NCERT Solutions for Class 10th Science
Chapter 13 – MAGNETIC EFFECTS OF ELECTRIC CURRENT
(Complete Downloadable Chapter Solution PDF file is at the bottom of the page)
Q.1 Why does a compass needle get deflected when brought near a bar magnet?
Ans A compass needle is, in fact, a small bar magnet with its ends pointing approximately towards north and south directions. It does get deflected due to the interaction of its magnetic lines with that of the bar magnet.
Q.2 Draw magnetic field lines around a bar magnet.
Q.3 List the properties of magnetic lines of force.
Ans Properties of magnetic lines of force:
1) Field lines emerge from north pole and merge at the south pole. But inside the magnet, the direction of field lines is from its south pole to its north pole.
2) Magnetic field lines are closed curves.
3) The relative strength of the magnetic field is shown by the degree of closeness of the field lines. i.e.the field is stronger where the field lines are crowded.
4) No two field lines intersect each other.
Q.4 Why don’t two magnetic lines of force intersect each other?
Q.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 By applying right-hand rule one can see that, in both the cases magnetic field will be perpendicular to the plane of table.
Inside the loop: The direction of magnetic field is downward i.e. going into the table.
Outside the loop: The direction of magnetic field is upward i.e. coming out of the table.
Q.6 The magnetic field in a given region is uniform. Draw a diagram to represent it.
Q.7 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.
Q.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
Q.9 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?
Q.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
Q.11 State Fleming’s left-hand rule.
Q.12 What is the principle of an electric motor?
Q.13 What is the role of the split ring in an electric motor?
Q.14 Explain different ways to induce current in a coil.
Q.15 State the principle of an electric generator.
Q.16 Name some sources of direct current.
Ans 1) DC Generator 2) Dry cell
Q.17 Which sources produce alternating current?
Ans 1) Power house generators 2) AC Dynamo
Q.18 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
Q.19 Name two safety measures commonly used in electric circuits and appliances.
Q.20 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.
Q.21 What precaution should be taken to avoid the overloading of domestic electric circuits?
EXERCISES
Q.1 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 centred on the wire.
Ans (d) The field consists of concentric circles centred on the wire.
Q.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 of an electric motor.
Ans (c) producing induced current in a coil due to relative motion between a magnet and the coil.
Q.3 The device used for producing electric current is called a
(a) generator.
(b) galvanometer.
(c) ammeter.
(d) motor.
Ans (a) generator.
Q.4 The essential difference between an AC generator and a DC generator is that
(a) AC generator has an electromagnet while a DC generator has 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.
Q.5 At the time of short circuit, the current in the circuit
(a) reduces substantially.
(b) does not change.
(c) increases heavily.
(d) vary continuously.
Ans (c) increases heavily
Q.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 lines.
(d) A wire with a green insulation is usually the live wire of an electric supply.
Ans (a) An electric motor converts mechanical energy into electrical energy. (F)
Correct: An electric motor converts electrical energy into mechanical energy.
Q.7 List three methods of producing magnetic fields.
Q.8 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.
Q.9 When is the force experienced by a current–carrying conductor placed in a magnetic field largest?
Q.10 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?
Q.11 Draw a labelled diagram of an electric motor. Explain its principle and working. What is the function of a split ring in an electric motor?
Q.12 Name some devices in which electric motors are used.
Q.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?
Q.14 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 the coil B? Give reason.
Q.15 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.
Q.16 Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of brushes?
Q.17 When does an electric short circuit occur?
Ans Short circuit may be defined as an abrupt increase of the current in the circuit. It may 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 resistance of the circuit becomes very low and hence the current in the circuit abruptly increases as per ohm’s law. This may lead to spark in the circuit.
Q.18 What is the function of an earth wire? Why is it necessary to earth metallic appliances?