Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Cut a small strip of sandpaper for each lab group.
2. Photocopy enough of the Supplemental Materials in the Further Extensions section for each student.

Safety Precautions

While the batteries are not harmful, small shocks are possible. Do not complete the circuit with the battery for more than ten-second intervals. Since there is very little resistance in the wires, the battery can discharge quickly and become very hot if it is connected for a longer duration. Care should be taken when wrapping and unwrapping the wire. The pointed ends of the wire are hazardous to eyes. Wear safety glasses. Please follow normal laboratory safety guidelines.

Lab Hints

• If the iron strip is positioned too close to the nail head, it may not “detach” from the nail once the circuit is broken by the contact key. Ensure that students test their telegraph before attempting to send Morse code messages, so the iron strip taps the top of the electromagnet and does not get stuck.
• In Morse code, each character (letter or numeral) is represented by a unique sequence of dots and dashes. The duration of a dash is three times the duration of a dot. Each dot or dash is followed by a short silence, equal to the dot duration. The letters of a word are separated by a space equal to three dots (one dash), and two words are separated by a space equal to seven dots. The dot duration is the basic unit of time measurement in code transmission. Have student groups decide on how long their basic unit of time should be.

Teacher Tips

• This is a great activity to include in a unit about electromagnetism and to help students make connections with the influence of science and engineering on technological advances.

Further Extensions

Supplemental Material: International Morse Code

1. The length of a dot is one unit.
2. A dash is three units.
3. The space between parts of the same letter is one unit.
4. The space between letters is three units.
5. The space between words is seven units.
   {14079_Extensions_Figure_4}

Answers to Prelab Questions

1. What is an electromagnet?

   An electromagnet is a magnet created by coiling a current-carrying wire around a metal core.

2. How long was the wire that Joseph Henry sent the signal through?

   The wire was a mile long.

3. Examine the Morse code alphabet provided in the Supplemental Materials in the Further Extensions section. How would you signal “The telegraph” in Morse code? Use “.” for dots, “-“ for a dash, and separate letters with a space and words with “/”.
   {14079_PreLabAnswers_Figure_5}

Answers to Questions

1. In your own words, explain how the electricity flows in the circuit and why the iron strip is attracted to the nail.

   Once the terminals in the battery are connected due to a complete circuit being formed, the electricity (electrons) flow from the battery (negative terminal) along the wire. The circuit is complete when the contact key is closed. Therefore, the charge flows from the battery, through the contact key, through the electromagnet, and then back to the battery.

2. If the system has a light bulb added does it still work? If not, why do you think that is?

   Student answers may vary. The telegraph did not work because the iron strip would no longer make contact with the electromagnet when the circuit would close. This is due to the light bulb taking energy away from the rest of the circuit and therefore weakening the electromagnet.

3. Where you able to decode your lab partner’s message? What difficulties did you encounter when trying to do this? How would you improve the design?

   Student answers will vary. To improve the effectiveness of communication by Morse code, a buzzer could be added to the circuit for clearer interpretation of messages.

4. Why do you think the development of the telegraph led to an increase in the rate of industrialization?

   Student answers may vary. The speed in communication within the scientific community allowed for collaboration to occur earlier than before. More people working together at the same time led to faster industrialization.

5. How have modes of communication improved today?

   Student answers may vary. Today, the internet and devices such as computers and smartphones have vastly increased the speed at which information is shared and has also changed the way we communicate through social media, instant messaging and video streaming.

Introduction

In today’s modern age we are accustomed to light-speed telecommunication thanks to smartphones, the internet, and ever faster computers… but it was not always this way! Create one of the first forms of “fast” telecommunication with the construction of your very own telegraph. Discover the usefulness of the electromagnet, send messages with Morse code and gain an appreciation for the speed at which we send and receive information today.

Concepts

• Circuits
• Faraday’s law
• Electromagnetism
• Morse code

Background

The word telegraph is derived from the Greek words tele, meaning far, and graphein, meaning write, and is defined as any system that allows for transmission of encoded information by signal across a distance. The term telegraph, however, is most often used when referring to the electrical telegraph that was developed in the 19th century. In 1819, Hans Christian Oersted (1777–1851) discovered that a current-carrying wire could deflect a magnetized compass needle. In 1824, British inventor William Sturgeon (1783–1850), discovered the electromagnet. An electromagnet is simply a current-carrying wire coiled around a ferromagnetic material, such as a piece of iron. It was found that a current-carrying wire wound around the metal core would create a magnet whose magnetic properties could be switched on or off by simply switching the current on or off. The scientific community continued to improve on the apparatus. In 1830, Joseph Henry (1797–1878) successfully implemented an electromagnet into the telegraph, and demonstrated the possibility of using a telegraph for long-distance communication. Henry sent an electric current over a mile of wire to activate an electromagnet that caused a bell to strike. This was the first iteration of the electric telegraph.

In the next couple of decades, Samuel F.B Morse (1791–1872) and his partner Alfred Vial (1807–1859) capitalized on Henry’s telegraph for commercial use. They invented the simple operator key and the famous Morse code, which enabled operators to communicate over a series of “dots and dashes” and eventually over the sound of clicks produced by an electromagnet-activated key. Telegraph systems quickly spread through the United States and Europe. Circuitry advancements by the likes of Jean-Maurice-Emile Baudot (1845–1903) and Thomas Edison (1847–1931) allowed for the simultaneous transmittance of multiple messages on the same line. The telegraph was a major factor in the rapid rate of industrialization in the second half of the 19th century known as the Technological Revolution.

Experiment Overview

The goal of this laboratory activity is to gain an understanding of how a telegraph system works by building a simple wired telegraph. The circuit components required for the system to function are studied as well as the electromagnetic phenomena that allowed for more efficient long-distance communication.

Materials

Prelab Questions

1. What is an electromagnet?
2. How long was the wire that Joseph Henry sent the signal through?
3. Examine the Morse code alphabet provided in the Supplemental Materials in the Further Extensions section. How would you signal “The telegraph” in Morse code? Use “.” for dots, “-“ for a dash, and separate letters with a space and words with “/”.

Safety Precautions

While the batteries are not harmful, small shocks are possible. Do not complete the circuit with the battery for more than ten-second intervals. Since there is very little resistance in the wires, the battery can discharge quickly and become very hot if it is connected for a longer duration. Care should be taken when wrapping and unwrapping the wire. The pointed ends of the wire may be sharp. Wear safety glasses. Please follow normal laboratory safety guidelines.

Procedure

1. Obtain the iron nail and 5-m length of magnet wire.
2. Tightly wind the magnet wire up and down the length of the nail leaving about 8 cm of free wire on each end. Note: Make sure the wire is wound as tightly as possible while taking care not to break the thin wire.
3. Sand about an inch of insulation off the free ends of the wire (see Figure 1).
   {14079_Procedure_Figure_1}
4. Push the pointed tip of the iron nail into the foam base so that it protrudes about 3 cm from the surface of the foam base. The nail should be placed about 5 cm from the short edge of the foam base.
5. Obtain the iron strip. Using pliers, bend the strip at a 90-degree angle at a point 2 cm from the end. The strip will look like an “L.” Now, 3 cm from the first bend, bend the long side of the “L” away from the short side at a 90-degree angle (see Figure 2).
   {14079_Procedure_Figure_2}
6. Position the long end of the strip over the iron nail, as seen in Figure 2. Tape the 2-cm end of the iron strip to the surface of the foam base as tightly as possible so that it stays in place. Note: Bend the strip as needed in order for the long end to not make contact with the head of the nail.
7. Take a 1-kg weight (hooked weight, textbook or anything relatively heavy) and place it on top of the 2-cm end of the iron strip. This is to ensure that the strip does not move underneath the tape.
8. Collect the contact key, two 1.5 V D-cell batteries, 2 D-cell battery holders, and alligator clip wires.
9. Place the batteries in the battery holders and connect them to each other.
10. Unscrew the red and black knobs off of the contact key and set them aside.
11. Using an alligator clip wire, connect a free electromagnet wire to the post of the contact key (see Figure 3). Note: Some contact keys may be slightly different than the diagram.
    {14079_Procedure_Figure_3}
12. Connect the remaining free electromagnet wire to the battery pack as seen in Figure 3.
13. Connect the other end of the battery pack to the remaining metal post on the contact key as seen in Figure 3.
14. Press down on the contact key and observe the motion of the iron strip above the electromagnet. If the strip does not move, adjust the height of the electromagnet or adjust the angle of the iron strip. Note: There should only be a few millimeters of distance between the iron strip and the head of the nail.
15. Adjust as needed until the iron strip consistently makes contact with the electromagnet when the contact key is pressed and so that when the contact key is released, the iron strip no longer makes contact with the iron nail. Note: The right configuration should allow for consecutive taps of the iron strip onto the iron nail.
16. One of the lab partners should use the Morse Code alphabet provided in the Supplemental Materials to send a message with the telegraph while the other lab partner attempts to decode the message. Begin with a one-word message for practice. Once mastered, try a short sentence or phrase.
17. If time allows, add a miniature light bulb to the circuit between the battery and contact key. Make not of any observations when attempting to use the Telegraph System again.

Student Worksheet PDF

14079_Student1.pdf