# NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current

NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current includes answers of intext & exercise questions. All these NCERT solutions are prepared by expert teachers with detailed explanations of every important topic. It is important for the students to go through these NCERT solutions to get knowledge of the type of question asked on Magnetic Effects of Electric Current chapter.

## NCERT Solutions for Class 10 Science Chapter 13 Intext Questions

PAGE NO. 224

Question 1: Why does a compass needle get deflected when brought near a bar magnet?

Answer: Magnetic compass needle and bar magnet both have a magnetic field. When they brought near to each other, these magnetic fields interact with each other giving deflection in the needle.

PAGE NO. 228

Question 1: Draw magnetic field lines around a bar magnet.

Question 2: List the properties of magnetic lines of force.

Answer: Properties of magnetic lines of force (also known as magnetic field lines) are listed below:

• Outside the magnet, the magnetic field lines are directed from N-pole of the magnet towards S-pole. However, inside a magnet the field lines are directed from S-pole to N-pole. Thus, magnetic field lines form a close loop.
• The magnetic field line at any point points in the direction of the magnetic field at that point.
• The relative strength of magnetic fields is given by the degree of closeness of the field lines. The magnetic field is strong in the region where the field lines are crowded.
• No two magnetic field lines can ever intersect with each other.

Question 3: Why don’t two magnetic lines of force intersect each other?

Answer: No two field-lines are found to cross each other. If they did, it would mean that at the point of intersection, the compass needle would point towards two directions, which is not possible.

PAGE NO. 229-230

Question 1: 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.

Answer: The magnetic field lines have been shown in Figure given below. As per right- hand rule, we find that inside the loop, the magnetic field lines are directed perpendicular to the plane of paper in the inward direction. Outside the loop, magnetic field lines are directed out of the plane of paper.

Question 2: The magnetic field in a given region is uniform. Draw a diagram to represent it.

Answer: The uniform magnetic field is represented by parallel, equidistant lines of equal length as shown in Figure.

Question 3: 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.

Answer 3: (d) is the same at all points.

PAGE NO. 231-232

Question 1: 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

Answer: (c) Velocity and (d) Momentum

Question 2: 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?

(i) If the current in rod AB is increased, the displacement will also increase.

(ii) If we use a stronger horse-shoe magnet then the displacement of rod AB will increase.

(iii) lf length of the rod is increased, the force acting on it will increase and, hence, displacement of the rod increases.

Question 3: 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

In accordance with Fleming’s left-hand rule, the direction of magnetic field is vertically upward.

PAGE NO. 233

Question 1: State Fleming’s left-hand rule.

Answer: 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.

Question 2: What is the principle of an electric motor?

Answer: The working principle of an electric motor is based on the magnetic effect of current. A current-carrying loop experiences a force and rotates when placed in a magnetic field. The direction of rotation of the loop is given by Fleming’s left-hand rule.

Question 3: What is the role of the split ring in an electric motor?

Answer: The split ring in the electric motor acts as a commutator. The commutator reverses the direction of current flowing through the coil after each half rotation of the coil. Due to this reversal of the current, the coil continues to rotate in the same direction.

PAGE NO. 236

Question 1: Explain different ways to induce current in a coil.

Answer: Different ways to induce current in a coil are as given below:

• If a magnetic field is changed around a coil then an induced current is set up in the coil. It can be done by taking a bar magnet and bringing it closer to the coil or taking it away from the coil.
• If a coil is moved in a magnetic field, then again, an induced current is set up in the coil.
• If a coil is rotated in a uniform magnetic field, it may also produce an induced current in the coil.

PAGE NO. 237

Question 1: State the principle of an electric generator.

Answer: An electric generator is based on the principle of electromagnetic induction. When a rectangular coil is rotated in a uniform magnetic field, an induced voltage is generated between the ends of the coil.

Question 2: Name some sources of direct current.

Answer: Some sources of direct current are a cell, a battery and a D.C. generator.

Question 3: Which sources produce alternating current?

Answer: A.C. generator and invertors (used in house for emergency power supply) produces alternating current.

Question 4: 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

Answer: (c) When a rectangular coil of copper wire is rotated in a magnetic field, the direction of the induced current changes once in each half revolution.

PAGE NO. 238

Question 1: Name two safety measures commonly used in electric circuits and appliances.

• Use of earth wire and proper earthing.
• Use of fuse (nowadays fuse wire is replaced by MCB).

Question 2: 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.

Answer: Power rating of electric oven P = 2 kW = 2000 W,
Supply voltage, V=220V
So, the current drawn by electric oven

As the current rating of domestic electric circuit is only 5 A and the oven draws a current 9 A, which is more than the current rating, hence the circuit will be damaged due to overheating/overloading.

Question 3: 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:

• Too many appliances should not be connected to a single socket.
• Too many appliances should not be used at the same time.
• Faulty appliances should not be connected in the circuit.
• Fuse should be connected in the circuit.

## NCERT Solutions for Class 10 Science Chapter 13 Exercise Questions

Question 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.

Answer: (d) The field consists of concentric circles centred on the wire.

The field consists of concentric circles centred on the wire. On applying right-hand thumb rule, we find the direction of the magnetic field. The field is in the form of concentric circles centred on the wire carrying current.

Hence, the option (d) is correct.

Question 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.

Answer: (c) producing induced current in a coil due to relative motion between a magnet and the coil.

In electromagnetic induction phenomenon an induced current begins to flow in a coil whenever there is change in magnetic field in and around a coil.

Hence, the option (c) is correct.

Question 3: The device used for producing electric current is called a

(a) generator.
(b) galvanometer
(c) ammeter.
(d) motor

An A.C. generator is the device used for producing an electric current. Hence, the option (a) is correct.

Question 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

Answer: (d) AC generator has slip rings while the DC generator has a commutator

Question 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.

At the time of short circuiting the live wire and the neutral wire come into direct contact. As a result, the current in the circuit abruptly increases. Hence, the option (c) is correct.

Question 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.

(a) False
(b) True
(c) True
(d) False

Question 7: List three sources of magnetic fields.

Answer: Three methods of producing magnetic field are as follows:

• Magnetic field can be produced by placing a permanent bar magnet or a horse-shoe magnet at the place, where the magnetic field is required.
• Magnetic field is produced around a current-carrying straight conductor or a current-carrying circular coil.
• A very good method to produce magnetic field is due to the flow of current in a solenoid.

Question 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.

Answer: When current is passed through a solenoid coil, magnetic field produced due to each turn of solenoid coil is in the same direction. As a result, the resultant magnetic field becomes very strong and uniform. The field lines inside the solenoid are in the form of parallel straight lines along the axis of solenoid. Thus, the solenoid behaves like a bar magnet. One end of solenoid behaves as a magnetic North pole while the other end behaves as the South Pole.

We can determine the magnetic poles formed in a solenoid. The end of the current-carrying solenoid, which attracts North Pole but repels South Pole of a bar magnet, is behaving as south magnetic pole. The other end, which attracts South Pole of a bar magnet but repels the North Pole, is behaving as north magnetic pole. It is because like poles repel but unlike poles attract each other.

Question 9: 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 placed in a magnetic field is largest when the current-carrying conductor is placed in a direction perpendicular to that of magnetic field.

Question 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?

Answer: An electron beam moving horizontally from back wall towards the front wail is equivalent to a current flowing in the opposite direction (i.e., from front wall towards the back wall). The deflection of electron beam as seen by observer is to his right side and is shown in Figure. On applying Fleming’s left-hand rule we find that the magnetic field is acting in vertically downward direction.

Question 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?

Principle: A current-carrying conductor, when placed in a magnetic field, experiences a force. If the direction of the field and that of the current are mutually perpendicular then force acting on the conductor will be perpendicular to both and will be given by Fleming’s left-hand rule. Due to this force the conductor begins to move.

Working: Current in the coil ABCD enters from the source battery through conducting brush X and flows back to the battery through brush Y. The current in arm AB of the coil flows from A to B. In arm CD it flows from C to D, that is, opposite to the direction of current through arm AB. We find that the force acting on arm AB pushes it downwards while the force acting on arm CD pushes it upwards. Thus, the coil and the axle O, mounted free to turn about an axis, rotate anti-clockwise. At half rotation, Q makes contact with the brush X and P with brush Y. Therefore, the current in the coil gets reversed and flows along the path DCBA. The reversal of current also reverses the direction of force acting on the two arms AB and CD. Thus, the arm AB of the coil that was earlier pushed down is now pushed up and the arm CD previously pushed up is now pushed down. Therefore, the coil and the axle rotate half a turn more in the same direction. The reversing of the current is repeated at each half rotation, giving rise to a continuous rotation of the coil and to the axle.

Question 12: Name some devices in which electric motors are used.

Answer: Electric motors are used in all such devices where we want to convert electrical energy into mechanical energy so as to drive that machine. In our houses, electric motors are being fitted in electric fans, coolers, air conditioners, mixer grinders, washing machines, refrigerators, juicers, computers etc. In factories, motors are used in almost all machines.

Question 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?

Answer: A current induces in a solenoid if a bar magnet is moved relative to it. This is the principle of electromagnetic induction.

(i) When a bar magnet is pushed into a coil of insulated copper wire, a current is induced momentarily in the coil. As a result, the needle of the galvanometer deflects momentarily in a particular direction.

(ii) When the bar magnet is withdrawn from inside the coil of the insulated copper wire, a current is again induced momentarily in the coil in the opposite direction. As a result, the needle of the galvanometer deflects momentarily in the opposite direction.

(iii) When a bar magnet is held stationary inside the coil, no current will be induced in the coil. Hence, galvanometer will show no deflection.

Question 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.

Answer: Yes, a current is induced in the coil B.  When the current in the coil A is changed, the magnetic field associated with it also changes. As coil B is placed close to A, hence magnetic field lines around this coil also change. Due to change in magnetic field lines associated with coil B, an induced current is also induced in it.

Question 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.

(i) Maxwell’s right-hand thumb rule
(ii) Fleming’s left-hand rule
(iii) Fleming’s right-hand rule

Question 16: Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of brushes?