Chapter 13 of NCERT Class 10 Science is Magnetic effects of Electric Current. In this chapter, you will learn about the behavior of magnetic field lines and force on conductors placed in a magnetic field. This chapter has a total of 18 questions in this chapter that are going to help you understand the working of different machines like, electric motor and generator with the help of hand rules.
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NCERT Solution for Class 10 Science Chapter 13 Magnetic Effects of Electric Current PDF
Why does a compass needle get deflected when brought near a bar
A compass needle act tiny bar magnet having ends pointing towards north called North Pole and other end towards south called South Pole.
Draw the magnetic field lines around a bar magnet.
Solution: Refer pdf.
List the properties of magnetic lines of force.
1. Field lines emerges from North Pole.
2. Field lines merge at South Pole.
3. Inside the magnet, direction of field lines is from South Pole to North Pole.
4. No two field lines cross each other.
Why don’t two magnetic lines of force intersect each other?
No two field lines cross each other. If they did, it would mean that at that point of intersection the compass needle will point out at two directions, which is impossible.
Consider a circular loop of wire lying in plane of table. Let the current pass
through the loop clockwise. Apply the right hand rule to find out the
direction of magnetic field inside and outside the loop.
In above figure, current if flowing in clockwise manner. If we apply right hand rule to left side of loop then magnetic field lines are going towards the table inside the loop and direction of magnetic field lines are coming out of the table outside the loop. The direction of magnetic field lines is vice versa in right side of loop.
The magnetic field in a given region is uniform. Draw a diagram to
Solution: Refer pdf.
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
(d) Is the same at all points.
Exercise No: 13.4
Which of the following property of a proton can change while it moves
freely in a magnetic field?
Velocity and momentum.
In Activity 13.7(page: 230), 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) Current in the rod AB is increased then rod will get deflected with larger force.
(ii) If a stronger magnet is used then it will increase magnetic field and rod gets deflected with larger force.
(iii) Increase in length of rod will result increase in force on the rod.
A positively-charged particle (alpha-particle) projected towards west is
deflected towards north by a magnetic field. The direction of magnetic field
(a) towards south (b) towards east
(c) downward (d) upward
State Fleming’s left-hand rule.
According to Fleming’s left-hand rule, if we stretch the thumb , forefinger and middle finger of our left hand such that they become mutually perpendicular then, thumb will point in the direction of motion or force , first finger points in the direction of magnetic field and second finger in direction of current.
What is the principle of an electric motor?
An electric motor is a rotating device that converts electrical energy into mechanical energy. The principle of working of an electric motor is based on magnetic effect of electric current. A current-carrying loop experiences a force and rotates when placed in a magnetic field.
What is the role of the split ring in an electric motor?
The split ring in an electric motor is used to reverse the direction of current flowing in coil after every half rotation of coil. This is done so that the coil will rotate in same direction. Split ring is also known as commentator.
Exercise No: 13.6
Explain different ways to induce current in a coil.
Following are the ways to induce current in a coil –
(i) By changing the magnetic field lines associated with secondary coil.
(ii) By moving a magnet towards a coil which is placed in coil circuit.
(iii) By rapidly to and fro moving a coil between two pole of horse-shoe magnet.
Exercise No: 13.7
State the principle of an electric generator.
The principle of an electric generator is based on electromagnetic induction. When the magnetic field around a conductor is varied then a current is induced in circuit. Electricity is generated by rotating coil inside magnetic field.
Name some sources of direct current.
Cell, battery, DC generators are sources of direct current.
Which sources produce alternating current?
AC generators, power stations or power plants.
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
(c) Half revolution
Exercise No: 13.8
Name two safety measures commonly used in electric circuits and
(i) Fuse: it is connected in series and protects the circuit from overloading and short circuiting.
(ii) Earthling: any leakage of current in electric appliance gets transferred to ground.
An electric oven of 2 kW is operated in a domestic electric circuit (220 V)
that has a current rating of 5 A. What result do you expect? Explain.
Power of the oven (P) = 2 kW = 2000 W
Potential Difference (V) = 220 V
we have P = VI
Here, the current drawn by the electric oven is 9.09 A, which exceeds the safe limit of the circuit that is 5A. Therefore electric fuse will melt and break the circuit.
What precaution should be taken to avoid the overloading of domestic
(i) We can use fuse for protection from overloading.
(ii) Use of faulty appliances should be prohibited.
(iii) Use of too many appliance in same socket should be prohibited.
(iv) Using of appliances within safe limit.
Exercise Chapter 13
Which of the following correctly describes the magnetic field near a long
(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
(e) The field consists of concentric circles centred on the wire
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
(c) Producing induced current in a coil due to relative motion between a magnet and the coil
The device used for producing electric current is called a
The essential difference between an AC generator and a DC generator is
(a) AC generator has an electromagnet while a DC generator has
(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 commentator.
(d) AC generator has slip rings while the DC generator has a commentator.
At the time of short circuit, the current in the circuit:
(a) reduces substantially
(b) does not change
(c) increases heavily
(d) vary continuously.
(c) Increases heavily
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
(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
List three sources of magnetic fields.
(i) Current-carrying conductor.
(ii) Permanent magnet.
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
Current in each circular loop has the same direction inside a solenoid. When current is passed through the solenoid, magnetic field gets combined effectively to produce strong magnetic field. Hence, solenoid behaves like a magnet.
Magnetic field is almost uniform and parallel to axis inside a solenoid.
If we bring North Pole of bar magnet towards one end of solenoid, if it attracts then solenoid has south polarity and other end has north polarity. If it repels, then solenoid has north polarity and other end has south polarity.
When is the force experienced by a current-carrying conductor placed in a
magnetic field largest
When the directions of electric and magnetic fields become perpendicular to each other then the force experienced by a current-carrying conductor placed in magnetic field is largest.
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?
We use Fleming’s left hand rule for direction of magnetic field. Since electron is moving from back wall to front wall then direction of electric field must be opposite.
Now the direction of force is towards right, we can conclude that the magnetic field inside the chamber is in downward direction.
Draw a labeled diagram of an electric motor. Explain its principle and
working. What is the function of a split ring in an electric motor?
An electric motor is a rotating device that converts electrical energy to mechanical energy.
Principle of an electric motor is that when a rectangular coil is placed in magnetic field and a current is passed through it, then a force acts on the coil which rotates it continuously.
(i) When battery is switched on, current flows through coil AB from A to B, and magnetic field is from North to South. By Fleming’s left-hand rule, a downward force is applied on AB.
(ii) Similarly an upward force is applied on CD moving the coil up.
(iii) When coil becomes parallel to magnetic field, the brushed X and Y touch the gap between the rings, breaking the circuit.
(iv) Due to inertia, ring keeps moving so that the opposite end of the ring is now connected the positive end of wire.
(v) Split ring P is connected to CD and ring Q connected to AB which reverses the direction of current in the circuit.
(vi) Now current in CD becomes reversed i.e from D to C. So, coil keeps rotating.
Function of split ring –
It is used to reverse the flow of current and make coil and axle rotate in same direction.
Name some devices in which electric motors are used?
Washing machines, water pumps, electric fans, mixers , grinders.
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?
When a coil of insulated copper wire is connected to galvanometer
(i) When a bar magnet is pushed into the coil, magnetic field around it will change and hence, some current induced in coil. Galvanometer will show some deflection.
(ii) When a bar magnet is withdrawn from inside the coil, it will vary the magnetic field around the coil and some current is induced in the coil and hence, galvanometer shows deflection but in opposite direction.
(iii) When a bar magnet is held stationary inside the coil, no magnetic field changes and no current is induced, galvanometer will not show deflection.
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
Current in the coil A will generate a magnetic field around it. As B is placed near the coil A , it will experience a magnetic field.
When current in A is varied , magnetic field also changes accordingly and hence, magnetic field around B also changes which will induce a electric current in coil B , this is called electromagnetic induction.
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) Right hand thumb rule
(ii) Fleming’s left hand rule
(iii) Fleming’s right hand rule
Explain the underlying principle and working of an electric generator by
drawing a labelled diagram. What is the function of brushes?
Principle of electric generator is based on Fleming’s left-hand rule. When a coil is forced to
rotate in magnetic field then an electric current is induced.
(i) Let’s assume coil is rotated clockwise, side AB moves up and CD moves down. By Fleming’s left hand rule on side AB, force is upwards, magnetic field is left to right, so current flows from A to B. and on side CD current flows from C to D.
(ii) Hence, current flows into the brush B2 , moves along galvanometer and enters b1.
(iii) After half rotation, side CD comes on left side and AB on right side.
(iv) Now when CD comes left, by Fleming’s left-hand rule force is downwards and magnetic field is left to right. So, current flows from D to C.
(v) Hence, in our circuit DCBA the current moves in opposite direction.
(vi) Thus after every half rotation, direction of current changes and hence, alternating current is produced. Function of brushes is that the brushes conduct current between stationary wires and moving parts of electric generator.
When does an electric short circuit occur?
Short circuit occurs if the insulation used in wire is damaged so that live wire and neutral wire comes in direct contact with each other and it causes overloading. Due to overloading, current increases rapidly and short circuit occurs.
What is the function of an earth wire? Why is it necessary to earth metallic
The Earth wire transfers the leaking current from electrical appliance to the ground. It is necessary to earth metallic appliance as it saves user from severe shock by transferring current to ground.