5th class unit 8 electricity and magnetism | electric current | electric circuit

Unit:-8

               Electricity And Magnetism

 8.1 Electric Current 

Electric current is the flow of free electrons.In some materials like metals, electrons can move from one position to the other freely. If some energy is provided to these free electrons, they flow in one direction and cause current.

 This energy is provided to the electrons by battery. Battery is necessary for the production of electric current.

Battery converts chemical energy into electrical energy. This electrical energy pushes the charges and causes current. The electric current is measured in ampere (A) and is measured with a device named as ammeter.

Current can only flow through a close circuit. There are two types of circuits.

1. Closed circuit

2. Open circuit

Closed circuit: Closed circuit means that the wires are connected, so, there will be flow of current. Short circuit also refers closed circuit.

Open Circuit: Open circuit means the wires are disconnected so there will be no current flow.

8.2 Electric Circuit

Electric current needs a closed path to flow. The closed path through which current can flow is called an electric circuit, Electric circuit starts from positive end of the battery or cell and finishes at negative end of battery or cell. 

The circult contains many devices connected with each other. These devices are called as component of a circuit and are listed below.

1. Battery

It is most important component of a circuit. It provides electrical energy to the charges.

2. Wire

It provides a path for the motion of electric charges. The charges flow from one end of the battery to the other through the wires. 

3. Device

Device is a component which uses the electric energy carried by the wires. The example of devices are bulb, iron etc

4. Key

Key is a controlling component. It is used to switch on (open) and switch off (close) the "circuit.

The Electric current starts from positive terminal of the battery. After passing through the components, it ends at negative terminal of the battery. It's can be seen from the  following activity.

Fuse and its uses

Fuse is a short wire attached in a circuit to break the circuit when large amount of current flows through it. Fuse is attached with live wire.

 When large current flows through the circuit, the fuse melts down and disconnects the circuit. It saves the wiring, lives and appliances from damage.

The fuse has a maximum limit of current that can pass through it. This maximum limit is called rating of the fuse.

Now a days, fuses of different ratings are used. However, instead of fuse, the circuit breaker is also used.

Importance of Fuse

1. Fuse breaks the circuit in case of large amount of current flow and prevents the appliances from damage.

2. Fuse prevents short-circuiting and fire.

Types of fuse

There are two types of fuse used in daily life

1. Ceramics fuse

2. Glass cylinder fuse

The ceramics fuse is made up of ceramic with two metal terminals. The fuse wire is placed between these terminals.

The glass cylinder fuse is made up of a glass cylinder tube with two terminals. The terminals are at the corner of the glass tube. Fuse wire is placed in the glass tube.

Uses of fuse fuse

1. Fuse is used in household wiring.

2. It is also used in all electric appliances like televisions, etc. refrigerators, and ovens etc.

8.3 Lightning

Another example of static discharge on larger scale is lightning. Electric charge is formed in the clouds. When the charge becomes very large and the cloud moves closer to the ground, the static electricity is discharged in the form of lightning.

 During a rain storm, clouds develop regions of positive and negative charge. The negative charges are usually concentrated at the base of clouds while the positive charges are concentrated at the top.

Negative charges repel electrons on the ground beneath them, so, the ground beneath the clouds is positively charged.

 At first, electrons flowing out of the cloud towards the ground lose their energy in collisions with air molecules so they only travel a short distance. This creates a moving path so the next group of electrons can follow it and move on.

 This process is repeated until the path is closed to the ground. When this happens,Static build-up current is emitted electricity that which we call electricity.

Disadvantages of Lightning

Lightning is dangerous for human, animals and plants. It damage houses and buildings. It can set a fire in houses, buildings or forests. It can burn humans, animals and plants.