Danger at sea!

Bulbs
The warning flashes of lighthouses are vital to the safety of ships around the coastline. It was not until the mid-nineteenth century that lighthouses were fitted with electric light bulbs. Two men were responsible for the invention of the incandescent (white-hot) electric light bulb; Joseph Swan, an American and Thomas Edison, an Englishman. Edison's light bulbs contained a carbon filament within a vacuum. He first produced this on 21st October, 1879. By 1913, the tungsten filament (a type of metal) that is still used today had been introduced. Neon lights, like those pictured here, contain a gas. When electricity is passed through the gas, the tube glows. Electronic bulbs have also been developed. These produce only light - not heat - and so save energy.

Danger at sea!

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1. Take a piece of candle and make a hole down the centre. Use a paperclip to thread an elastic band through.

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2. Push the candle into a cotton reel and fix the band to the top with sticky tape. Also attach a bulb in a holder to the top passing the wires down through the candle.

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3. Use a long cardboard tube for your lighthouse. Cut a piece of polystyrene to fit the end and fix the candle through the middle, as shown.

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4. Insert the whole thing into the top of your lighthouse, allowing the wires to hang out of the end.

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5. Fix the polystyrene, candle and elastic band in place with two cocktail sticks. Push them right through the cardboard tube from one side to the other.

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6. Line a plastic cup with aluminium foil. Cut out a window to see the bulb. A
piece of  card with a hole to fit over the bulb will hold it in place.






Why It Works

electric energy

As the bulb puts the electrons to work by making it travel through a very long, thin wire called the filament, electric energy is transferred into light energy. Tungsten is a highly resistant metal that can become white hot without melting. Air is removed from the bulb and replaced by the harmless gas, argon. Electrons flow into the bulb when the circuit is complete and cause the wire to glow. Metal at the base of the bulb makes contact with the circuit. Bulbs can become very hot when switched on.

Danger at sea

5. Connect the wires to a battery and hide it under a papier mache "rock". Add cotton wool waves. Now twist the cotton reel around several times, let go and watch the warning light turn.








Bright Ideas

• Can you make a different kind of flashing light without switching the current off and on? Adapt the project to make the light revolve and flash in a different way. Try using coloured cellophane in the window to make a coloured light. Another way to make a flashing light is to use a circle of card, out of which slits like the spokes of a wheel have been cut. Place it in front of the bulb - then revolve the card when the bulb is glowing.
• Design and build a traffic light circuit so that the bulbs can be switched on and off in particular sequence. The sequence of change is different in various countries.
• What causes a fluorescent strip light to flicker? The answer is to do with the fact that mains electricity uses an alternating current (a current that varies all the time).
• Design a poster encouraging people to I turn lights off and save energy.