Chapter 13. Magnetic Effects of Electric Current

Class 10 Science Chapter 13. Magnetic Effects of Electric Current Internal Questions and Answers :

Q1. Why does a compass needle get deflected when brought near a bar magnet?

Answer:  A compass needle gets deflected when brought near a bar magnet due to the magnetic field produced by the magnet. The compass needle aligns itself with the magnetic field lines, indicating the presence and direction of the magnetic field.

Example 13.1
A current through a horizontal power line flows in east to west direction. What is the direction of magnetic field at a point directly below it and at a point directly above it?

Answer : At a point directly below the horizontal power line, the direction of the magnetic field is vertically upward.

At a point directly above the horizontal power line, the direction of the magnetic field is vertically downward.

Internal Questions :

Q1. Draw magnetic field lines around a bar magnet.

Answer : We draw magnetic field lines around a bar magnet :

Q2. List the properties of magnetic lines of force.

Answer:  The properties of magnetic lines of force are:

(i)  They always form closed loops, emerging from the north pole and entering the south pole.

(ii)  They never intersect each other.

(iii) The density of lines indicates the strength of the magnetic field.

(iv)  They repel each other in a uniform field.

(v) They are directed from the north to the south pole outside the magnet.

Q3. Why don’t two magnetic lines of force intersect each other?

Answer: Two magnetic lines of force do not intersect each other because if they were to intersect, it would imply that a given point in space has two different directions of the magnetic field, which is not possible.

Internal Questions :

Q1. 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:  Inside the loop: By applying the right-hand rule, point your thumb in the direction of the current. The fingers curl in the direction of the magnetic field. For a clockwise current, the field inside the loop points downward, perpendicular to the plane of the loop.

Outside the loop: The field lines curve outward and eventually loop back into the opposite side.

Q2. The magnetic field in a given region is uniform. Draw a diagram to represent it.

Answer :

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.

Inside a long straight solenoid carrying current, the magnetic field is uniform, and its strength is the same at all points along the axis of the solenoid. This is one of the unique characteristics of a well-designed solenoid.

Example 13.2
An electron enters a magnetic field at right angles to it, as shown in Fig. 13.14. The direction of force acting on the electron will be

       Fig 13.14

(a) to the right.
(b) to the left.
(c) out of the page.
(d) into the page.

Answer : (d) into the page .

The direction of force is perpendicular to the direction of magnetic field and current as given by Fleming’s left hand rule. Again, the direction of current is taken opposite to the direction of motion of electrons. The force is therefore directed into the page .

Internal Questions :

Q1. 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 : The correct answers are:

(c) Velocity and (d) Momentum

[ A magnetic field exerts a force perpendicular to the motion of the proton, causing its direction (and thus velocity) to change.

Since momentum depends on velocity (), it also changes.

The mass and speed of the proton remain unchanged because the magnetic field does no work.]

Q2. 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 : The displacement of rod AB will be affected as follows:
(i) Increasing current in rod AB: The force on the rod increases, resulting in greater displacement.
(ii) Using a stronger horse-shoe magnet: A stronger magnetic field increases the force, causing more displacement.
(iii) Increasing the length of rod AB: A longer rod increases the force, leading to greater displacement.

Q3. 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

Answer :  (d) upward

When a positively-charged particle (such as an alpha-particle) is projected towards the west and is deflected towards the north by a magnetic field, it implies that the magnetic field is acting perpendicular to both the initial velocity (west) and the direction of deflection (north). According to the right-hand rule for positive charges, the magnetic field points upward in this scenario.

Internal Questions :

Q1. State Fleming’s left-hand rule.

Answer :  Fleming's left-hand rule states: Stretch the thumb, forefinger, and middle finger of your left hand mutually perpendicular to each other. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of current, then the thumb will point in the direction of motion or the force acting on the conductor.

Internal Questions :

Q1. Name two safety measures commonly used in electric circuits and appliances.

Answer: Two safety measures commonly used in electric circuits and appliances are:

(i) Fuse: Protects circuits and appliances from overloading or short circuits by breaking the circuit when the current exceeds a safe limit.

(ii) Earthing: Provides a safe path for excess current to flow into the ground, preventing electric shocks.

Q2. 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: The power of the electric oven is  and the voltage of the circuit is

We have, 

The current required by the oven (9.09 A) exceeds the circuit's current rating (5 A). As a result, the circuit will likely be overloaded, causing the fuse to blow or a circuit breaker to trip, cutting off the electricity supply to prevent damage or fire.

Q3. What precaution should be taken to avoid the overloading of domestic electric circuits ?

Answer: To avoid overloading of domestic electric circuits, the following precautions should be taken:

(i) Avoid connecting too many high-power appliances to a single circuit.

(ii) Use appropriate fuses or circuit breakers to disconnect the circuit during excessive current flow.

(iii) Ensure proper wiring and use wires of suitable thickness to handle the current.

(iv) Avoid using damaged or old appliances that may cause short circuits.

(v) Distribute the load evenly across multiple circuits.

Class 10 Science Chapter 13 Magnetic Effects of Electic Current Exercise Questions and Answers :

Q1. 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.

[ When a current flows through a long straight wire, the magnetic field around the wire forms concentric circles. The direction of the magnetic field lines can be determined using the right-hand rule: if you point your thumb in the direction of the current, the curling of your fingers shows the direction of the magnetic field lines around the wire.]

Q2. At the time of short circuit, the current in the circuit
(a) reduces substantially.
(b) does not change.
(c) increases heavily.
(d) vary continuously.

Answer :  (c) increases heavily.

[ During a short circuit, the low-resistance path causes a rapid surge in current, as there is little impedance to limit the flow. This can be dangerous and damaging.]

Q3. State whether the following statements are true or false.
(a) The field at the centre of a long circular coil carrying current will be parallel straight lines.
(b) A wire with a green insulation is usually the live wire of an electric supply.

Answer : (a) True: The magnetic field at the center of a long circular coil carrying current consists of parallel straight lines, indicating a uniform field.

(b) False: A wire with green insulation is typically the earth wire, not the live wire, in an electric supply.

Q4. List two methods of producing magnetic fields.

Answer: Two methods of producing magnetic fields are:

(i) Using a current-carrying conductor: A magnetic field is generated around a wire when an electric current flows through it.

(ii) Using a permanent magnet: A magnetic field is produced naturally around permanent magnets due to the alignment of magnetic domains.

Q5. 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 in a magnetic field is largest when the conductor is placed perpendicular to the magnetic field.
Q6. 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: The direction of the magnetic field is downward, towards the floor. Using Fleming’s left-hand rule, the electron beam's motion (opposite to current) is forward, the force is to the right, and the magnetic field points downward.
Q7. 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) Right-hand thumb rule: This rule helps determine the direction of the magnetic field around a current-carrying conductor because the magnetic field forms concentric circles around the conductor, and the direction depends on the current's flow.

(ii) Fleming’s left-hand rule: This rule identifies the direction of force because the magnetic field and current interact, generating a force perpendicular to both, as described by the motor effect.

(iii) Fleming’s right-hand rule: This rule determines the induced current's direction because the relative motion between the magnetic field and the conductor produces an electromotive force, as explained by electromagnetic induction.

Q8. When does an electric short circuit occur?

Answer: An electric short circuit occurs when the live wire and neutral wire come into direct contact due to damaged insulation or a fault in an appliance. This causes an abrupt increase in current, which can damage the circuit and appliances. A fuse prevents such damage by stopping the flow of excessively high current.

Q9. What is the function of an earth wire? Why is it necessary to earth metallic appliances ?

Answer: The function of an earth wire is to provide a safe path for leakage current to flow into the ground, preventing electric shocks.

It is necessary to earth metallic appliances because if the live wire accidentally touches the metallic body, the current flows through the earth wire instead of the user, protecting against potential electric shocks and ensuring safety.

Q10. 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: A solenoid behaves like a magnet because it generates a magnetic field similar to a bar magnet when an electric current flows through it. The magnetic field inside the solenoid is uniform and in the form of parallel straight lines, indicating a constant magnetic field.

Yes, you can determine the north and south poles of a current-carrying solenoid using a bar magnet. If you bring a bar magnet near one end of the solenoid, the end that attracts the south pole of the bar magnet will be the north pole of the solenoid, and the end that attracts the north pole of the bar magnet will be the south pole of the solenoid. The magnetic field pattern of the solenoid is similar to that of a bar magnet.