Magnetic Effects of Electric Current
1. Which one 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
2. The phenomenon of electromagnetic induction is
(a) The process of charging a body.
(b) The process of generating magnetic field due to a 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 at an electric motor.
3. The device used for producing electric current is called
(a) generator (b) galvenometer
(c) ammeter (d) motor
4. The essential difference between A.C. generator and a D.C. generator is that
(a) A.C. generator has an electromagnet while a D.C. generator has permanent magnet.
(b) D.C. generator will generate a higher voltage
(c) A.C. generator will generate a higher voltage
(d) A.C. generator has slip rings while the D.C. generator has commutator.
5. At the time of short circuit, the current in the circuit:
(a) reduce substantially (b) does not change
(c) increase heavily (d) vary continuously
6. 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 centre of a long circular coil carrying current will be parallel straight line
(d) A wire with green insulation is usually the live wire of an electric supply.
7. List three methods of producing magnetic field.
8. How does a solenoid behave like a magnet? Can you determines the north and south poles of a current carrying solenoid with the help of a bar magnet? Explain.
9. When is the force experienced by a current-carrying conductor placed in magnetic field largest?
10. Imagine that you are sitting in 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?
11. Draw a labelled diagram of an electric motor. Explain its principle and working. What is the function of split ring in an electric motor?
12. Name some devices in which electric motors are used.
13. 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?
14. Two circular coils A and B are placed close to each other. If the current in the coil A is changed, will some current be induced in the coil B? Give reason.
15. State the rule to determine the direction of a (i) magnetic field produced around a straight current carrying conductor (ii) force experienced by a current carrying straight conductor (iii) current induced in a coil due to its rotation in a magnetic
16. Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of brushes?
17. When does an electric short circuit occurs?
18. What is the function of an earth wire? Why is it necessary to earth metallic appliances?
19. Why does a compass needle get deflected when brought near a bar magnet?
20. Draw magnetic field around a bar magnet.
21. List the properties of magnetic lines of force.
22. Why don’t two magnetic lines of force intersect each other?
23. 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.
24. The magnetic field in a given region is uniform. Draw a diagram to represent it.
25. Choose the correct option: The magnetic field inside a long straight solenoid-carrying current
(a) Is zero.
(b) Decrease as we move towards its end.
(c) Increase as we move towards it end.
(d) Is the same all points.
26. Which of the following property of a proton can change while it moves freely in a magnetic field?
(a) mass (b) speed (c) velocity (d) momentum
27. In activity 13.7, how do we think the displacement of rod AB will be affected if (i) current is rod AB is increased, (ii) a stronger horse shoe magnet is used, and (iii) length of the rod AB is increased?
28. 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
29. State Fleming’s left-hand rule.
30. What is the principle of an electric motor?
31. What is the role of the split ring in an electric motor?
32. Explain different ways to induce current in a coil.
33. State the principle of an electric generator.
34. Name some sources of direct current.
35. Which sources produce alternating current?
36. Choose the correct option: A rectangular coil of copper wires is rotated in a magnetic filed. The direction of the induced current changes once in each
(a) two revolutions (c) half revolution
(b) one revolution (d) one-fourth revolution
37. Name two safety measures commonly used in electric circuits and appliances.
38. An electric oven of 2 kW power rating is operated in a domestic electric circuit (220V) that has a current rating of 5.A. What result do you expect? Explain.
39. What precaution should be taken to avoid the overloading of domestic electric circuit?