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Previous Year Selected Questions From Magnetic Effect Of electric Current

  1. (a) State Fleming’s left hand rule.   (2018)
    (b) Write the principle of working of an electric motor.
    (c) Explain the function of following parts of an electric motor:
    (i) Armature (ii) Brushes (iii) Split ring.
  2.  (a) How is the strength of the magnetic field at a  point near a straight conductor related to the strength of the electric current flowing in the conductor ?  2016
    (b) With the help of a diagram describe an activity to show that a straight conductor carrying current produces a magnetic field around it. State the rule which may be used to determine the direction of magnetic field thus produced.
    (c) Why do two magnetic field lines never intersect each other ? Explain. [5]
    Answer :
    (a) The magnetic field produced around a straight current carrying conductor increases
    on increasing the strength of current in the conductor or vice-versa.
    (b) Maxwell’s right hand thumb rule indicates the direction of magnetic field for a known direction of current. If the thumb of the right hand points along the direction of current then the curled fingers of that hand gives the direction of the magnetic field due to the current. When thumb is upwards, the curled fingers are anti-clockwise. So, magnetic field is anticlockwise. When thumb is downwards, the curled fingers are clockwise. So, magnetic field is clockwise.
    (c) The two magnetic field lines can never intersect each other because if it does so, then two tangents can be drawn at the point of their intersection which will give two directions of the field from the same point, which is impossible.
  3. Draw the pattern of magnetic field lines around a current carrying straight conductor. How does the strength of the magnetic field produced change :
    (i) with the distance from the conductor ?
    (ii) with an increase in current in a conductor         2014

Ans. The strength of a magnetic field is inversely proportional to the square of the distance from the conductor i.e., strength of an electric field decreases with increase in distance.
(ii) The strength of the magnetic field is directly proportional to the current passing in the wire i.e., strength of the magnetic field increases with the increase in current.

4. What are magnetic field lines ? List two characteristic properties of these lines. [3]

Answer : The lines drawn in a magnetic field along which north magnetic pole moves, are
called magnetic field lines. With the help of a small magnetic compass, the direction of a magnetic field at a point is determined. When the compass is moved along the magnetic line, then the line drawn from the south pole to the north pole indicates the direction of the magnetic field.
The characteristic properties of magnetic field lines are :
(i) The magnetic lines originate from north pole and ends at south pole.
(ii) The magnetic lines do not intersect each other

5. With the help of a diagram of experimental setup describe an activity to show that the force acting on a current carrying conductor placed in a uniform magnetic field increases with increase in the field strength
6. A coil of insulated wire is connected to a galvanometer. What would be seen if a bar magnet with its south pole towards one face of the coil is
(i) moved quickly toward it
(ii) moved quickly away from it
(iii)placed near its one face?
These activities are then repeated with north pole of the magnet. What will be the observations?
(b) Name and define the phenomenon involved in above activities.
(c) Name the rule which can determine the direction of current in each case.
Ans. (a) A coil of insulated wire is connected to a galvanometer and if a bar magnet with its south pole, towards one face of the coil, is
(i) moved quickly towards it, the galvanometer is deflected towards the left.
(ii) moved quickly away from it, the galvanometer is deflected towards the right.
(iii)If the magnet is held stationary inside the coil, the deflection of the galvanometer is zero.
If this activity is repeated with north pole of the magnet :
(i) If the magnet is pushed into the coil, the galvanometer is deflected towards the right.
(ii) If the magnet is withdrawn from the coil, the galvanometer is deflected towards the left.
(iii)If the magnet is held stationary inside the coil, the deflection of the galvanometer is zero.
(b) The phenomenon involved in this activity is ‘Electromagnetic Induction’.
(c) The direction of induced current is determined by ‘Fleming’s Right Hand Rule’.

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