Most of us have made or seen a tin can telephone at some point in our lives. This practical involves students varying the components which make up the telephone to see which type works best.
Equipment required (per set):
The aim of the practical is for the student to predict which variables will make the best telephone. The 'best' in this case can mean the loudness of the sound coming out of the receiver or the loss of volume. They can then make the telephone and test it with either a frequency generator, loudspeaker and oscilloscope or just by ear.
- Clean empty tin cans of varying size
- String of various lengths and thicknesses
- Frequency generator (optional)
- Small loudspeaker (optional)
- Oscilloscope (optional)
- Microphone (optional)
The cans to be used can be normal food cans of various sizes. Generally the bigger the base of the can, the more it vibrates when sound enters the can and these bigger vibrations travel down the string and into the receiver. Holes need to be drilled or pierced into the bottom of the cans in order to connect them together with string. These may be prepared in advance. Take care when piercing the holes and ensure that the metal around the hole is not sharp.
Students can vary the size of can, the length of string, thickness of string or the tension of the string. Higher ability groups may use a signal generator connected to a speaker which is placed near the opening of one of the cans. The receiver end can house a microphone attached to an oscilloscope. Students can vary the volume and frequency of the signal and see how much is transmitted through to the receiver by watching the trace on the oscilloscope.