# Ch 12: Magnetic Effects of Electric Current (NCERT Solutions)

NCERT Solutions for Class 10 Science Ch 12: Magnetic Effects of Electric Current, is given below.

You will get solutions for;

• In-text questions as well as,
• Exercises questions.

So let’s dive into it!

## In-text Questions Set-1

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

Solution:
The compass needle is a small magnet. When you bring it near a bar magnet, the magnetic fields of both the compass needle and the bar magnet interact. This interaction causes the compass needle to move.

## In-text Questions Set-2

1) Draw magnetic field lines around a bar magnet.

Solution:
Magnetic field lines around a bar magnet are shown below:

2) List the properties of magnetic field lines.

Solution:
Properties of Magnetic Field Lines:

– Outside a magnet, the field lines go from the north (N) pole to the south (S) pole. Inside the magnet, they go from the south (S) pole to the north (N) pole.
– Magnetic field lines form closed loops.
– Magnetic field lines never cross each other.
– The strength of the magnetic field is shown by how close the lines are to each other.

3) Why don’t two magnetic field lines intersect each other?

Solution:
Magnetic field lines never intersect. If they did, it would imply that the magnetic field has two directions at that point, which isn’t possible.

## In-text Questions Set-3

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.

Solution:

According to the right-hand rule, inside the loop, the magnetic field lines point perpendicular to the paper and go inward. Outside the loop, the magnetic field lines point outward from the paper.

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

Solution:

The uniform magnetic field is shown with evenly spaced, parallel lines.

3) Choose the correct option:
The magnetic field inside a long straight solenoid-carrying current
(a) Is zero.
(b) Decrease as we move towards its end.
(c) Increase as we move towards its end.
(d) Is the same at all points.

Solution:
(d) Is the same at all points.

## In-text Questions Set-4

1) Which of the following property of a proton can change while it moves freely in a magnetic field?
(a) mass
(b) speed
(c) velocity
(d) momentum

Solution:
(c) and (d)
When a proton moves into a magnetic field, it feels a magnetic force that makes it follow a circular path. This force changes the proton’s velocity and momentum.

2) In Activity 12.7, 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?

Solution:
When a conductor carrying current is placed in a magnetic field, it feels a force. This force gets stronger if the current is higher, the conductor is longer, or the magnetic field is stronger.

Therefore, the force on rod AB and its movement will increase if:
1. The current in rod AB is increased
2. A stronger magnet is used
3. The length of rod AB is increased

3) A positively-charged particle (alpha-particle) projected towards the 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

Solution:
(d) upward

## In-text Questions Set-5

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

Solution:
Safety measures in electric circuits are:

Fuse:
Every circuit should have a fuse. A fuse stops too much current from flowing through by melting when the current gets too high. This protects the devices connected to the circuit.

Earthing:
Earthing helps protect people from electric shocks. If there’s a current leak in an appliance, earthing directs the electricity safely to the ground, preventing electric shocks to users.

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.

Solution:
To find the current drawn by the electric oven, use the formula:
P = V × I
I = P/V

Substituting the values, we get,
I = 2000 W/220 V = 9.09 A

The oven draws 9.09 A, which is higher than the safe limit for the circuit. This overload causes the fuse to blow and break the circuit.

3) What precaution should be taken to avoid the overloading of domestic electric circuits?

Solution:

– Avoid connecting too many devices to one socket.
– Don’t use too many appliances at the same time.
– Don’t connect faulty appliances to the circuit.

## Exercise Questions

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 centered on the wire

Solution:
(d) The field consists of concentric circles centered on the wire

2) At the time of short circuit, the current in the circuit:
(a) reduce substantially
(b) does not change
(c) increase heavily
(d) vary continuously

Solution:
(c) increase heavily

3) State whether the following statements are true or false.
(a) The field at the center 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.

Solution:
(a) True
A long circular coil is called a solenoid. Inside a solenoid, the magnetic field lines run parallel and straight.

(b) False
Live wires have a red insulation cover, while the earth wire is covered in green insulation.

4) List two methods of producing magnetic fields.

Solution:
Here are some ways to create magnetic fields:

– Using a Permanent Magnet: You can see the magnetic field by placing a magnet under a sheet of white paper and spreading iron filings on top. The filings will arrange themselves in the shape of the magnetic field.

– Current Carrying Wire: A straight wire carrying an electric current also creates a magnetic field around it.

– Coils and Loops: Different types of conductors, like solenoids (coiled wires) and circular loops, can also produce and show magnetic fields.

5) When is the force experienced by a current–carrying conductor placed in a magnetic field largest?

Solution:
The force is largest when the current flows at a right angle to the magnetic field.

6) 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?

Solution:
To find the direction of the magnetic field, use Fleming’s Left-Hand Rule. This rule tells us that the magnetic field direction is at right angles to both the current direction and the deflection direction (either up or down).

In this case, the current flows from the front wall to the back wall because electrons move from the back wall to the front wall. Since the magnetic force is directed to the right, Fleming’s Left-Hand Rule shows that the magnetic field inside the chamber points downward.

7) 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.

Solution:
(i) To find the direction of the magnetic field around a straight current-carrying conductor, use Maxwell’s right-hand thumb rule.

(ii) To determine the force on a straight conductor carrying current in a magnetic field perpendicular to it, use Fleming’s left-hand rule.

(iii) To find the direction of the current induced in a rotating coil within a magnetic field, use Fleming’s right-hand rule.

8) When does an electric short circuit occur?

Solution:
Here are two common situations that can cause a short circuit:

– If too many appliances are plugged into one socket, or if high-power appliances are connected to a light circuit, the circuit’s resistance drops. This causes a high current to flow through the circuit, leading to a short circuit.

– If the insulation on live wires wears off and they touch each other, the current flow suddenly increases, causing a short circuit.

9) What is the function of an earth wire? Why is it necessary to earth metallic appliances?

Solution:
Electric appliances with metallic bodies are connected to the ground using an earth wire. This earth wire safely directs any stray electrical currents away from the appliance and into the ground.

By doing so, it prevents users from receiving electric shocks. That’s why grounding metallic appliances is essential for safety.