The following projects have been designed to be enjoyed.
1.Make an electric telegraph system.
2.Demonstrations with sound.
3.How to send messages in code?

1.Make an electric telegraph system.

You and a friend can make a simple telegraph set using materials that are easy to obtain.

You will need two electric buzzers, two 6-volt batteries , a roll of 18-gauge wire, two small blocks of wood , two thin strips of metal , and four round head screws.

Make two sending keys. For each ,use a block of wood as a base and a small strip of metal as a sender.If you are too young ask an adult to help you cut the metal from the lid of a tin can. Bind the sharp edges of the metal strip with adhesive tape so you do not cut yourself. Scrape or sandpaper the lacquer off the underside of one end to allow the electric current to pass through.

Screw one of the screws into one end of the block. This is your contact screw. Attach one end of the metal strip to the other end of the block with a second screw so that the unattached end of the strip is over the contact screw. Bend the metal upward so that it will not make contact with the screw unless pressed down.

Attach the wires as shown in the diagram. The batteries have positive and negative terminals, indicated by + and - signs. Be sure to connect the + ternimal of one battery with the - terminal of the other. Scrape off or push back the insulation at the end of a wire when making a connection so that the connection is made with bare wire. If your buzzers come with lead wires already attached , position the positive(red) leads as shown. Make each buzzer connection by twisting the bare ends of the connecting wires together. Then cover the connection with tape. To connect the wires to the sending keys , loop the bare wire under the head of each screw and then tighten the screw against the wood.

When both keys are pressed to the contact screws, a complete electrical circuit is formed. Electric current flows through the circuit, and the buzzers sound. To send mesages , use Morse code , keeping the key down longer for a dash than for a dot. Messages can be sent by only one person at a time. When your partner is sending a message , you must hold your key down so that there will be a continuous electric circuit.

2.Demonstrations with sound.

MAKE A SET OF MUSICAL GLASSES

You need:
8 drinking glasses(4 large and 4 small)
water
a pencil

Set the glasses in a row. Pour differents amount of water into the glasses.

Use the pencil to strike each glass near the top. Listen to the tones produced by the different lengths of the water columns in each glass.

Experiment with the amounts of water and the order of the glasses until they begin to resemble the sound of a musical scale.One such arrangement is shown in the diagram below. However , all glasses are different, so your result may look a little bit different than the diagram. If you have a test-tube rack and eight test tubes, the eight tubes also can be made to produce the tones of a musical scale.

SHOW HOW THE VIBRATIONS OF A TUNING FORK ARE PASSED ON AS THE FORK PRODUCES A SOUND.

You need:

4 table-tennis balls
4 strings , each of 8 inches(20 centimetres)
a tuing fork

With the tape, attach a string to each ball. The balls should swing freely from the strings.

Tie the free ends of the strings to a support , such as a towel rack. The balls should be about a quarter inch(0.5 centimetre) apart, and the string must not touch the wall or any other solid object.

Strike the tuning fork and hold it to your ear for a moment to be sure it is producing a sound. Then hold it close to the first ball. Watch how the balls swings as the vibrations from the tuning fork strike it .Notice how the vibration is transmitted to the other balls.

3.How to send messages in code?

Take a cylindrical object , such as a wooden dowel or the cardboard tube from a roll of paper towels , and a long , narrow strip of paper about half inch (1 centimetre) wide. Wind the paper around the cylinder, making sure that there is enough room between turns to print one letter.

Print your message across the length of the cylinder , moving all the way around it if necessary . Your scytale should look like the one above.

When the paper is unwrapped, the message will look like a long row of letters.

The person who receives the message must wrap the paper around a cylinder the same thickness as yours. Then the letters will line up properly, and the message can be read.

Thinkquest Participation 99Edition(http://www.thinkquest.org)
Entry from Royal College Port Louis Students
Mauritius