5B20.35 Radio in a Faraday Cage
Concepts
Gauss' law, Faraday cage
Overview
A radio is able to receive signals and make sound when outside a Faraday cage. The cage blocks the signals when placed over the radio, silencing it.
The cage gaps are on the order of centimetres, but the wavelength of an AM radio signal is on the order of hundreds of metres, so it is an effective Faraday cage.
Details
Equipment
- [1] Radio
- [1] Wooden block
- [1] Wire mesh
- [1] [AV Services] Microphone
Classroom Assembly
- Tune the radio to a station or loud static.
- Place the radio on the wooden block.
- Make sure the radio still makes audible sound when on the block.
Important Notes
- The radio's reception is direction-dependent. Try rotating the radio if you are unable to find a station or static.
Script
- Turn on the radio.
- Hold your microphone close to it so students can hear that the radio is producing sound.
- Put the wire mesh around the radio. It should become much quieter.
- Remove the wire mesh. The radio should get louder.
- Turn off the radio.
Additional Resources
References
- PIRA 5K20.35
Disclaimer
- Don't attempt this at home!
Last revised
- 2022
Technicals
- Different lecture halls have different radio stations that work. Images Theatre seems to have OK reception for AM 650.
- The old AM radio works well in most orientations, going from loud to silent when caged.
- The new AM/FM radio works well in FM, going from well-tuned to noisy when caged. It is less good in AM, often remaining tuned even when caged. The AM demo tends to work better with the radio lying on its side, but that must be tested before use.
Related AV
Related demos
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If you have any questions about the demos or notes you would like to add to this page, contact Ricky Chu at ricky_chu AT sfu DOT ca.