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3. Electromagnets Current Producing Magnetic Fields Electromagnets vs Permanent Magnets Uses of Electromagnets Lifting magnets Relays DC motors (principles only)
Year 8 • Physics
Electromagnets
This lesson explains how electric current produces magnetic fields, how electromagnets work, how they differ from permanent magnets, and how they are used in lifting magnets, relays, and simple DC motors.
Lesson Objectives
- Understand how current produces magnetic fields.
- Explain how electromagnets work.
- Compare electromagnets and permanent magnets.
- Describe uses of electromagnets.
- Understand relays and DC motors (principles only).
1. Current Producing Magnetic Fields
When an electric current flows through a wire, it creates a magnetic field around the wire.
This means electricity and magnetism are closely linked.
[ Image Placeholder – Magnetic Field Around a Current-Carrying Wire ]
Real-life curiosity:
• A compass placed near a wire moves when current flows
• Turning off the current removes the magnetic field
• A compass placed near a wire moves when current flows
• Turning off the current removes the magnetic field
2. What Is an Electromagnet?
An electromagnet is a magnet made by passing electric current through a coil of wire.
[ Image Placeholder – Coil Around Iron Core ]
Key features:
• Works only when current flows
• Strength can be increased
• Can be turned ON and OFF
• Works only when current flows
• Strength can be increased
• Can be turned ON and OFF
Using an iron core makes the electromagnet much stronger.
3. Electromagnets vs Permanent Magnets
Electromagnets:
• Need electric current
• Can be switched on/off
• Strength can be changed
• Need electric current
• Can be switched on/off
• Strength can be changed
Permanent Magnets:
• Do not need electricity
• Always magnetic
• Strength cannot be changed
Real-life example:
Scrap yards use electromagnets, not permanent magnets.
4. Uses of Electromagnets
Common uses:
• Scrap metal lifting cranes
• Electric bells and doorbells
• Loudspeakers and headphones
• Relays and motors
• Scrap metal lifting cranes
• Electric bells and doorbells
• Loudspeakers and headphones
• Relays and motors
5. Lifting Magnets (Scrap Yards)
Large electromagnets are used to lift heavy iron and steel objects.
[ Image Placeholder – Scrap Yard Lifting Magnet ]
Why electromagnets are useful:
• Can lift heavy loads
• Can release metal by switching off current
• Can lift heavy loads
• Can release metal by switching off current
6. Relays (Principle Only)
A relay uses an electromagnet to control another circuit.
[ Image Placeholder – Relay Diagram ]
Why relays are important:
• Small current controls large current
• Improves safety
• Used in alarms and switches
• Small current controls large current
• Improves safety
• Used in alarms and switches
7. DC Motors (Principles Only)
A DC motor uses electromagnets to produce rotation.
[ Image Placeholder – Simple DC Motor Diagram ]
Basic idea:
• Current flows in a coil
• Magnetic forces cause turning
• Electrical energy → kinetic energy
• Current flows in a coil
• Magnetic forces cause turning
• Electrical energy → kinetic energy
Real-life examples: fans, toys, electric cars.
Practice Questions
A. Fill in the Blanks
- Current flowing in a wire creates a __________ field.
- An electromagnet needs __________ to work.
- Iron cores make electromagnets __________.
- Electromagnets can be switched __________.
- A relay uses an __________.
B. True or False
- Permanent magnets need electricity.
- Electromagnets can be turned off.
- Relays are used for safety.
- Motors change electrical energy into sound.
- Scrap yards use electromagnets.
C. Short Answer
- What is an electromagnet?
- Why is iron used in electromagnets?
- Give two uses of electromagnets.
- What does a relay do?
- What energy change happens in a motor?
D. Thinking Questions
- Why are electromagnets better than permanent magnets in cranes?
- Why does turning off current remove magnetism?
- Why are relays used in alarms?
- Why do motors rotate continuously?
- Why are electromagnets used in speakers?
✅ Show Answer Key
A. Fill in the Blanks
- magnetic
- electric current
- stronger
- on and off
- electromagnet
B. True or False
- False
- True
- True
- False
- True
C. Short Answer
- A magnet made using electric current.
- It increases magnetic strength.
- Cranes, doorbells (any two).
- Controls one circuit using another.
- Electrical to kinetic energy.
D. Thinking Questions
- They can be switched off to release metal.
- No current means no magnetic field.
- For safe control of large currents.
- Forces keep changing direction.
- To convert electrical signals into sound.
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