Electric Circuit

·         Describe the flow of electric current in an electrical circuit.

·         Describe fuse and its importance in any electric circuit.

·         A battery cell is used in different devices such as torch, toys, watches and many appliances.

·         One end of the battery cell is positive and other is negative. There is deficiency of electrons at the positive end and abundance of electrons at the negative end. When two ends of a battery cell are connected through wire, electrons start flowing from the end where they are in abundance towards the end where they are less in number.

·         This flow of electrons is called as electric current.

·         Since electrons carry charge so we can say that an electric current is the flow of charges.

·         A fuse is inserted in the circuit to protect the appliance from burning.

·         Each fuse is rated for maximum value of current.

·         If more current passes through it, the fuse blows out i.e. flow of charges stops. In this way, the electric appliances safe.

Torch bulbs, battery cells, switches, glass plates, a thin metallic wire of low melting point, connecting wires of different lengths, textbook

·         Ask some questions to recall then previous knowledge of the students about electrical circuit:

1.       What is an electric circuit?

2.       Do you think that straight wire is a circuit?

3.       What do you need to make a circuit?

4.       What are the sources of electricity?

5.       Have you heard about fatal accidents and fires caused by electricity and people getting electric shocks?

6.       Is it due to unsafe use of electricity?

·         Let the students discuss the questions. Write the key points of their discussion on the board and announce the topic i.e. safe use of electricity.

·         Divide the students into groups.

·         Provide each group with a battery cell, a torch bulb with holder, a switch and three pieces of connecting wires.

·         Draw a circuit diagram on the board.

·         Ask the students to construct an electric circuit according to the diagram. Direct them to keep the switch open.

·         Ask them why the bulb is not glowing. Ask what do they think would happen if the switch is closed. Will the bulb glow?

·         What causes the bulb to glow?  After students’ response, inform them that the bulb does not glow, inform them that the bulb doesn’t glow if the switch is open. Such a circuit is called incomplete or open circuit.

·         Ask them to close the switch and tell them that the bulb glows when the circuit is complete. The electric circuit becomes complete or closed circuit when the switch is closed.

·         After this activity, tell the students that electric current can only flow through a closed circuit. No electric current flows when the circuit in open.

·         Divide the students into groups.

·         Give them a battery consisting of 2-3 cells, a piece of thin wire with low melting point, bulb holder, switch and connecting wires.

·         Ask them to complete the circuit as In activity 1.

·         Now ask them to connect the thin wire with low melting points in the circuit.

·         Ask the students:  Did the thin wire burn? What is the reason?

(Expected response: because the current that passes through wire is more than its limit)

·         Ask: How the electric appliances are saved by using fuse?

(Expected response: Fuse doesn’t allow excess amount of current to flow through the appliance)

·         After getting the students’ response, tell them that if the current more than the rated value of fuse passes through the fuse, it blows out and electric circuit breaks. In this way the electric appliances is saved from burning.

·         The current flows in a circuit when the switch is closed. It is called complete circuit.

·         The current doesn’t flow in a circuit when the switch is open. It is called incomplete circuit.

·         The battery is a source of electricity.

·         A fuse is used in the circuit of electric appliance to save it from burning.

Ask the following questions:

·         What causes the bulb to glow when the circuit is complete?

·         Why does the bulb not glow if there is no electric cell in the electric circuit?

·         What is the source of electric current in the circuit?

·         Does the bulb glow if the electric cell in the circuit is reversed?

·         What happens if the fuse is not used in the appliance?

·         What is the role of connecting wires in the circuit?

Make a list of electric appliances at your home in which you think the fuses have been used?