Today when we send information -- speech, words, numbers, or pictures -- to someone far away we can use the radio, telephone, television, fax machine, or a computer network. However, the need for telecommunication -- sending messages long distances -- did not originate in the twentieth century. Hundreds of years ago smoke signals, drums, and light beacons were used to send messages long distances. A century ago letters were carried by stagecoach or train and might take more than a month to go across the country.

The Telegraph
The telegraph was developed by Samuel B. Morse in 1832. Other inventors experimented with sending messages using electrical signals, but his was the first to successfully combine a simple code with a transmitting and receiving device. In a telegraph a switch opens and closes an electric circuit. In Morse's original design, the receiving device used an electromagnet, powered by the electric current in the circuit, to raise and lower a pen which made marks on a moving strip of paper. Morse also developed a code of dots and dashes -- long and short pulses to represent the letters of the alphabet.

Morse then had to find a way to send the electrical signal long distances. The signal grows weaker as it travels. The first working telegraph built by Morse worked over only 40 feet. By building more powerful generators and developing a system of relays, Morse was eventually able to send messages greater distances. By the end of the Civil War, in 1865, a network of telegraph lines linked the entire United States.

The Telephone
Many attempts were made to invent a machine that could transmit speech long distances. Sound waves themselves do not travel very far or very fast. The telephone, patented by Alexander Graham Bell in 1876, successfully reproduces speech by converting sound into electrical signals.

Modern telephones use the same basic principles as Bell's original phone. You speak into a mouthpiece, behind which is a transmitter. Your voice vibrates air molecules which in turn generate vibrations in a thin diaphragm inside the phone. This produces variations in the strength of the electrical current traveling through the telephone circuit which are precisely the same as the variations in the vibrations of your voice. The electrical current moves through the wire to the receiver.

At the receiving end, the electrical current travels through an electromagnet, which pulls on a diaphragm in the receiver. As the current in the circuit varies, the receiving diaphragm vibrates with the same wave pattern as the transmitter and reproduces the original sound.

Modern digital telephone systems take rapid samplings of sound and translate them into signal pulses carrying digital codes. With digitized systems, computer messages can be transmitted directly over telephone wires.

Today it is possible to mix together different forms of information -- speech, music, video signals, business data -- and send them over the same carrier signal. The information is sent as a series of on-off pulses and can be compressed to increase transmission capacity. Fiber optic cables transmit light signals and have even greater capacity than metal wires to carry information. A single glass fiber measuring 0.013 cm. (0.005 in.) in diameter can replace 10,000 metal telephone wires.

Today's networks of computers transfer all sorts of information -- voice, numerical data, text, pictures, and video images -- over telephone lines and fiber optic cables to people around the world.

Benchmarks for Science Literacy[7]

grades 3-5	Communication involves coding and decoding information. In any language, both the sender and the receiver have to know the same code.
grades 6-8	Electric currents and magnets can exert a force on each other. Information can be carried by many media, including sound, light, and objects. In this century, the ability to code information as electric currents in wires, electromagnetic waves in space, and light in glass fibers has made communication millions of times faster than is possible by mail or sound.
grades 9-12:	Almost any information can be transformed into electrical signals. A weak electrical signal can be used to shape a stronger one, which can control other signals of light, sound, mechanical devices, or radio waves. Moving electric charges produce magnetic forces and magnetic forces produce electric forces. The interplay of electric and magnetic forces is the basis for electric motors, generators, and many other modern technologies.

Tips on Working with Batteries and Bulbs
Experimenting with wires, batteries, and bulbs is essential to learning about electrical circuitry and electromagnets, and lots of fun, too! However, it is important to be careful and to teach campers to experiment safely.

• 1.5 volt "D" cell batteries are safe to handle as long as no more than 5 batteries are connected together in a series. There have been instances of people getting shocks from handling circuits where the total voltage was approximately 20 volts.
• Do not experiment with wall outlets.
• Never open any battery. Alkaline and lead acid batteries contain
• dangerous chemicals.
• Do not leave batteries in closed circuits for long periods of time. The wires can become very hot.
• Disconnect all circuits when you are finished. Separate the components to avoid draining the batteries.
• The uninsulated ends of the wires and the contacts on the batteries can get hot enough to burn very quickly. If any component begins to get warm, disconnect the circuit and let it cool.

Using battery holders and bulb holders can make it easier to experiment with circuits and also protect fingers from hot batteries and wires. Wires can be easily attached using the Fahnestock clips on the outside of the holders. When using bulb holders, the bulb must be screwed far enough into the holder so that the bottom of the bulb touches the metal plate beneath it. Electrical tape or masking tape also helps to hold together wires or components you want to connect more permanently.

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Experiment -- Build a Circuit

Materials
insulated wire (18 gauge)
flashlight bulbs
1.5 volt batteries
battery holders (optional)
bulb holders (optional)
hand lens
paper and pencils

Background for Instructors
All matter contains electrons, which will flow from a negatively charged source toward a more positively charged location. Current electricity is a flow of electrons that moves along a continuous and closed path called a circuit.

Electric current flows easily through certain materials called conductors. Almost all metals, such as silver, gold, aluminum, platinum, and copper are good conductors. Carbon, though not a metal, also is a conductor. Materials which do not permit electrons to flow easily are called insulators. Plastics, rubber, glass, cloth, and porcelain are good insulators.

Understanding circuits is essential to understanding how all electric equipment works, from flashlights to telephones, televisions, and computers. The challenge for campers is to arrange a battery, bulb, and wire so that the bulb lights. For this to happen there must be a complete circuit from one terminal of the battery through one wire touching the metal threads on the side of the bulb, out through the bottom of the bulb to the other battery terminal. Several arrangements will work. For example, the bulb can touch the positive or the negative terminal of the battery.

Some campers will build an operating circuit quickly and others may take longer. This requires some manual dexterity as well as thought. Working in pairs is recommended, because then there are four hands to hold the various components.

Objectives

• experiment with wires, batteries, and bulbs and practice working with battery and bulb holders

• observe that there must be a continuous path for electrons to flow along to complete a circuit

Procedure

• Each camper or pair of campers needs one bulb, one battery, and one wire (about 20 cm. long with the ends stripped).
• Experiment arranging the battery, bulb, and wire to light the bulb.
• When the bulb is lit, examine the arrangement. Which part of the bulb touches the wire? Which part of the bulb touches the battery? Which parts of the battery must be touched?
• Find several different ways to arrange the battery, bulb, and wire to light the bulb. What do these arrangements all have in common?
• Use a hand lens to observe the bulb. What is inside the glass? Where do the wires go? What is on the outside of the bulb?
• After one bulb is lit, try to light several bulbs at once. Experiment using two or three wires or two or three batteries together.
• Introduce the battery and bulb holders and incorporate them in the experiments. What parts of the battery and bulb touch the holder?

Background for Instructors
An electromagnet forms when electric current flows through a wire and produces a magnetic field around the wire. This essential link between electricity and magnetism was discovered by Hans Christian Oersted in 1820, when he observed that an electric current in a wire passing over a compass deflected the needle.

The magnetic field around a single wire is very weak. Coiling the wire around an iron core increases the strength of the electromagnet by concentrating the magnetic field. In this activity campers coil wire around an iron nail and run current through the wire to create an electromagnet strong enough to pick up small objects such as paper clips.

Electromagnets are found in many applications from doorbells to motors to television cameras and computer disk drives. The introduction to this section explains how electromagnets function in telegraphs and telephones. Here are a few more examples:

• Inside an electric motor, current flows into a coil of wire, and a magnetic field forms. Other magnets inside the motor are attracted or repelled by this magnetic field, causing the coil to spin, which in turn powers the machine.
• When you push the button on a doorbell, a circuit is completed and current flows through the wires to an electromagnet. This produces a magnetic field which pulls a metal arm against a metal bell to produce the ring.
• The play mechanism in a tape recorder uses electromagnets. Audio tape is covered with magnetic particles. When the magnetic particles on the tape pass through the play mechanism, they produce electronic signals that travel to an amplifier and into a speaker which reproduces the sounds.

Objectives

• demonstrate the connection between electricity and magnetism
• create an electromagnet
• experiment with an electromagnet to observe what variables affect the strength and longevity of the magnetic field

Procedure

• Try to use a nail as a magnet to pick up some small metal objects such as paper clips or brads.
• Take 1.5 meters of insulated wire and strip 2 cm. of insulation from each end.
• Wrap the wire tightly around a long iron nail leaving 15 cm. free at each end.
• Attach the two ends of the wire to the two poles of a battery. It is helpful to have a battery holder.
• Touch the point of the nail to a paper clip and lift the nail. Observe what happens. Is the paper clip attracted to the nail? Try picking up a string of paper clips?
• Experiment. What else can students pick up with the magnet? Wrap the wire around the nail fewer times or more times. Does it change how the magnet works?
• Disconnect the circuit. How long does the nail remain magnetized? What affects the strength and longevity of the magnetic field?

Note: Although this procedure is relatively simple, it can have its difficulties. If you're having trouble, try adding a second battery, using a different nail, or coiling more wire around the nail.

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Experiment -- Send a Message

Materials
two pieces of insulated wire at least 2 meters long
battery
battery holder (optional)
bulb
bulb holder
additional insulated wire
Morse Code charts (included)
paper and pencils

Background for Instructors
A telegraph works by changing words or voice into electronic signals. These signals are then sent through a wire by switching the current on and off or changing the intensity of the signal. At the receiving end the signals are changed back into letters or speech. In this activity campers use their light bulb circuit to send a message in Morse Code.

Morse Code is made up of a series of clicks that represent letters and numbers. It is written in dots and dashes. Mastering Morse Code takes time and practice, especially to differentiate between long and short pulses or where one letter ends and another begins. Encourage campers to start with very simple messages.

Objectives

• experiment with switching electric current on and off
• use electric signals to send a message
• translate a verbal message into a code of on-off signals and back into words

Procedure

• Have pairs of campers sit facing each other about 2 meters apart. One person will be the sender and the other the receiver.
• Assemble a light bulb in a holder with two long wires in front of the receiver.
• Stretch the wires to the battery that sits in front of the sender. Attach one of the wires to one pole of the battery.
• The sender will use the end of the second wire as a switch. As she touches it to the other pole of the battery, a circuit is completed, and the bulb lights. Moving the wire off the battery will make the bulb go out. This is a very simple switch.
• Experiment switching the bulb on and off by connecting and breaking the circuit.
• Use Morse Code (shown on the accompanying chart) to send a message. A short pulse of light represents a dot. A longer pulse represents a dash. Start with a very simple two letter word, such as HI. Suggest that campers count to five before starting a new letter. The receiver may want to write down the signals and/or letters as she receives them to keep track of the message.
• Try sending a more complex message or adding more wire to send the signal farther. How far apart can the partners be and still successfully send and receive a message?

A * -     B - * * *     C - *- *     D - * *   E *   

F * * - *    G - - *   H * * * *   I * *     J * - - -   

K - * -   L * - * *   M - -   N - *   O - - -   

P * - - *   Q - - * -   R * - *   S * * *   T -   

U * * -    V * * * -   W * - -   X - * * -   Y - * - -   

Z - - * *   

1 * - - - -   2 * * - - -   3 * * * - -    4 * * * * -   5 * * * * *   

6 - * * * *   7 - - * * *   8 - - - * *   9 - - - - *   0 - - - - -   

* * * *   * * = H I
- -   - - -   * - *   * * *  * = M O R S E

Footnotes
[7] AAAS. pp. 93, 97, 197-199.