Magnetic effect of electric current
Q 1. Why does a compass needle get deflected when brought near a bar magnet?
Answer: A compass needle is a small magnet that experiences a force in the magnetic field of a bar magnet. Due to this force, it gets deflected.
Q 2. List the properties of magnetic lines of forces.
Answer: Properties of magnetic lines of forces are :
- Magnetic field lines are closed and continuous curves.
- These lines always begin from the north pole of a magnet and merge into the south pole forming closed curves outside the magnet.
- Inside the magnet, these lines of force originate from its south pole and go towards the north pole.
- These lines are crowded near the poles where the magnetic field is strong and are far apart where the magnetic field is weak.
- These lines never intersect each other
Q 3. Why do not two magnetic lines of forces intersect each other?
Answer:If the magnetic lines of forces intersect, there will be two different directions of magnetic field at that point, which is not possible.
Q 4. Consider a circular loop of wire lying on 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.
Answer: As the current is flowing clockwise. If we are applying the right hand thumb rule to the left side of the loop then the direction of magnetic field lines inside the loop are going into the table while outside the loop they are coming out of the table.
Q 5. The magnetic field in a given region is uniform. Draw a diagram to represent it.
Answer:
Q 6. In Activity 13.7 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?
Answer: (i) When the current in the rod AB is increased, force exerted on the conductor increases, so the displacement of the rod increases.
(ii) When a stronger horse-shoe magnet is used, the magnitude of the magnetic field increases. This increases the force exerted on the rod and the displacement of the rod.(iii) When the length of the rod AB is increased, force exerted on the conductor increases, so the displacement of the rod increases.
Q 7. Name two safety measures commonly used in electric circuits and appliances.
Answer: (i) Earthing and (ii) Electric fuse
Q 8. List three sources of magnetic fields.
Answer: (i) Current carrying conductor, (ii) Electromagnets, (iii) Permanent magnets
Q 9. What precaution should be taken to avoid the overloading of domestic electric circuits?
Answer: The precautions that should be taken to avoid the overloading of domestic circuits are as follows:
(a) Too many appliances should
not be connected to a single socket.
(b) Too many appliances should
not be used at the same time.
(c) Faulty appliances should not be connected in the circuit
(d)
Fuse should be connected in the circuit.
Q 10. When is the force experienced by a current–carrying conductor placed in a magnetic field largest?
Answer: The force experienced by a current carrying conductor is largest when the directions of magnetic field and electric current are perpendicular to each other.
Q 11. Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of magnetic field?
Answer: Fleming's left hand rule is used to determine the direction of magnetic field. The direction of electric current will be from front wall to back wall as it is opposite to the direction of electron. Since the direction of force is towards the right side, by applying Fleming’s left hand rule, we can conclude that the magnetic field inside the chamber is in downward direction.
Q 12. State the rule to determine the direction of a (i) magnetic field produced around a straight conductor-carrying current, (ii) force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it, and (iii) current induced in a coil due to its rotation in a magnetic field.
Answer: (i) Maxwell’s right hand thumb rule is used to determine the direction of magnetic field around the straight conductor carrying current.
(ii) Fleming's left hand rule is used to find the direction of force experienced by a current carrying straight conductor placed in a magnetic field which is perpendicular to it.
(iii) Fleming's right hand rule is used to find the direction of current induced in a coil due to its rotation in a magnetic field.
Q 13. When does an electric short circuit occur?
Answer: When the insulation of live and neutral wires undergoes wear and tear and then touches each other, the current flowing in the circuit increases abruptly. Hence, a short circuit occurs.
Q 14. What is the function of an earth wire? Why is it necessary to earth metallic appliances?
Answer: The main function of earth wire is to protect appliances from sudden damage due to leakage of current.
The metallic body of electric appliances is connected to the earth by means of earth wire so that any leakage of electric current is transferred to the ground. This prevents any electric shock to the user. That is why earthing of the electrical appliances is necessary.
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