1.    Phenomenon of torch bulb and its inside view.

Take a torch and look inside its bulb. You can also take out the bulb with the help of your teacher. What do you notice? Do you find a thin wire fixed in the middle of the glass bulb in figure (b)? Now switch the torch on and observe which part of the bulb is glowing.
The thin wire that gives off light is called the filament of the bulb. The filament is fixed to two thicker wires, which also provide support to it, as shown in figure (b). One of these thick wires is connected to the metal case at the base of the bulb in figure (b). The other thick wire is connected to the metal tip at the centre of the base. The base of the bulb and the metal tip of the base are the two terminals of the bulb. These two terminals are fixed in such a way that they do not touch each other. The electric bulbs used at home also have a similar design. Thus, both the electric cell and the bulb have two terminals each.

2.    Phenomenon of  cell and bulb with different arrangment.
Take four lengths of electric wire with differently coloured plastic coverings. Remove a little of the plastic covering from each length of wire at the ends. This would expose the metal wires at the ends of each length. Fix the exposed parts of two wires to the cell and the other two of the bulb as shown in figure A and B.

(A) Electric cell with two wires attached to it

(B) Bulb connected to two wires

You can stick the wires to the bulb with the tape used by electricians. Use rubber bands or tape to fix the wires to the cell.
Now, connect the wires fixed to the bulb with those attached to the cell in six different ways as have been shown in figure C [(a) to (f). For each arrangement, find out whether the bulb glows or not. Write 'Yes' or 'No' for each arrangement in your notebook.

 Now, carefully look at the arrangements in which the bulb glows. Compare these with those in which the bulb does not glow.


3.    How to make a switch at home.
You can make a switch using two drawing pins, a safety pin (or a paper clip), two wires and a small sheet of thermo Col or a wooden board. Insert a drawing pin into the ring at one  end of the safety pin and fix it on the thermo Col sheet. Make sure that the safety pin can be rotated freely. Now, fix the other drawing pin on the thermo Col sheet in a way that the free end of the safety pin can touch it. The safety pin fixed in this way would be your switch in this activity. Now, make a circuit by connecting an electric cell and a bulb with this switch. Rotate the safety pin so that its free end touches the other drawing pin. 

The safety pin covered the gap between the drawing pins when you made it touch two of them. In this position the switch is said to be 'on' . Since the material of the safety pin allows the current to pass

through it, the circuit was complete. Hence, the bulb glows. On the other hand, the bulb did not glow when the safety pin was not in touch with the other drawing pin. The circuit was not complete as there was a gap between the two drawing pins. In this position, the switch is said to be 'off' as in figure. A switch is a simple device that either breaks the circuit or completes it. The switches used in lighting of electric bulbs and other devices in homes work on the same principle although their designs are more complex.

4    How to check the material is conducting or non-conducting.
    Would the bulb glow after completing the circuit shown, if instead of safety pin we use an eraser and key?

(i) No, the bulb will not light up. This is because an electric bulb lights up only when circuit is completed and eraser is a non-conducting material.

(ii) Yes, the bulb will light up. This is because an electric bulb lights up only when circuit is completed and key is a conducting  material which completed the electric circuit.