Magnetic Effects of Electric Current

1. Introduction

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. This concept forms the foundation of many electrical devices such as electric motors, generators, electric bells, fans, and transformers.

The magnetic effect of electric current was discovered by Hans Christian Oersted in 1820. He observed that a compass needle placed near a current-carrying wire gets deflected, proving that electric current produces a magnetic field.

2. Magnetic Field

Definition

The region around a magnet or a current-carrying conductor in which magnetic force can be experienced is called a magnetic field.

Properties of Magnetic Field Lines

Magnetic field lines are imaginary lines used to represent a magnetic field.

They emerge from the North Pole and enter the South Pole of a magnet.
Inside the magnet, they move from South Pole to North Pole, forming closed loops.
No two magnetic field lines intersect each other.
The closeness of field lines indicates the strength of the magnetic field.

3. Magnetic Field Due to a Current-Carrying Straight Conductor

When electric current flows through a straight conductor, concentric circular magnetic field lines are formed around it.

Right-Hand Thumb Rule

Hold the conductor in your right hand.
The thumb points in the direction of current.
The curled fingers give the direction of the magnetic field lines.

Factors Affecting Magnetic Field Strength

Magnitude of current: More current produces a stronger magnetic field.
Distance from the conductor: Magnetic field decreases with increase in distance.

4. Magnetic Field Due to a Circular Current-Carrying Loop

A circular loop carrying current produces a magnetic field similar to that of a bar magnet.

Magnetic field at the center of the loop is maximum.
Increasing the number of turns increases the strength of the magnetic field.
Direction of magnetic field is given by the Right-Hand Thumb Rule.

5. Solenoid

Definition

A solenoid is a long cylindrical coil consisting of a large number of closely spaced turns of insulated copper wire.

Magnetic Field of a Solenoid

The magnetic field inside a solenoid is strong and uniform.
The magnetic field outside is weak.
One end of the solenoid behaves like a North Pole and the other like a South Pole.

Electromagnet

When a soft iron core is placed inside a solenoid, it becomes a strong electromagnet.

Advantages of Electromagnets

Magnetism can be switched ON and OFF.
Strength can be controlled by changing current.

Uses of Electromagnets

Electric bells
Cranes for lifting iron objects
Relays and circuit breakers

6. Force on a Current-Carrying Conductor in a Magnetic Field

A current-carrying conductor placed in a magnetic field experiences a force. The force depends on:

Strength of magnetic field
Amount of current
Length of conductor

Fleming’s Left-Hand Rule

This rule helps to determine the direction of force.

Thumb: Direction of force (motion of conductor)
Forefinger: Direction of magnetic field
Middle finger: Direction of current

7. Electric Motor

Principle

An electric motor works on the principle that a current-carrying conductor placed in a magnetic field experiences a force.

Construction

Rectangular coil
Strong magnetic field
Split-ring commutator
Carbon brushes
DC source

Working

When current flows through the coil, forces act on opposite sides of the coil in opposite directions, causing the coil to rotate continuously.

Uses of Electric Motor

Electric fans
Washing machines
Mixers and grinders

8. Electromagnetic Induction

Definition

The production of electric current in a conductor due to a change in magnetic field is called electromagnetic induction.

Discovery

Discovered by Michael Faraday.

9. Fleming’s Right-Hand Rule

This rule determines the direction of induced current.

Thumb: Direction of motion of conductor
Forefinger: Direction of magnetic field
Middle finger: Direction of induced current

10. Electric Generator

Principle

An electric generator works on the principle of electromagnetic induction.

Types

AC Generator
DC Generator

Uses

Production of electricity in power stations

11. Difference Between AC and DC

Alternating Current (AC)	Direct Current (DC)
Direction changes periodically	Direction remains constant
Used in homes	Used in batteries

12. Domestic Electric Circuits – Safety Devices

Fuse

A fuse protects electrical appliances by breaking the circuit when excess current flows.

Earthing

Earthing provides a low-resistance path to prevent electric shock.

Very Short Answer (1 Mark)

What is the magnetic effect of electric current?
Answer: The phenomenon of production of a magnetic field around a current-carrying conductor is called the magnetic effect of electric current.
Who discovered the magnetic effect of electric current?
Answer: Hans Christian Oersted.
Name the rule used to find the direction of magnetic field around a straight conductor.
Answer: Right-Hand Thumb Rule.
Which device converts electrical energy into mechanical energy?
Answer: Electric motor.
Which principle is used in an electric generator?
Answer: Electromagnetic induction.

Short Answer (2–3 Marks)

State any two properties of magnetic field lines.
Answer:
(a) Magnetic field lines form closed loops.
(b) No two magnetic field lines intersect each other.
What is a solenoid? Write one use.
Answer: A solenoid is a long cylindrical coil of insulated wire having many turns. It is used to make electromagnets.
State Fleming’s Left-Hand Rule.
Answer: When the thumb, forefinger and middle finger of the left hand are stretched mutually perpendicular to each other, the forefinger shows the direction of magnetic field, the middle finger shows the direction of current and the thumb shows the direction of force.
Why are electromagnets preferred over permanent magnets?
Answer: Electromagnets are preferred because their magnetism can be controlled and switched ON or OFF.

Long Answer

Explain the construction and working of an electric motor.
Answer:
An electric motor works on the principle that a current-carrying conductor placed in a magnetic field experiences a force. It consists of a rectangular coil placed between the poles of a magnet, split-ring commutator, carbon brushes and a DC source. When current flows through the coil, opposite forces act on its sides, causing the coil to rotate continuously.
Explain electromagnetic induction.
Answer:
Electromagnetic induction is the phenomenon of production of electric current in a conductor due to change in magnetic field around it. It was discovered by Michael Faraday and is the basic principle of electric generators.

PART 2: NUMERICAL PROBLEMS (Solved)

A straight conductor carries a current of 2 A. What happens to the magnetic field if the current is increased to 4 A?
Solution: Magnetic field strength is directly proportional to current. When current is doubled, the magnetic field strength also doubles.
Name the factors on which force acting on a current-carrying conductor depends.
Answer:
(a) Strength of magnetic field
(b) Magnitude of current
(c) Length of conductor
A conductor is placed perpendicular to a magnetic field. What will be the effect on force if current is increased?
Answer: The force acting on the conductor will increase.

PART 3: MULTIPLE CHOICE QUESTIONS (MCQs)

The magnetic effect of electric current was discovered by:
(a) Faraday (b) Fleming (c) Oersted (d) Maxwell
Answer: (c) Oersted
Direction of magnetic field around a current-carrying conductor is given by:
(a) Fleming’s Left-Hand Rule
(b) Fleming’s Right-Hand Rule
(c) Right-Hand Thumb Rule
(d) Maxwell’s Rule
Answer: (c) Right-Hand Thumb Rule
Which device works on the principle of electromagnetic induction?
(a) Electric motor
(b) Electric generator
(c) Electric bell
(d) Transformer
Answer: (b) Electric generator
In Fleming’s Left-Hand Rule, the thumb represents:
(a) Magnetic field
(b) Current
(c) Force
(d) Induced current
Answer: (c) Force
Which current is supplied to homes?
(a) DC
(b) AC
(c) Both
(d) None
Answer: (b) AC

Monday, January 05, 2026