Eighth Grade · Science · week 26

Communication-device design

Design a simple communication device or code using circuits, sound, or signal concepts from this unit, and explain the physics behind it.

A communication device turns information into a signal that can travel, then back into information. A string telephone -- two cups connected by a taut string -- carries sound as vibrations through the solid string, a very efficient medium over a short distance, as long as the string stays tight and untouched.

A telegraph-style circuit (a battery, a switch, and a buzzer) can send information using a code of short and long presses, similar to Morse code. This is a digital-style idea: at any instant the switch is in one of two states, and the pattern of pulses carries the message.

📋 For the teacher
Teach it (10–15 min):
  • Build a real string telephone together if materials allow, and test what happens when the string goes slack or is touched.
  • If a simple buzzer-and-switch circuit is available, practice sending a short coded message.
  • Connect this week back to sound needing a medium (week 20) and analog versus digital signals (week 23).
Talk about it:
  • Why does a string telephone depend on the string staying taut and untouched?
  • What makes a switch-based code a digital-style system?

Mastery looks like: They explain how a string telephone or a coded circuit transmits information, connecting the design to sound or signal physics.

Common stumbles: Assuming a string telephone works through the air rather than the string; not recognizing a switch-based code as digital.

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