CLASS 12 PHYSICS - ASSIGNMENT 5 - MAGNETISM

 CLASS 12 

PHYSICS

MAGNETISM


1. Define magnet and magnetism.


2. What are artificial magnets?  Name their common shapes.


3. Define 1. Magnetic field

                2. Uniform magnetic field

                3. Magnetic poles

                4. Magnetic axis


4. State the properties of magnets.


5. State Coulomb's law of magnetic force.  


6. Define unit magnetic pole.


7. What is the source of magnetic field or magnetism?


8. Repulsion is the surer test of magnetism.  Comment.


9. What is the origin of the word magnetism?


10.  Define 1. Magnetic equator

                   2. Magnetic length

                   3. Magnetic dipole

                   4. Magnetic dipole moment


11. What are magnetic lines of force. Give their important properties.


12. Describe a method for plotting magnetic field of a bar magnet.


13. Write the formula for the magnetic field intensity at a point on the axis of a bar magnet.  What is the direction of the field?


14.  Write the formula for the magnetic field intensity at a point on the equatorial line of a bar magnet.  What is the direction of this field?


15. What is the magnitude of the equatorial and axial fields due to a bar magnet of length 5 cm at a distance of 50 cm from the midpoint? The magnetic moment of the bar magnet is 0.40 Am².


16.  Can two magnetic lines of force intersect.  Justify your answer.


17.  Magnetic lines of force always form closed loops.  Comment.


18. How are magnetic field lines different from the electrostatic field lines?


19.  What is a natural magnet?


20.  The earth's magnetic field varies from point to point in space. Does it also change with time?  If so, on what time scale does it change appreciably?


21.  A short bar magnet placed with its axis at 30° with a uniform external magnetic field of 0.25 T experiences a torque of magnitude equal to 4.5 x 10⁻²   J.  What is the magnetic moment of the magnet?


22. A closely wound solenoid of 800 turns and area of cross-section 2.5 x 10⁻⁴ m² carries a current of 3.0 A.  Explain in what sense does the solenoid act like a bar magnet.  What is its associated magnetic moment?


23. Derive an expression for the torque on a magnetic dipole placed in a uniform magnetic field.  Hence define magnetic dipole moment.


24.  Write the SI unit of:

1. Magnetic field

2. Pole strength

3. Magnetic dipole moment

4. Force


25. On which factors does the pole strength of a magnet depend?


26.  In a uniform magnetic field, when is the torque on a magnet (i) maximum and (ii) minimum?


27.  Are the two poles of a magnet equally strong?


28.  What does the word lodestone mean?


29.  What is magnetic axis of the earth?


30.  What is the order of magnitude of earth's magnetic field near its surface.


31.  Is magnetic moment a vector? If yes, give its direction.


32. Who first discovered earth's magnetism.


33. Why does a bar magnet always stand in north-south direction, when freely suspended?


34.  Why is a current loop considered a magnetic dipole?


35.  State Gauss's law of magnetism.  What does it indicate?


36. Define Bohr magnetron and write its value.


37. Describe some of the properties of paramagnetic, diamagnetic and ferromagnetic substances.

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