This chapter discussed important components of electric circuits, how electrical energy is produced and used to operate electrical systems. Given below are short notes on the chapter Electricity.
Electricity
Electricity is used in many areas of our daily life. It helps in lighting homes, running fans and ACs, cooking food, using mobile phones, watching TV, and running machines like pumps and cranes. It is also used in transport like trains and lifts. Electricity makes our life easy and comfortable.
Sources of Electricity
Electricity is produced in different ways such as:
- Water (hydropower)
- Sun (solar energy)
- Wind (wind energy)
- Coal and gas
This electricity reaches our homes through wires.
👉 For experiments, we use cells and batteries because they are safe.
Electrical Components
Electric Cell
An electric cell is a source of electricity. A cell provides energy to make devices work.
It has two terminals:
- Positive (+)
- Negative (–)
The metal cap is the positive terminal and the flat base is the negative terminal.
Battery
When two or more cells are connected together, it is called a battery. Batteries give more power and last longer.
Cells are connected in such a way that:
- Positive of one → Negative of another
Electric Lamps
(a) Incandescent Lamp
It has a thin wire called filament. When current passes, the filament heats up and glows. If filament breaks, bulb does not glow (fused).
(b) LED (Light Emitting Diode)
LEDs has no filament. They have two terminals (long wire = positive, short wire = negative). These use less electricity and are more efficient.
Secret behind multi colour LEDs
There are special chemicals filled inside LEDs. These chemicals produce light when current is passed through them. For example:
- Gallium arsenide (GaAs) → used for red light
- Gallium phosphide (GaP) → used for green light
- Gallium nitride (GaN) → used for blue light
By changing the material, we get different colours of light.
Simple Electric Circuit
A circuit is a complete path for electric current to flow. A simple circuit has Cell or battery, Wires and a Bulb. The Bulb glows only when the circuit is complete.
Open and Closed Circuit
- Closed circuit: A circuit in which current can flow from one terminal of cell/battery to another without any break is called as closed circuit.
- Path is complete → current flows → bulb glows
- Open Circuit: A circuit in which current can not flow from one terminal of cell/battery to another due to any issue is called as an open circuit.
- Path is broken → no current → bulb does not glow
👉 Current flows only in a closed circuit.
Question. Predict whether bulb will glow or not.
Electric Switch
A switch is used to start or stop current in a circuit. Switch helps us control electricity.
When switch is on, circuit is closed and current will flow. If switch is off, circuit is open and current will not flow.
- ON → circuit closed → current flows
- OFF → circuit open → no current
Circuit Diagram
Instead of drawing real objects, we use symbols. This drawing is called a circuit diagram. It makes circuits easy to draw and understand.
Circuit Diagram of Bulb and LED Lamp
Conductors and Insulators
- Conductors: Materials that allow current to pass are called conductors. For example- Metals like copper, aluminium.
- Insulators: Materials that do not allow current to pass are called insulators. Plastic, rubber, wood.
Wires are made of metal (inside) and covered with plastic (outside).
Safety in Electricity
Electricity can be dangerous. Precautions are needed for safety.
- Do not touch switches with wet hands
- Do not use damaged wires
- Do not experiment with main electricity
- Always use cells/batteries for experiments.
Types of Current
- DC (Direct Current) → from cells/batteries
AC (Alternating Current) → from power supply (home electricity)
👉 AC is used for big appliances, DC for small devices.