Chapter 13: Magnetic Effects of Electric Current (Class 10, NCERT Science)

By Kishore Boruah, Teacher

This chapter discusses the magnetic effects produced by electric currents, the working of electrical devices, and the applications of electromagnetism.

Artistic representation of magnetic fields 

1. Magnetic Field and Its Representation

Magnetic Field: The region around a magnet where magnetic force can be detected. It is represented by field lines.

Properties of Magnetic Field Lines:

i) They originate from the north pole and end at the south pole.

ii) They never intersect.

iii) Closer lines indicate a stronger magnetic field.

Magnetic Field Due to a Current-Carrying Conductor:

A current-carrying conductor generates a magnetic field around it.

The direction of the magnetic field can be determined using the Right-Hand Thumb Rule:

Point the thumb of the right hand in the direction of current; the curl of the fingers gives the direction of the magnetic field.

Magnetic fields and field lines 

2. Magnetic Field Due to Current Through Different Conductors

Straight Conductor: 

✓ Produces concentric circular magnetic field lines.

The right hand thumb rule :

✓ The right hand thumb rule is a way to find the direction of a magnetic field or the direction of an electric current in a wire

Right hand thumb rule

Circular Loop:

✓ The magnetic field is stronger at the center of the loop.

✓ Increasing the current or number of loops increases the field strength.

Solenoid:

✓ A coil of wire that produces a uniform magnetic field inside it.

✓ Acts like a bar magnet with north and south poles.

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

A current-carrying conductor experiences a force in a magnetic field.

✓ The Fleming’s Left-Hand Rule helps determine the direction of force:

Stretch your thumb, forefinger, and middle finger of your left hand perpendicular to each other.

Forefinger: Magnetic field direction.

Middle finger: Current direction.

Thumb: Direction of the force.

4. Electric Motor

Converts electrical energy into mechanical energy.

✓ Working Principle:

A current-carrying conductor in a magnetic field experiences a force, causing it to rotate.

✓ Components:

Armature, commutator, brushes, and magnets.

✓ Applications: Used in fans, mixers, and industrial machines.

5. Electromagnetic Induction

The process of generating an electric current in a conductor by changing the magnetic field around it.

✓ Faraday’s Experiment:

Moving a magnet near a coil or vice versa induces a current in the coil.

✓ Fleming’s Right-Hand Rule:

Stretch your thumb, forefinger, and middle finger of your right hand perpendicular to each other:

Forefinger: Direction of the magnetic field.

Thumb: Motion of the conductor.

Middle finger: Direction of induced current.

6. Electric Generator

Converts mechanical energy into electrical energy.

Working Principle:

Based on electromagnetic induction.

Types:

AC Generator: Produces alternating current.

DC Generator: Produces direct current.

7. Domestic Electric Circuits

Key Concepts:

Use of a fuse to prevent overloading and short circuits.Appliances connected in parallel for independent operation. Importance of earthing to prevent electric shocks.

This chapter explains key concepts like magnetic fields, their effects, and practical applications in daily life, emphasizing the importance of electromagnetism in modern technology.

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Chapter 13: Magnetic Effects of Electric Current – Important Questions and Answers

1. What is a magnetic field?

Answer: A magnetic field is the region around a magnet where magnetic force can be experienced. It is represented by magnetic field lines.

2. What are the properties of magnetic field lines?

Answer: 1. Magnetic field lines originate from the north pole and end at the south pole outside the magnet.

2. Inside the magnet, they move from the south pole to the north pole.

3. They never intersect.

4. The closer the lines, the stronger the magnetic field.

3. State 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 the current, the curled fingers show the direction of the magnetic field around the conductor.

4. How does the magnetic field differ for a straight conductor, circular loop, and solenoid?

Answer: 1) Straight Conductor: Concentric circles around the conductor.

2) Circular Loop: Magnetic field lines form concentric circles, concentrated at the center.

3) Solenoid: Produces a uniform magnetic field, similar to a bar magnet.

5. What is a solenoid? Write one use.

Answer: A solenoid is a coil of wire with many loops. When current flows through it, it produces a uniform magnetic field.

Use: It is used in electromagnets.

6. Define electromagnetic induction.

Answer: Electromagnetic induction is the process of generating an electric current in a conductor by changing the magnetic field around it.

7. State Fleming’s Left-Hand Rule.

Answer: Stretch the thumb, forefinger, and middle finger of your left hand perpendicular to each other:

i) Forefinger: Direction of the magnetic field.

ii) Middle finger: Direction of current.

iii) Thumb: Direction of force (motion).

8. What is the principle 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.

9. Name the components of an electric motor.

Answer: 

1. Armature

2. Commutator

3. Brushes

4. Magnets (or electromagnets)

10. What is the principle of an electric generator?

Answer: An electric generator works on the principle of electromagnetic induction: when a conductor moves in a magnetic field, an electric current is induced in it.

11. Differentiate between an AC generator and a DC generator.

Answer:

12. Why is the Earth’s magnetic field important?

Answer: The Earth's magnetic field protects us from harmful solar radiation and helps in navigation using a compass.

13. What is the role of a fuse in a circuit?

Answer: A fuse prevents overloading and short circuits by breaking the circuit when excess current flows.

14. Why is earthing important in household circuits?

Answer: Earthing prevents electric shocks by transferring excess current to the ground.

15. State Fleming’s Right-Hand Rule.

Answer: Stretch the thumb, forefinger, and middle finger of your right hand perpendicular to each other:

i) Forefinger: Direction of magnetic field.

ii) Thumb: Motion of the conductor.

iii) Middle finger: Direction of induced current.

16. What is the difference between overloading and short circuiting?

Answer: 

Overloading: Occurs when too many appliances draw excessive current.

Short Circuiting: Occurs when live and neutral wires come into direct contact, causing a sudden high current.

17. What is the function of a commutator in an electric motor?

Answer: The commutator reverses the direction of current in the coil, ensuring continuous rotation of the armature.

18. What are the applications of an electromagnet?

Answer: 

1. Lifting heavy iron objects in scrap yards.

2. Electric bells.

3. MRI machines in medical diagnostics.

19. What happens to the magnetic field strength if the current in a solenoid is increased?

Answer: The magnetic field strength increases with an increase in current.

20. Why are appliances connected in parallel in household circuits?

Answer: Appliances are connected in parallel to ensure they receive the same voltage and work independently.

21. How can the strength of an electromagnet be increased?

Answer: 

1. Increase the current through the solenoid.

2. Increase the number of turns in the coil.

3. Use a soft iron core inside the solenoid.

22. What is the advantage of alternating current over direct current?

Answer: Alternating current (AC) can be transmitted over long distances with minimal energy loss, whereas direct current (DC) is less efficient for long-distance transmission.

23. Explain the use of slip rings in an AC generator.

Answer: Slip rings maintain a continuous connection between the rotating coil and the external circuit, allowing the current to alternate direction.

24. Write two differences between a bar magnet and an electromagnet.

Answer: 

25. Why is the core of an electromagnet made of soft iron?

Answer: Soft iron enhances the magnetic field and loses its magnetism 

quickly when the current is switched off, making it ideal for temporary magnets.

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These questions cover key concepts and frequently tested topics, helping students prepare effectively for exams.

Thank you 🙏