1. Name the scientist who showed that electricity and magnetism
are related.
Ans. Oersted showed that electricity and magnetism were related
phenomena. His research later created technologies such as the
radio, television and fiber optics.
2. List the properties of magnetic lines of force.
3. Why don’t two magnetic lines of force intersect each other?
Ans. If field lines of a magnetic field are intersected each other at a point, it indicates the compass needle would point towards two directions, which is not possible.
4. 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. If the current is flowing clockwise and if we are applying right-hand thumb
the rule then the direction of magnetic field lines inside the loop is going into the table while outside the loop they are coming out of the table.
5. The magnetic field in a given region is uniform. Draw a diagram to represent it.
Ans. ⇶ B
6. Choose the correct option. The magnetic field 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.
7. 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. (c) velocity (d) momentum.
8. A positively charged particle says an alpha particle projected towards the west is deflected toward the north by a magnetic field. The direction of the magnetic field is :
10. State Fleming’s left-hand rule.
Ans. According to Fleming’s left-hand rule, stretch the thumb, forefinger and middle finger of your left hand such that they are mutually perpendicular. If the first finger points in the direction of the magnetic field and the second finger in the direction of the current, then the thumb will point in the direction of motion or the force acting on the conductor.
11. What is the principle of an electric motor? What is the function of a split ring in an electric motor?
Ans. An electric motor is a rotating device that converts electrical energy to mechanical energy. The electric motor is used as an important component in electric fans, refrigerators, mixers, washing machines, computers, MP3 players, etc.
The split ring acts as a commutator, a device that reverses the direction of flow of current through a circuit in the motor.
12. What is the role of the split ring in an electric motor?
Ans. In electric motors, the split ring acts as a commutator which is a device that reverses the direction of flow of current through a circuit.
13. Explain different ways to induce a current in a coil.
Ans. (i)By changing the magnetic field - as the current in the primary coil changes, the magnetic field associated with it also changes. Thus the magnetic field lines around the secondary coil also change. Hence the change in magnetic field lines associated with the secondary coil is the cause of induced electric current in it.
(ii) By moving coil in a magnetic field or moving a magnet towards a coil sets up a current in the circuit due to change in a magnetic field.
14. State the principle of an electric generator. What is the function of the brushes?
Ans. In an electric generator, mechanical energy is used to rotate a conductor in a magnetic field to produce electricity.
Brushes are connected to the galvanometer to show the flow of current in the given external circuit.
15. Name some sources of direct current.
Ans. Battery and D.C generator are the two sources of direct current.
16. Which sources produce alternating current?
Ans. A.C generator.
17. Choose the correct option. A rectangular coil of copper wires is rotated in a magnetic field. The direction of the induced current changes once in each
(a) two revolutions (b) one revolution (c) half revolution (d) one-fourth revolution.
Ans. (c) half revolution
18. Name two safety measures commonly used in electric circuits and appliances.
Ans. The Earth wire and Fuse are the two safety measures.
19. An electric oven of 2 kW power rating is operated in a domestic electric circuit (220 V) that has a current rating of 5 A. What result do you expect? Explain.
Ans. The power rating of the oven is 2kW means 2000W and volt is 220 then I will be: I= P/V = 2000/220 = 200/22 = 9.09A which is more than 5A. So the fuse will get broken and the circuit will get open.
18. What precaution should be taken to avoid the overloading of domestic electric circuits?
Ans. We should use a fuse in a circuit which prevents damage to the appliances and the circuit due to overloading.
19. Which of the following correctly describes the magnetic field near a long straight wire?
(a) The field consists of straight lines perpendicular to the wire. (b) The field consists of straight lines parallel to the wire. (c) The field consists of radial lines originating from the wire. (d) The field consists of concentric circles centered on the wire.
Ans. According to right-hand thumb rule (d), The field consists of concentric circles centered on the wire.
20. The phenomenon of electromagnetic induction is
(a) the process of charging a body.
(b) the process of generating a magnetic field due to current passing through a coil.
(c) producing induced current in a coil due to relative motion between a magnet and the coil.
(d) the process of rotating a coil of an electric motor.
Ans. (c) producing induced current in a coil due to relative motion between a magnet and the coil.
21. The device used for producing electric current is called a
(a) generator. (b) galvanometer. (c) ammeter. (d) motor.
Ans. (a) generator.
22. The essential difference between an AC generator and a DC generator is that
(a) AC generator has an electromagnet while a DC generator has a permanent magnet.
(b) DC generator will generate a higher voltage.
(c) AC generator will generate a higher voltage.
(d) AC generator has slip rings while the DC generator has a commutator.
Ans. (d) AC generator has slip rings while the DC generator has a commutator.
23. At the time of the short circuit, the current in the circuit
(a) reduces substantially. (b) does not change. (c) increases heavily. (d) vary continuously.
Ans. (c) increases heavily
24. State whether the following statements are true or false.
(a) An electric motor converts mechanical energy into electrical energy.
(b) An electric generator works on the principle of electromagnetic induction.
(c) The field at the center of a long circular coil carrying current will be parallel straight lines.
(d) A wire with green insulation is usually the live wire of electric supply.
Ans.(i) F (ii) T (iii) T (iv) F
25. List three sources of magnetic fields.
Ans. Three sources of the magnetic field are (i) Electromagnet (ii) Current carrying conductor (iii) Current carrying solenoid.
26. How does a solenoid behave like a magnet? Can you determine the north and south poles of a current-carrying solenoid with the help of a bar magnet? Explain.
Ans. (i) The pattern of the magnetic field lines around a current-carrying solenoid is the same as the pattern of the field with the magnetic field around a bar magnet.
(ii) One end of the solenoid behaves as a magnetic north pole, while the other behaves as the south pole.
(iii) The field lines inside the solenoid are in the form of parallel straight lines. This indicates that the magnetic field is the same at all points inside the solenoid.
27. When is the force experienced by a current-carrying conductor placed in a magnetic field largest?
Ans.When the direction of current is at right angles to the direction of the magnetic field.
28. Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from the back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of the magnetic field?
Ans. The direction of the magnetic field is Downwards according to Left-hand fleming's rule.
29. Name some devices in which electric motors are used.
Ans. The electric motor is used as an important component in electric fans, refrigerators, mixers, washing machines, computers, MP3 players, etc.
30. A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is
(i) pushed into the coil, (ii) withdrawn from inside the coil, (iii) held stationary inside the coil?
Ans. (i) Deflection in the needle of the galvanometer, say to the right.
(ii) Deflection in the needle of the galvanometer, say to the left
(iii) Zero deflection.
31. Two circular coils A and B are placed closed to each other. If the current in the coil A is changed, will some current be induced in coil B? Give reason.
Ans. A potential difference is induced in the coil-B (Secondary coil) whenever the electric current through the coil–A (primary coil)is changing. As the current in the first coil changes, the magnetic field associated with it also changes. Thus the magnetic field lines around the secondary coil also change. Hence the change in magnetic field lines associated with the secondary coil is the cause of induced electric current in it. This process, by which a changing magnetic field in a conductor induces a current in another conductor, is called electromagnetic induction.
32. 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.
Ans. (i) Right-hand thumb rule.
(ii) Fleming's left-hand rule.
(iii) Fleming's right-hand rule.
33. When does an electric short circuit occur?
Ans. Overloading can occur when the live wire and the neutral wire come into direct contact. This occurs when the insulation of wires is damaged or there is a fault in the appliance. In such a situation, the current in the circuit abruptly increases. This is called short-circuiting.
34. What is the function of an earth wire? Why is it necessary to earth metallic appliances?
Ans. The earth wire, which has insulation of green colour, is usually connected to a metal plate deep in the earth near the house. This is used as a safety measure, especially for those appliances that have a metallic body, for example, electric press, toaster, table fan, refrigerator, etc.
The metallic body is connected to the earth wire, which provides a low-resistance conducting path for the current. Thus, it ensures that any leakage of current to the metallic body of the appliance keeps its potential to that of the earth, and the user may not get a severe electric shock.
are related.
Ans. Oersted showed that electricity and magnetism were related
phenomena. His research later created technologies such as the
radio, television and fiber optics.
2. List the properties of magnetic lines of force.
Ans. Two properties of magnetic lines of force are :
(i) Magnetic lines of force never intersect with each other.
(ii) They are closed and continuous curved. 3. Why don’t two magnetic lines of force intersect each other?
Ans. If field lines of a magnetic field are intersected each other at a point, it indicates the compass needle would point towards two directions, which is not possible.
4. 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. If the current is flowing clockwise and if we are applying right-hand thumb
the rule then the direction of magnetic field lines inside the loop is going into the table while outside the loop they are coming out of the table.
5. The magnetic field in a given region is uniform. Draw a diagram to represent it.
Ans. ⇶ B
6. Choose the correct option. The magnetic field 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.
7. 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. (c) velocity (d) momentum.
8. A positively charged particle says an alpha particle projected towards the west is deflected toward the north by a magnetic field. The direction of the magnetic field is :
(a) Upward (b) Downward (c) Towards south (d) Towards east.
Ans. The direction of alpha particles is towards the west means the direction of current is towards the west and the direction of deflection is towards the north, therefore according to Fleming's left-hand rule the direction of the magnetic field will be upward.
9. 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 the current in rod AB is increased the displacement of the rod will more.
(ii) If a stronger horseshoe magnet is used, due to strong force-deflection will be more.
(iii) If The length of the rod AB is increased, the deflection will be also more
9. 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 the current in rod AB is increased the displacement of the rod will more.
(ii) If a stronger horseshoe magnet is used, due to strong force-deflection will be more.
(iii) If The length of the rod AB is increased, the deflection will be also more
10. State Fleming’s left-hand rule.
Ans. According to Fleming’s left-hand rule, stretch the thumb, forefinger and middle finger of your left hand such that they are mutually perpendicular. If the first finger points in the direction of the magnetic field and the second finger in the direction of the current, then the thumb will point in the direction of motion or the force acting on the conductor.
11. What is the principle of an electric motor? What is the function of a split ring in an electric motor?
Ans. An electric motor is a rotating device that converts electrical energy to mechanical energy. The electric motor is used as an important component in electric fans, refrigerators, mixers, washing machines, computers, MP3 players, etc.
The split ring acts as a commutator, a device that reverses the direction of flow of current through a circuit in the motor.
12. What is the role of the split ring in an electric motor?
Ans. In electric motors, the split ring acts as a commutator which is a device that reverses the direction of flow of current through a circuit.
13. Explain different ways to induce a current in a coil.
Ans. (i)By changing the magnetic field - as the current in the primary coil changes, the magnetic field associated with it also changes. Thus the magnetic field lines around the secondary coil also change. Hence the change in magnetic field lines associated with the secondary coil is the cause of induced electric current in it.
(ii) By moving coil in a magnetic field or moving a magnet towards a coil sets up a current in the circuit due to change in a magnetic field.
14. State the principle of an electric generator. What is the function of the brushes?
Ans. In an electric generator, mechanical energy is used to rotate a conductor in a magnetic field to produce electricity.
Brushes are connected to the galvanometer to show the flow of current in the given external circuit.
15. Name some sources of direct current.
Ans. Battery and D.C generator are the two sources of direct current.
16. Which sources produce alternating current?
Ans. A.C generator.
17. Choose the correct option. A rectangular coil of copper wires is rotated in a magnetic field. The direction of the induced current changes once in each
(a) two revolutions (b) one revolution (c) half revolution (d) one-fourth revolution.
Ans. (c) half revolution
18. Name two safety measures commonly used in electric circuits and appliances.
Ans. The Earth wire and Fuse are the two safety measures.
19. An electric oven of 2 kW power rating is operated in a domestic electric circuit (220 V) that has a current rating of 5 A. What result do you expect? Explain.
Ans. The power rating of the oven is 2kW means 2000W and volt is 220 then I will be: I= P/V = 2000/220 = 200/22 = 9.09A which is more than 5A. So the fuse will get broken and the circuit will get open.
18. What precaution should be taken to avoid the overloading of domestic electric circuits?
Ans. We should use a fuse in a circuit which prevents damage to the appliances and the circuit due to overloading.
19. Which of the following correctly describes the magnetic field near a long straight wire?
(a) The field consists of straight lines perpendicular to the wire. (b) The field consists of straight lines parallel to the wire. (c) The field consists of radial lines originating from the wire. (d) The field consists of concentric circles centered on the wire.
Ans. According to right-hand thumb rule (d), The field consists of concentric circles centered on the wire.
20. The phenomenon of electromagnetic induction is
(a) the process of charging a body.
(b) the process of generating a magnetic field due to current passing through a coil.
(c) producing induced current in a coil due to relative motion between a magnet and the coil.
(d) the process of rotating a coil of an electric motor.
Ans. (c) producing induced current in a coil due to relative motion between a magnet and the coil.
21. The device used for producing electric current is called a
(a) generator. (b) galvanometer. (c) ammeter. (d) motor.
Ans. (a) generator.
22. The essential difference between an AC generator and a DC generator is that
(a) AC generator has an electromagnet while a DC generator has a permanent magnet.
(b) DC generator will generate a higher voltage.
(c) AC generator will generate a higher voltage.
(d) AC generator has slip rings while the DC generator has a commutator.
Ans. (d) AC generator has slip rings while the DC generator has a commutator.
23. At the time of the short circuit, the current in the circuit
(a) reduces substantially. (b) does not change. (c) increases heavily. (d) vary continuously.
Ans. (c) increases heavily
24. State whether the following statements are true or false.
(a) An electric motor converts mechanical energy into electrical energy.
(b) An electric generator works on the principle of electromagnetic induction.
(c) The field at the center of a long circular coil carrying current will be parallel straight lines.
(d) A wire with green insulation is usually the live wire of electric supply.
Ans.(i) F (ii) T (iii) T (iv) F
25. List three sources of magnetic fields.
Ans. Three sources of the magnetic field are (i) Electromagnet (ii) Current carrying conductor (iii) Current carrying solenoid.
26. How does a solenoid behave like a magnet? Can you determine the north and south poles of a current-carrying solenoid with the help of a bar magnet? Explain.
Ans. (i) The pattern of the magnetic field lines around a current-carrying solenoid is the same as the pattern of the field with the magnetic field around a bar magnet.
(ii) One end of the solenoid behaves as a magnetic north pole, while the other behaves as the south pole.
(iii) The field lines inside the solenoid are in the form of parallel straight lines. This indicates that the magnetic field is the same at all points inside the solenoid.
27. When is the force experienced by a current-carrying conductor placed in a magnetic field largest?
Ans.When the direction of current is at right angles to the direction of the magnetic field.
28. Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from the back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of the magnetic field?
Ans. The direction of the magnetic field is Downwards according to Left-hand fleming's rule.
29. Name some devices in which electric motors are used.
Ans. The electric motor is used as an important component in electric fans, refrigerators, mixers, washing machines, computers, MP3 players, etc.
30. A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is
(i) pushed into the coil, (ii) withdrawn from inside the coil, (iii) held stationary inside the coil?
Ans. (i) Deflection in the needle of the galvanometer, say to the right.
(ii) Deflection in the needle of the galvanometer, say to the left
(iii) Zero deflection.
31. Two circular coils A and B are placed closed to each other. If the current in the coil A is changed, will some current be induced in coil B? Give reason.
Ans. A potential difference is induced in the coil-B (Secondary coil) whenever the electric current through the coil–A (primary coil)is changing. As the current in the first coil changes, the magnetic field associated with it also changes. Thus the magnetic field lines around the secondary coil also change. Hence the change in magnetic field lines associated with the secondary coil is the cause of induced electric current in it. This process, by which a changing magnetic field in a conductor induces a current in another conductor, is called electromagnetic induction.
32. 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.
Ans. (i) Right-hand thumb rule.
(ii) Fleming's left-hand rule.
(iii) Fleming's right-hand rule.
33. When does an electric short circuit occur?
Ans. Overloading can occur when the live wire and the neutral wire come into direct contact. This occurs when the insulation of wires is damaged or there is a fault in the appliance. In such a situation, the current in the circuit abruptly increases. This is called short-circuiting.
34. What is the function of an earth wire? Why is it necessary to earth metallic appliances?
Ans. The earth wire, which has insulation of green colour, is usually connected to a metal plate deep in the earth near the house. This is used as a safety measure, especially for those appliances that have a metallic body, for example, electric press, toaster, table fan, refrigerator, etc.
The metallic body is connected to the earth wire, which provides a low-resistance conducting path for the current. Thus, it ensures that any leakage of current to the metallic body of the appliance keeps its potential to that of the earth, and the user may not get a severe electric shock.
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