Class 10

Magnetic Effects of Electric Current (NCERT Exercise Solutions)

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.

Explanation:
When current flows through a straight conductor, the magnetic field lines form concentric circles around the wire. The direction of field lines is given by the Right-Hand Thumb Rule.

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.

Explanation:
In a short circuit, resistance becomes very low, so a large current flows through the circuit. This sudden increase can cause damage to appliances.

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.
✅ True

(b) A wire with green insulation is usually the live wire of an electric supply.
✅ False

Explanation:
Green wire is earth wire, not live wire.
The live wire is red or brown, and the neutral wire is black or blue.

Q4.

List two methods of producing magnetic fields.

✅ Answer:

By passing electric current through a straight conductor.
By passing electric current through a circular coil or solenoid.

Q5.

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

✅ Answer:
The force is maximum when the conductor is perpendicular to the magnetic field,
and zero when it is parallel to the magnetic field.

Q6.

Imagine you are sitting in a chamber with your back to one wall.
An electron beam moves horizontally from back wall to front wall and is deflected by a strong magnetic field to your right side.
What is the direction of the magnetic field?

✅ Answer:
Use the Fleming’s Left-Hand Rule.

Motion of electron beam → from back to front.
Force (deflection) → towards right.
Because electrons move opposite to conventional current,
the magnetic field will be in the downward direction.

Q7.

State the rule to determine the direction of:

(i) magnetic field produced around a straight current-carrying conductor,
(ii) force experienced by a current-carrying conductor in a magnetic field, and
(iii) current induced in a coil due to rotation in a magnetic field.

✅ Answer:
(i) Right-Hand Thumb Rule:
Hold the wire in your right hand with thumb pointing in the direction of current; the curl of fingers gives the direction of magnetic field.

(ii) Fleming’s Left-Hand Rule:
Stretch the thumb, forefinger, and middle finger of the left hand at right angles.

Forefinger → direction of magnetic field (B)
Middle finger → direction of current (I)
Thumb → direction of force (motion).

(iii) Fleming’s Right-Hand Rule:
Used for generators.
If the thumb, forefinger, and middle finger of the right hand are stretched perpendicular to each other —

Thumb → motion of conductor
Forefinger → magnetic field
Middle finger → induced current.

Q8.

When does an electric short circuit occur?

✅ Answer:
A short circuit occurs when the live wire and neutral wire come in direct contact with each other.
This reduces resistance sharply and causes a large current to flow, which can damage the circuit or cause fire.

Q9.

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

✅ Answer:
The earth wire provides a low-resistance path for electric current to flow safely into the ground in case of leakage.
It prevents electric shock and protects users from damage if the metal body of an appliance becomes live due to a fault.

Example: Refrigerator, iron, washing machine, etc., must be earthed for safety.

🔹 FAQs (for WordPress FAQ block or Schema)

Q1. What is the Magnetic Effects of Electric Current?

Answer: When an electric current flows through a conductor, it produces a magnetic field around it. This phenomenon is known as the magnetic effect of electric current.

Q2. What are the main topics covered in Chapter 12 Magnetic Effects of Electric Current?

Answer: The main topics are magnetic field and field lines, Right-Hand Thumb Rule, Fleming’s Rules, solenoid, electric motor, electric generator, and safety measures like fuses and earthing.

Q3. What is the Right-Hand Thumb Rule?

Answer: If you hold a current-carrying conductor with your right hand such that the thumb points in the direction of current, the curl of the fingers gives the direction of magnetic field lines.

Q4. What is the difference between Fleming’s Left-Hand Rule and Right-Hand Rule?

Answer:

Left-Hand Rule is used for electric motors (to find direction of motion).
Right-Hand Rule is used for electric generators (to find direction of induced current).

Q5. Why is earthing necessary for electrical appliances?

Answer: Earthing provides a safe path for leakage current to flow into the ground. It protects users from electric shocks and prevents damage to appliances.

NCERT Solution Class 10 Science Chapter 12 Magnetic Effects of Electric Current