is squareshaped where as the other loop is circular. These are suspended in a uniform magnetic field and the same current is passed through them. Which loop will experience greater torque? Give reasons.

8. Explain why steel is preferred for making permanent magnets while soft iron is preferred for making electromagnets.

9. Draw diagram to show behavior of magnetic field lines near a bar of 1)copper2)aluminum and3)mercury cooled at a very low temperature(4.2K)

10. How will the magnetic field intensity at the centre of the circular coil carrying current will change, if the current through the coil is doubled and radius of the coil is halved?

11. What do you mean by current sensitivity of a moving coil galvanometer? On what factors does it depend?

12. Derive an expression for the force experienced by a current carrying straight conductor placed in a magnetic field. Under what condition is this force maximum?

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13. Obtain the force per unit length experienced by two parallel conductors of infinite length carrying current in the same direction. Hence define one ampere.

14. A) If Ҳ -stands for the magnetic susceptibility of a given material, identify the class of materials for which (a) is a small positive number]. Write the range of relative magnetic permeability of these materials. B) Draw the pattern of the magnetic field lines when these materials are placed on a strong magnetic field.

15. Derive an expression for the force acting on a current carrying conductor in a magnetic field. Under what conditions this force is maximum and minimum?

16. Define the term magnetic moment of current loop. Derive the expression for the magnetic moment when an electron revolves at a speed ‘v’ around an orbit of radius

r in hydrogen atom. Also calculate the value of Bohr’s magnetic moment.

17. With the help of diagram explain how a galvanometer can be converted into an ammeter and a voltmeter.

18. To increase the current sensitivity of a moving coil galvanometer by 50%, its resistance is increased so that the new resistance becomes twice its initial resistance. By what factor does its voltage sensitivity change?

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19. Write an expression for force experienced by a charged particle moving in a uniform magnetic field? With the help of labeled diagram, explain principle and working of a cyclotron. Show that cyclotron frequency does not depend upon the speed of particles. Write its two limitations.

20. State Ampere’s Circuital Law. Derive an expression for the magnetic field at a point due to straight current carrying conductor.

21. Derive an expression for the magnetic field at a point along the axis of an air cored solenoid using a Ampere’s circuital law.

22. Derive an expression for torque acting on a rectangular current carrying loop kept in a uniform magnetic field B. Indicate the direction of torque acting on the loop.

23. With neat diagram, describe the principle, construction and working of a moving coil galvanometer. Explain the importance of radial field.

24. State Biot Savart Law. Use this law to obtain a formula for magnetic field at the centre of a circular loop of radius R ,number of turns N carrying current I. Sketch the magnetic

field lines for a current loop clearly indicating the direction of the field.

25. Distinguish the magnetic properties of dia, para- and ferro-magnetic substances interms of (i) Susceptibility, (ii) magnetic permeability and (iii) coercivity. Give one example of each of these materials.Draw the field lines due to an external magnetic field near a (i) diamagnetic,(ii) paramagnetic substance.

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