13.a) What is the principle of electric motor.
b)What is the function of split rings in an electric motor?
c)What is a solenoid?
d)A compass needle shows deflection when brought near a current carrying conductor. Why?
1
e)Why two Magnetic field line never intersect each other?
Answers
Answer:
d is the right is the right
Answer:
Why does a compass needle get deflected when brought near a bar magnet?
Ans. A compass needle is a small bar magnet with north and south pole. The compass needle deflects due to repulsion/attraction with the bar magnet.
2. Draw magnetic field lines around a bar magnet.
Ans.
3. List the properties of magnetic lines of force.
Ans. Properties of magnetic field lines of force:
(i) Magnetic field lines travel from N-pole of magnet towards 5-pole, outside the magnet and from S-pole to N-pole inside the magnet.
(ii) The strength of magnet/magnetic field is given by how close the field lines are if the field lines are closer magnet is stronger.
(iii) No two magnetic field lines ever intersect each other.
4. Why don’t two magnetic lines of force intersect each other?
Ans. The magnetic field lines never intersect each other as an intersection of the field lines means the magnetic field at that point has two directions, which is not possible because the resultant force on a pole (north/south) at any point can only be in one direction.
5. Consider a circular loop of wire lying in the plane of. the table. Let the current pass through the loop clockwise. Apply the right hand rule to find out the direction of the magnetic field inside and outside the loop.
Ans.
6. The magnetic field in a given region is uniform. Draw a diagram to represent it.
Ans.
The magnetic field in a given region is uniform can be represented by showing parallel lines at equidistance.
7. Choose the correct option.
The magnetic Meld inside a long straight solenoid-carrying current
(a) is zero.
(b) decreases as we move towards its end.
(c) increases as we move towards its end.
(d) is the same at all points.
Ans. (d) is the same at all points.
8. Which of the following property of a proton can change while it moves freely in a magnetic field?
(There may be more than one correct answer).
(a) mass
(b) speed
(c) velocity
(d) momentum
Ans. Velocity and momentum
9. In activity 13.7 (on page 234) how do we think the displacement of rod AB will be affected if
(i) current in rod AB is increased
(ii) a stronger horse-shoe magnet is used and
(iii) length of the rod AB is increased.
Ans. (i) If current in rod AB is increased its displacement will increase.
(ii) If a stronger horse-shoe magnet is used then the displacement of rod AB will increase.
(iii) If the length of the rod AB is increased force acting on it will increase and the displacement of the rod also increases.
10. A positively charged particle (alpha-particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is
(a) towards south
(b) towards east
(c) downward
(d) upward
Ans. (c) downward
11. State Fleming’s left hand rule.
Ans. According to this rule, stretch the thumb, fore-finger and middle finger of left hand such that they are mutually perpendicular. If the middle finger points in the direction of the magnetic field, the fore-finger points in the direction of flow of current, then the thumb points in the direction of motion i.e., force acting on the conductor.
of current in both arms is opposite. As per Fleming’s left hand rule, the force acting on arm AB pushes it down while the force acting on CD pushes it upwards. Thus, the coil and the axle rotate anticlockwise. Due to action of split ring commutator at half rotation, split rings P and Q change their contacts with brushes. Now P makes contact with Y and Q with X. As a result, current begins to flow in coil along DCBA, As a result now arm AB is being pushed upward and arm CD downward by the magnetic force. So coil rotate half a turn more in the same direction. This reversing of current direction is repeated at each half rotation and so the coil continues to rotate in the same direction. The split ring helps in changing the direction of the current.
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Explanation:
What is the function of an earth wire? Why is it necessary to earth metallic appliances?
Ans. The earth wire is connected as a safety measure with all electrical appliances that have metallic body e.g., microwave, electric press, toaster, geyser, cooler, AC, etc. The earth wire provides a low resistance conducting path for electric current. If there is any leakage of current then the user would not get any