Shivendra Sarairasi

 

KNOWLEDGE ACADEMY AYODHYA

CLASS 10 – SCIENCE

CHAPTER: MAGNETIC EFFECTS OF ELECTRIC CURRENT

1. Introduction

Electricity and magnetism are closely related to each other. When an electric current flows through a conductor, it produces a magnetic field around it. This phenomenon is called the magnetic effect of electric current.

Example: A compass needle placed near a current-carrying wire gets deflected.

2. Magnetic Field

The region around a magnet where its magnetic force can be experienced is called a magnetic field.

SI unit: Tesla (T)

A magnetic field is represented by the symbol B.

3. Magnetic Field Lines

Magnetic field lines are imaginary lines used to represent the magnetic field around a magnet.

Properties of Magnetic Field Lines

1. Outside a bar magnet, magnetic field lines emerge from the North Pole and enter the South Pole.
2. Inside the magnet, they travel from the South Pole to the North Pole.
3. Magnetic field lines form closed curves.
4. No two magnetic field lines intersect each other.
5. The closer the field lines, the stronger the magnetic field.
6. The direction of the magnetic field at any point is given by the tangent to the field line at that point.

4. Magnetic Field Around a Straight Current-Carrying Conductor

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

Factors Affecting the Magnetic Field

1. The magnetic field strength increases when the current increases.
2. The magnetic field strength decreases as the distance from the conductor increases.
3. Reversing the direction of current reverses the direction of the magnetic field.

5. Right-Hand Thumb Rule

The right-hand thumb rule determines the direction of the magnetic field around a straight current-carrying conductor.

Statement: If we hold a current-carrying straight conductor in our right hand so that the thumb points in the direction of current, the curled fingers indicate the direction of the magnetic field.

Application: Finding the direction of the magnetic field around a straight wire.

6. Magnetic Field Due to a Circular Loop

When an electric current passes through a circular loop of wire, a magnetic field is produced around it.

The magnetic field near the centre of the loop is almost perpendicular to the plane of the loop.

Factors Affecting Magnetic Field Strength

1. Increasing the current increases the magnetic field strength.
2. Increasing the number of turns increases the magnetic field strength.
3. The magnetic field also depends on the size and geometry of the loop.

7. Magnetic Field Due to a Solenoid

A solenoid is a long cylindrical coil consisting of many circular turns of insulated copper wire.

When electric current passes through a solenoid, it produces a magnetic field similar to that of a bar magnet.

Properties of a Solenoid

1. One end behaves like a North Pole and the other like a South Pole.
2. The magnetic field inside a long solenoid is strong and nearly uniform.
3. The magnetic field becomes stronger when the current increases.
4. Increasing the number of turns per unit length increases the magnetic field strength.
5. Inserting a soft iron core inside the solenoid can produce a strong electromagnet.

8. Electromagnet

An electromagnet is a temporary magnet produced by passing electric current through a coil, usually wound around a soft iron core.

Uses of Electromagnets

1. Electric bells
2. Electromagnetic cranes
3. Electric relays
4. Electric motors
5. Magnetic separation of iron materials

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

When a current-carrying conductor is placed in a magnetic field, it experiences a force if the current and magnetic field are not parallel.

The direction of the force depends on the direction of the electric current and the magnetic field.

The force is greatest when the current and magnetic field are perpendicular. It is zero when they are parallel or antiparallel.

Fleming's Left-Hand Rule

Stretch the thumb, forefinger and middle finger of your left hand so that they are mutually perpendicular.

• Forefinger: Direction of magnetic field
• Middle finger: Direction of current
• Thumb: Direction of force or motion

Application: Electric motors.

10. Electric Motor

An electric motor is a device that converts electrical energy into mechanical energy.

Principle

A current-carrying coil placed in a magnetic field experiences a force that can produce rotation.

Main Parts

1. Armature coil
2. Permanent magnet
3. Split-ring commutator
4. Carbon brushes
5. Battery or DC power supply

Working

1. A rectangular coil is placed between the poles of a magnet.
2. When current flows through the coil, its two sides experience forces in opposite directions.
3. These forces produce a turning effect, causing the coil to rotate.
4. After every half rotation, the split-ring commutator reverses the direction of current in the coil.
5. The coil continues rotating in the same direction.

Uses

• Electric fans
• Mixers
• Washing machines
• Water pumps
• Electric toys

11. Electromagnetic Induction

The phenomenon of producing an induced current in a conductor by changing the magnetic field linked with it is called electromagnetic induction.

It was discovered by Michael Faraday.

Ways to Produce Induced Current

1. Move a magnet towards or away from a coil.
2. Move a coil towards or away from a magnet.
3. Change the magnetic field linked with the coil.

The induced current can be detected using a galvanometer.

12. Fleming's Right-Hand Rule

This rule determines the direction of induced current when a conductor moves in a magnetic field.

Stretch the thumb, forefinger and middle finger of your right hand so that they are mutually perpendicular.

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

Application: Electric generators.

13. Electric Generator

An electric generator is a device that converts mechanical energy into electrical energy.

Principle

It works on the principle of electromagnetic induction.

Main Parts of an AC Generator

1. Armature coil
2. Strong magnet
3. Slip rings
4. Carbon brushes
5. Axle

Working

1. A coil is rotated mechanically between the poles of a magnet.
2. As the coil rotates, the magnetic field linked with it changes.
3. This induces an electric current in the coil.
4. The direction of current reverses after every half rotation.
5. Slip rings and carbon brushes transfer the current to the external circuit.

An AC generator produces alternating current.

14. Alternating Current and Direct Current

Alternating Current (AC)

An electric current that changes its direction periodically is called alternating current.

Example: The electricity supplied to homes in India is AC, with a frequency of approximately 50 Hz.

Direct Current (DC)

An electric current that flows in one direction is called direct current.

Example: Current supplied by a battery.

Difference Between AC and DC

Alternating Current (AC)	Direct Current (DC)
Changes direction periodically.	Flows in one direction.
Has a frequency.	Steady DC has zero frequency.
Used in domestic electricity supply.	Produced by cells and batteries.

15. Domestic Electric Circuits

Electrical appliances in homes are generally connected in parallel.

Advantages of Parallel Connection

1. Each appliance receives the same supply voltage.
2. Each appliance can be operated independently.
3. If one appliance stops working, the others can continue working.

Three Wires in Domestic Circuits

1. Live Wire: Carries current from the supply.

2. Neutral Wire: Provides the return path for current.

3. Earth Wire: Provides a low-resistance path for leakage current to the ground, helping protect users from electric shock.

16. Electric Fuse

An electric fuse is a safety device that protects an electrical circuit from excessive current.

It contains a wire with a relatively low melting point. When excessive current flows, the wire heats up, melts and breaks the circuit.

A fuse is connected in series with the live wire.

17. Short Circuit

A short circuit occurs when the live and neutral wires come into direct contact, creating a path of very low resistance.

This can cause a sudden increase in current and may lead to overheating or fire.

18. Overloading

Overloading occurs when the current flowing through a circuit exceeds its safe limit.

Causes of Overloading

1. Connecting too many appliances to one socket.
2. Using several high-power appliances on the same circuit.
3. A fault in the electrical circuit.

Prevention

Use properly rated protective devices and avoid connecting too many high-power appliances to one socket.

19. Difference Between Electric Motor and Electric Generator

Electric Motor	Electric Generator
Converts electrical energy into mechanical energy.	Converts mechanical energy into electrical energy.
Works on the force experienced by a current-carrying conductor in a magnetic field.	Works on electromagnetic induction.
Uses a current-carrying coil in a magnetic field.	Uses relative motion between a coil and a magnetic field.
Used in fans and mixers.	Used to generate electricity.

20. Important Definitions

1. Magnetic Field: The region around a magnet where its magnetic force can be experienced.

2. Magnetic Field Lines: Imaginary lines representing the direction and relative strength of a magnetic field.

3. Solenoid: A cylindrical coil consisting of many turns of insulated wire.

4. Electromagnet: A magnet produced by electric current, usually using a soft iron core.

5. Electric Motor: A device that converts electrical energy into mechanical energy.

6. Electromagnetic Induction: The production of induced current due to a change in the magnetic field linked with a conductor.

7. Electric Generator: A device that converts mechanical energy into electrical energy.

8. Short Circuit: A condition in which current flows through an unintended path of very low resistance.

9. Overloading: A condition in which the current drawn by a circuit exceeds its safe limit.

IMPORTANT BOARD EXAM QUESTIONS

Very Short Answer Questions

1. What is the magnetic effect of electric current?
2. What is the SI unit of magnetic field?
3. Who discovered electromagnetic induction?
4. State the right-hand thumb rule.
5. What is a solenoid?
6. What is an electromagnet?
7. State Fleming's left-hand rule.
8. What is the principle of an electric motor?
9. What is electromagnetic induction?
10. State Fleming's right-hand rule.

Short Answer Questions

11. Write any four properties of magnetic field lines.
12. Describe the magnetic field around a straight current-carrying conductor.
13. How can the strength of the magnetic field of a solenoid be increased?
14. Explain the working principle of an electric motor.
15. Explain electromagnetic induction with an example.
16. Differentiate between AC and DC.
17. Why are household appliances connected in parallel?
18. Explain the functions of the live, neutral and earth wires.
19. What are short circuiting and overloading?
20. Differentiate between an electric motor and an electric generator.

Long Answer Questions

21. Explain the magnetic field due to a current-carrying solenoid with a labelled diagram.

22. Draw a labelled diagram of an electric motor and explain its working.

23. Draw a labelled diagram of an AC generator and explain its principle and working.

24. Explain Fleming's left-hand rule and right-hand rule with their applications.

25. Explain the arrangement and safety features of a domestic electric circuit.

QUICK REVISION

Topic	Key Point
Magnetic field	Measured in tesla
Right-hand thumb rule	Direction of magnetic field
Solenoid	Produces a magnetic field similar to a bar magnet
Fleming's left-hand rule	Direction of force
Electric motor	Electrical energy → Mechanical energy
Electromagnetic induction	Induced current due to changing magnetic field
Fleming's right-hand rule	Direction of induced current
Electric generator	Mechanical energy → Electrical energy
AC	Current changes direction periodically
DC	Current flows in one direction
Electric fuse	Protects against excessive current
Earth wire	Provides a safety path for leakage current

Exam Preparation Tip: Practise the labelled diagrams of a straight current-carrying conductor, a solenoid, an electric motor and an AC generator. Learn both Fleming's rules carefully and prepare the differences between a motor and a generator.