Chapter-Chapter 3. Electric Circuits and Their Components Science Curiosity class 7 in english Medium CBSE Notes

Chapter 3: Electric Circuits and Their Components

Introduction: Electricity is an important part of our daily life. We use it for lighting, heating, running machines, and many other purposes. From fans and lights to mobile chargers and computers, everything depends on electricity. To use electricity properly, we need to understand how it flows and how different components work together in a circuit.

Electricity does not work randomly. It flows through a closed path called an electric circuit. Various components like cells, wires, switches, and bulbs are connected to form a circuit. Each component has a specific role.

This chapter covers the following topics:

• Electric current and its flow
• Electric circuit and its types
• Components of a circuit (cell, bulb, switch, wires)
• Open and closed circuits
• Symbols of electrical components
• Heating effect of electric current

Electric Current: Electric current is the flow of electric charges through a conductor. When electricity flows through a wire, it is called electric current.

For current to flow, there must be a source of electricity such as a cell or battery. Without a source, current cannot flow.

Example: When we switch on a torch, current flows from the battery to the bulb, making it glow.

Electric Circuit: An electric circuit is a complete path through which electric current flows. It consists of different components connected together.

If the path is complete, current flows easily. If the path is broken, current stops flowing.

Types of Electric Circuits:

• Open Circuit: The path is incomplete, so current does not flow.
• Closed Circuit: The path is complete, so current flows.

Example: When a switch is OFF, the circuit is open. When the switch is ON, the circuit becomes closed.

Components of an Electric Circuit: A circuit is made up of several important parts that work together.

• Cell: It is the source of electric energy.
• Bulb: It glows when current passes through it.
• Switch: It controls the flow of current.
• Connecting wires: They provide a path for current.

Key Point: Electric current flows only when the circuit is complete.

Symbols of Electrical Components: In real life, drawing actual pictures of electrical components again and again is difficult. Therefore, scientists use standard symbols to represent different components in a circuit diagram. These symbols make it easy to understand and draw circuits.

• Cell: Represented by a long and a short line.
• Battery: Combination of multiple cells.
• Bulb: A circle with a filament inside.
• Switch (Open): A gap in the line.
• Switch (Closed): Continuous line.
• Wire: Straight line.

Example: Instead of drawing a real bulb, we draw a simple circle with a filament symbol in diagrams.

Circuit Diagram: A circuit diagram is a representation of an electric circuit using symbols. It helps in understanding how components are connected.

Using circuit diagrams makes it easier to design and study circuits without confusion.

Heating Effect of Electric Current: When electric current passes through a conductor, it produces heat. This is known as the heating effect of electric current.

This effect is useful in many electrical appliances.

• Electric iron
• Heater
• Electric kettle

Example: When current flows through the filament of a bulb, it becomes hot and glows.

Electric Fuse: A fuse is a safety device used in electrical circuits. It protects appliances from damage due to excessive current.

It is made of a thin wire that melts when too much current flows, breaking the circuit.

Importance of Fuse:

• Prevents damage to appliances
• Avoids short circuits
• Ensures safety

Short Circuit: A short circuit occurs when current flows through an unintended path with very low resistance. This causes a sudden increase in current, which can be dangerous.

Example: When wires touch directly without resistance, it may cause sparks or fire.

Key Point: Proper use of circuit components and safety devices like fuse is essential to prevent accidents.

Electric Devices in Daily Life: Electricity is used in many devices that make our life easy and comfortable. These devices work on the basic principle of electric circuits.

• Fan – converts electrical energy into mechanical energy
• Bulb – converts electrical energy into light energy
• Heater – converts electrical energy into heat energy
• Mobile charger – converts electrical energy into stored energy

Each device uses a circuit in which current flows through different components to perform useful work.

Conductors and Insulators: Materials play an important role in electric circuits depending on whether they allow current to pass or not.

Types of Materials:

• Conductors: Materials that allow electric current to pass through them easily.
  Examples: Copper, aluminium, iron
• Insulators: Materials that do not allow electric current to pass through them.
  Examples: Plastic, rubber, wood

Example: Electric wires are made of copper (conductor) but are covered with plastic (insulator) for safety.

Importance of Conductors and Insulators:

• Conductors help in flow of current
• Insulators prevent electric shocks
• Both are essential for safe use of electricity

Care and Safety while Using Electricity: Electricity is very useful but can be dangerous if not used properly. Therefore, some safety measures should always be followed.

• Do not touch switches with wet hands
• Avoid damaged wires
• Do not overload circuits
• Use proper safety devices like fuse

These precautions help prevent accidents and ensure safe use of electricity.

Overall Understanding: An electric circuit is a complete path through which current flows. Different components like cell, bulb, switch, and wires work together to make devices function. Understanding these basics helps us use electricity safely and effectively.

Key Point: Electricity is useful only when circuits are properly connected and safety measures are followed.

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