Source: Teaching Electricity: Yes, You Can!

Got the Message?

Objective: to find out how a telegraph sounder works

      Today we take long-distance communication for granted. We just pick up a phone, punch a few buttons, and bingo! — we can speak to someone halfway around the world. While things like satellite links and microchips have improved the speed and quality of communication, the basic concept of instantaneous long-distance communication lies in Samuel Morse's telegraph system. In this activity, students will build their own electromagnetic telegraph and send each other messages.
     In this activity, students will build their own electromagnetic telegraph and send each other messages.

     • ruler

Getting Started
1. Have the class sit quietly. Tell students that you are going to send them a secret message that they have to decode.

2. Using a ruler, make three very fast taps followed by three slow taps then three very fast taps on the desk. Ask: Who knows what the message is? (Some students might recognize the pattern as SOS.) Explain to students that SOS was chosen as the universal distress signal in Morse code because this combination of letters creates a distinct and unmistakable sound pattern. The Morse code is a way of sending messages over long distances using a device called the telegraph.

Science in Action
Divide the class into groups of four. Tell students that they will build a simple Telegraph Tapper and then send a message to other members of their group. Distribute the activity sheet and the Morse Code Conversion Chart to each student.

Build a Telegraph Tapper
Materials (per group of four students)

  • 3-inch steel nail
  • fist-sized lump of clay
  • 20-inch-long piece of thin, insulated wire, with ends stripped bare (available at a hardware store or electronics store such as Radio Shack)
  • 5- by 1-inch strip of index card
  • steel thumbtack
  • 3 or 4 large books or wooden building blocks
  • "D" cell
  • tape

1. Wrap at least 40 turns of wire around the middle of the nail to form the electromagnet. Make sure to leave at least 5 inches of wire on each end of the coil to attach to the "D" cell.

2. Push the thumbtack through the middle of the index card strip, about inch from one end.

3. Set up your telegraph sounder as shown. Make sure the nail rests directly under the thumbtack. The gap between the two should be about 1/8 inch.

4. Securely tape one end of the wire coiled around the nail to the flat end of the "D" cell. Briefly touch the other end of the wire to the bumpy end of the cell. The electromagnet will attract the thumbtack and make a "click." Lift the wire and the thumbtack should release. (If the thumbtack stays stuck to the nail, the gap between the two is too small. Adjust the nail in the clay to add more space between the two. If the thumbtack doesn't stick to the nail, the gap is too wide.)

Questions to Think About
1. Why do you need to have at least 40 turns of wire on the nail to make the sounder work? (You need a strong magnetic field to pull the nail head and thumbtack together.)

2. Could a brass paper fastener replace the steel thumbtack in the sounder? (no) Why? (Brass is not magnetic.)

3. Why do you need to adjust the position of the nail head before sending your messages? (To get the clicking sound, you need to have a significant distance between the nail head and the thumbtack.)

Safety First
Tell students not to touch the "D" cell for more than 10 seconds at a time because they could burn their fingers.

Science Fair Project Idea
Long-Distance Tapping
The real test of any communication device is to send messages over a distance! Challenge students to build a system that would work between rooms at a distance of more than 20 feet. (Students may need to use a 6-volt lantern battery instead of the "D" cell.)