नोट: इस लेख का हिंदी संस्करण भी उपलब्ध है।
Chapter 10: Electric Current and its Effects
Introduction
Electricity is a form of energy that is widely used in our daily lives. This chapter focuses on electric current, its effects, and how it is used in various devices.
Electric Current
- Definition: The flow of electric charge (electrons) through a conductor is called electric current.
- Electric Circuit: A closed path through which electric current flows is called an electric circuit.
- Components of an Electric Circuit:
- Cell/Battery: Provides the necessary energy for the current.
- Wires: Conducts electricity.
- Switch: Controls the flow of electricity.
- Bulb/Appliance: Uses electricity to perform work.
Symbols of Electrical Components
Electrical circuits are represented using symbols. Some common symbols are:
| Component | Symbol | ||||
|---|---|---|---|---|---|
| Cell | ( – | + ) | |||
| Battery | ( – | + – | + ) | ||
| Switch (Open) | ( —o o— ) | ||||
| Switch (Closed) | ( —o—o— ) | ||||
| Bulb | ( ⭕ ) | ||||
| Resistor | ( ⏦ ) |
Effects of Electric Current
Electric current produces various effects when it flows through a circuit:
a) Heating Effect of Electric Current
- When electric current passes through a conductor, it generates heat.
- This effect is used in electric iron, heater, toaster, geyser, and filament bulbs.
- Reason: When electrons move through a conductor, they collide with atoms, generating heat.
- Applications:
- Electric fuse: Prevents excessive current from flowing, thus avoiding damage to appliances.
- Electric bulbs: Filament inside the bulb glows due to heating effect.
b) Magnetic Effect of Electric Current
- When electric current flows through a wire, it creates a magnetic field around it.
- This effect was discovered by Hans Christian Oersted.
- Applications:
- Electromagnet: A coil of wire wound around an iron core, which acts as a magnet when current flows through it.
- Electric bell: Uses an electromagnet to produce sound.
- Electric motors: Convert electrical energy into mechanical energy.
Electromagnet and Its Uses
- Definition: A strong temporary magnet created by passing an electric current through a coil wound around an iron core.
- Uses:
- Lifting heavy iron loads in scrapyards.
- Used in electric bells and electric motors.
- Used in MRI machines in hospitals.
Electric Bell – Working Principle
An electric bell works on the magnetic effect of electric current. It consists of:
- Electromagnet: A coil of wire wound around an iron piece.
- Hammer and Gong: Strikes to produce sound.
- Contact Point and Spring: Helps in switching the circuit on and off automatically.
Working:
- When the switch is turned on, current flows through the circuit, creating a magnetic field in the electromagnet.
- The electromagnet attracts the iron strip, pulling the hammer towards the gong.
- The hammer strikes the gong, producing sound.
- The circuit breaks automatically, stopping the current.
- The process repeats rapidly, causing continuous ringing of the bell.
6. Precautions While Using Electricity
- Never touch electrical appliances with wet hands.
- Do not overload sockets with too many appliances.
- Use properly insulated wires to prevent short circuits.
- Always switch off electrical appliances when not in use.
Summary
- Electric current flows through a closed circuit.
- It has heating and magnetic effects.
- Heating effect is used in appliances like toasters and heaters.
- Magnetic effect is used in electromagnets, electric bells, and motors.
- Electric bell works on the principle of electromagnetism.
Class 7 Science : Electricity Circuit and Their Components Free Practice Quiz
1. Electric current in a circuit is the flow of:
Correct Answer: B) Electrons
Electric current is produced due to the movement of electrons through a conductor.
Electric current is produced due to the movement of electrons through a conductor.
2. The device used to open or close an electric circuit is called:
Correct Answer: C) Switch
A switch controls the flow of current by completing or breaking the circuit.
A switch controls the flow of current by completing or breaking the circuit.
3. Which component supplies electrical energy in a circuit?
Correct Answer: B) Battery
A battery provides electrical energy required for current to flow in a circuit.
A battery provides electrical energy required for current to flow in a circuit.
4. A material that allows electric current to pass through it easily is called:
Correct Answer: B) Conductor
Conductors such as copper and aluminium allow electric current to pass easily.
Conductors such as copper and aluminium allow electric current to pass easily.
5. Which of the following is an insulator?
Correct Answer: C) Plastic
Plastic does not allow electric current to pass through it, so it is an insulator.
Plastic does not allow electric current to pass through it, so it is an insulator.
6. Which component of a circuit produces light when current passes through it?
Correct Answer: C) Bulb
The filament inside the bulb heats up and glows when electric current flows through it.
The filament inside the bulb heats up and glows when electric current flows through it.
7. An electric circuit is said to be complete when:
Correct Answer: C) The path for current is continuous
Current flows only when the circuit forms a complete path.
Current flows only when the circuit forms a complete path.
8. The thin wire inside an electric bulb is called:
Correct Answer: B) Filament
The filament becomes hot and emits light when electric current passes through it.
The filament becomes hot and emits light when electric current passes through it.
9. Which of the following is commonly used as a conducting wire in circuits?
Correct Answer: B) Copper wire
Copper is widely used in circuits because it is an excellent conductor of electricity.
Copper is widely used in circuits because it is an excellent conductor of electricity.
10. If the switch in a circuit is open, the bulb will:
Correct Answer: C) Not glow
An open switch breaks the circuit, so electric current cannot flow.
An open switch breaks the circuit, so electric current cannot flow.
