-: MAKING A TRAFFIC LIGHTS :-

Traffic lights are used in big cities at major road crossings to make the vehicular movement smooth and avoid accidents. The red light is a signal of ‘stop’, green light is a signal of ‘go’ and orange light is a signal of ‘ready’. These lights are operated automatically. You can make a model of the traffic lights: 

*** MATERIALS REQUIRED ***

• Take two wooden strips-one (12 X 4 X 1)inch and the other (8 X 4 X 1)inch. Put them at right angles and fix them with the help of wood screws. 
• Put three bulb holders in a line and wire them in parallel. Insert the bulbs in the holders: top - red, middle - orange and bottom- green. 

• Fix the three wires from three bulbs at the base with drawing pins and put a fourth pin by pressing a U-clip under it. One end of it should be straightened so that it can be pressed against either of the three pins. This will act as a switch. 

• Connect the two dry cells in series, i.e. the positive terminal to negative of the other, to each bulb. 

• Connect the common wire from the bulbs to the positive terminal of the dry cell combination. Connect one wire from the negative terminal of the dry cell combination to the U-clip. Your model Is ready.
• Now, when you press the straightened edge of the clip against any of the three pins, one of the three bulbs will glow.