Chapter Guide
Chapter Overview
The chapter first investigates the magnetic effect of electric current.
Students observe that a current-carrying wire produces a magnetic field around it,
which can be detected using a magnetic compass. This phenomenon, first observed by
Hans Christian Oersted, demonstrates the connection between
electricity and magnetism.
Students then learn about electromagnets. A coil carrying electric
current behaves like a magnet, and inserting an iron core makes the electromagnet
stronger. The strength of an electromagnet can be increased by increasing the
electric current or the number of turns of the coil. Its magnetic poles can also be
reversed by changing the direction of current. The chapter also explains the practical use of electromagnets, including
lifting electromagnets used in cranes and scrap yards to lift and
release heavy iron and steel objects by switching the current ON and OFF.
Electromagnets are also used in devices such as electric bells, motors, fans and
loudspeakers.
The second major topic is the heating effect of electric current.
When current flows through a conductor, its electrical resistance causes some
electrical energy to be converted into heat energy. The chapter uses
nichrome wire to demonstrate this effect and explains that the
amount of heat produced depends on factors such as the material, thickness,
length of the wire, current and duration of current flow.
Learn Clearly
Important Concepts and notes
Important Concepts and Notes
1. Magnetic Effect of Electric Current
When electric current flows through a conductor, it produces a
magnetic field around the conductor. This is called the
magnetic effect of electric current.
A magnetic compass placed near a current-carrying wire shows a deflection.
This shows that electric current produces a magnetic effect.
2. Current-Carrying Coil as a Magnet
When a wire is wound into a coil and electric current is passed
through it, the coil behaves like a magnet. Such a magnet is called an
electromagnet.
An electromagnet has two poles: North and South.
3. Factors Affecting the Strength of an Electromagnet
| Factor |
Effect |
| Electric current |
Increasing the current makes the electromagnet stronger. |
| Number of turns |
Increasing the number of turns makes the electromagnet stronger. |
| Direction of current |
Changing the direction of current reverses the magnetic poles. |
| Iron core |
An iron core makes the electromagnet stronger. |
4. Uses of Electromagnets
Electromagnets are useful because their magnetic effect can be switched
ON and OFF by controlling the electric current.
- Lifting magnets used in cranes and scrap yards
- Electric bells
- Electric motors
- Fans
- Loudspeakers
5. Heating Effect of Electric Current
When electric current flows through a conductor, the conductor offers
resistance to the flow of current. As a result, some electrical
energy is converted into heat energy. This is called the
heating effect of electric current.
6. Nichrome Wire
Nichrome has relatively high electrical resistance and produces
considerable heat when current passes through it. Therefore, it is commonly used
as a heating element in electrical heating devices.
7. Factors Affecting Heat Produced
- Magnitude of electric current
- Material of the wire
- Thickness of the wire
- Length of the wire
- Duration for which current flows
8. Applications of the Heating Effect
| Electrical Device |
Effect Used |
| Electric heater |
Heating effect |
| Electric stove |
Heating effect |
| Electric kettle |
Heating effect |
| Electric iron |
Heating effect |
| Immersion rod |
Heating effect |
| Hair dryer |
Heating effect |
9. Electrical Safety
Excessive heating in electrical circuits can damage wires, plugs and sockets
and may even cause fires. Therefore, suitable wires, plugs and sockets should
be used according to the electrical requirements of the circuit.
10. Cells and Batteries
Cells and batteries are portable sources of electricity.
They can provide electrical energy to operate devices and can produce effects
such as light, heat and magnetism.
A cell generates electricity through chemical reactions
taking place inside it.
11. Voltaic or Galvanic Cell
A Voltaic cell, also called a Galvanic cell,
contains two metal electrodes made of different materials and an
electrolyte.
| Part |
Role |
| Electrodes |
Two different metal rods involved in the chemical reaction. |
| Electrolyte |
A liquid such as a weak acid or salt solution that helps the cell produce electricity. |
| Chemical reaction |
Produces electrical energy inside the cell. |
As the chemicals inside a Voltaic cell are gradually used up, the cell eventually
stops supplying electricity and becomes dead.
12. Lemon Cell
A simple electric cell can be made using a lemon, copper wire and an
iron nail. The copper wire and iron nail act as electrodes, while
lemon juice acts as the electrolyte.
Several lemon cells can be connected together to produce enough electrical
energy to make an LED glow.
13. Dry Cell
A dry cell is called a dry cell because its electrolyte is
present as a thick moist paste rather than as a freely flowing
liquid.
| Part |
Function |
| Zinc container |
Acts as the negative terminal. |
| Carbon rod |
Acts as the positive terminal. |
| Electrolyte |
Present as a moist paste around the carbon rod. |
A dry cell is generally a single-use cell. Once its chemicals
are used up, it cannot be reused by simply recharging it.
14. Rechargeable Batteries
Rechargeable batteries can be charged and reused many times.
They are commonly used in mobile phones, laptops, cameras, inverters and
vehicles.
Rechargeable batteries also have a limited life. After repeated charging and
use, they gradually wear out.
15. Battery Recycling
Used batteries should not be thrown into regular household garbage. They may
contain materials that can be harmful to people and the environment. Many
materials present in batteries can also be recovered and reused.
Therefore, used batteries should be disposed of through appropriate
e-waste and battery recycling facilities.
Quick Comparison
| Concept |
Key Point |
| Magnetic effect |
Electric current produces a magnetic field. |
| Electromagnet |
A current-carrying coil that behaves like a magnet. |
| Heating effect |
Electric current produces heat in a conductor. |
| Nichrome |
High-resistance material commonly used in heating elements. |
| Voltaic cell |
Produces electricity through chemical reactions. |
| Dry cell |
Uses a moist paste as its electrolyte. |
| Rechargeable battery |
Can be charged and reused multiple times. |
Key Points to Remember
- Electric current produces a magnetic effect.
- Electric current can also produce a heating effect.
- An electromagnet works only when electric current flows through its coil.
- Increasing current or the number of turns can increase the strength of an electromagnet.
- Reversing the current reverses the poles of an electromagnet.
- Nichrome is commonly used in electrical heating devices.
- A Voltaic cell converts chemical energy into electrical energy.
- A dry cell contains a moist paste as its electrolyte.
- Rechargeable batteries can be reused after charging.
- Used batteries should be disposed of responsibly through suitable recycling facilities.