# NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effect of Electric Currents

The Class 10 NCERT Solutions for Science Chapter 13 Magnetic Effect of Electric Currents includes all the intext and exercise questions. Class 10 Science Chapter 13 Magnetic Effect of Electric Currents NCERT questions and answers help students to clear their doubts and to obtain good marks in Class 10 board exam. All the solutions provided in this article are strictly based on the CBSE syllabus and curriculum.

## Class 10 Science Chapter 13 NCERT Questions and Answers

Class 10 Science Chapter 13 Magnetic Effect of Electric Currents NCERT Questions and Answers are prepared by experts with a detailed explanation that will help students complete their assignments & homework. Having a good grasp over CBSE NCERT Solutions for Class 10 Science will further help the students in their preparation for board exams and other competitive exams such as NTSE, Olympiad, etc.

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

Intext Question (Page No. 224)

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

Answer: The compass needle is a small magnet. When the compass needle is brought close to a bar magnet, the magnetic field lines of the compass needle interact with the magnetic field lines of bar magnet, which causes the compass needle to deflect.

Intext Question (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 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 magnetic field at that point.
• The relative strength of magnetic fields is given by 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: This is due to the fact that the resultant force on a north pole at any point can be only in one direction. But if the two magnetic field lines intersect one another, then the resultant force on north pole placed at the point of intersection will be along two directions, which is not possible.

Intext Question (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: (d) is the same at all points.

Intext Question (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?

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.

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.

Intext Question (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 magnetic field and the second finger in the direction of 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 electric motor is based on the magnetic effect of current. A current carrying conductor when placed in a magnetic field experiences force and rotates. The direction of the rotation of the conductor can be determined by Fleming’s Left hand rule.

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

Answer: The split ring reverses the direction of current in the armature coil after every half rotation, i.e., it acts as a commutator. The reversed current reverses the direction of the forces acting on the two arms of the armature after every half rotation. This allows the armature coil to rotate continuously in the same direction.

Intext Question (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.

Intext Question (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: Power plants and AC generators are some of the sources that produce 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

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.

Intext Question (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.

On applying right-hand thumb rule, we find the direction of 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.

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 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 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 resu1t, the resultant magnetic field become 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: When the direction of the current is perpendicular to the direction of the magnetic field is when the force experienced is the largest

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: A few devices in which electric motors are used are:

• Electric fans
• Water pumps
• Mixers
• Washing 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 the coil, current is induced in the coil momentarily as a result the galvanometer deflects in a particular direction momentarily.

(ii) When the bar magnet is withdrawn from inside the coil, current is induced momentarily but in the opposite direction and the galvanometer deflects in the opposite direction momentarily.

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

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, some current will be induced in the coil B. When the current in coil A is changed, some current is induced in the coil B. Due to change in current in coil A, the magnetic field lines linked with coil A and with coil B get changed. This sets up induced current in coil B.

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.

Answer: (i) Maxwell’s Right hand thumb rule: If the current carrying conductor is held in the right hand such that the thumb points in the direction of the current, then the direction of the curl of the fingers will give the direction of the magnetic field.

(ii) Fleming’s left-hand rule: The rule used to determine the force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it is the Fleming’s left hand rule.

(iii) Fleming’s right hand rule: The rule used to determine the current induced in a coil due to its rotation in a magnetic field is the 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?

Principle: An electric generator works on the principle of electromagnetic induction phenomenon. According to it, whenever a coil is rotated between the poles of a magnet, an induced current is set up in the coil, whose direction is given by Fleming’s right-hand rule.

Working: When the axle attached to the two rings is rotated such that the arm AB moves up (and the arm CD moves down) in the magnetic field produced by the permanent magnet. The coil ABCD is rotated clockwise in the arrangement. By applying Fleming’s right-hand rule, the induced currents are set up in these arms along the directions AB and CD. Thus, induced current flows in the direction ABCD. If there are larger numbers of turns in the coil, the current generated in each turn adds up to give a large current through the coil. This means that the current in theexternal circuit flows from B2 to B1. After half a rotation, arm CD starts moving up and AB moving down. As a result, the directions of the induced currents in both the arms change, giving rise to the net induced current in the direction DCBA. The current in the external circuit now flows from B1 to B2. Thus, after every half rotation the polarity of the current in the respective arms changes. Such a current, which changes direction after equal intervals of time, is called an alternating current (abbreviated as AC). This device is called an AC generator.

Question 17: When does an electric short circuit occur?

Answer: If either the insulation of wires used in an electrical circuit is damaged or there is a fault in the appliance, live wire and neutral wire may come in direct contact. As a result, the current in the circuit abruptly rises and short-circuiting occurs.

Question 18: What is the function of an earth wire? Why is it necessary to earth metallic appliances?

Answer: The metallic body of electric appliances is earthed by means of earth wire. Any leakage of electric wire is transferred to the ground by means of earth wire. This prevents the user of the electric appliance from getting electric shocks. This is the reason why it is important for the metallic appliances to be earthed.

### Topics covered under Class 10 Science Chapter 13 Magnetic Effect of Electric Currents

Below we have listed the topics discussed in NCERT Solutions for Class 10 Science Chapter 13. The list gives you a quick look at the different topics and subtopics of this chapter.

### NCERT Solutions for Class 10 Science Chapter 13 – A Brief Discussion

Chapter Overview:  In this chapter you will learn about magnetic field, field lines. This chapter also includes the concept of Force Acting on Current carrying Conductor in a Magnetic Field using Fleming’s Left-Hand Rule, which helps us in the understanding of Electric Motor. Moreover, the chapter also explains electromagnetic induction, electric generator and domestic electric circuits.