12. Shrink-Rays, Spectrum and String…

Thomas and Robin discuss (not) Shrink Rays and mysterious (not Alien) Space signals before getting on to the meat of the podcast: Teaching the EM Spectrum and using the simple question “How long is a piece of String?” to explore measurement, errors and uncertainty.

Thomas and Robin discuss why – when they are less likely than a podcast from the gym in January – media are still obsessed with Shrink Rays and mysterious (not Alien) Space signals. They soon move onto far more entertaining matters as they talk about teaching the EM Spectrum. Thomas tells us about his lovely “How long is a piece of String?” lesson. One of Robin’s favourites, it’s a great way of engaging reluctant students in the exploration of measurement, errors and uncertainty.

Time STamps

  • (not) Shrink Ray @ 2:50
  • Signals from Deep Space @ 4:50
  • Electromagnetic Spectrum @ 6:37
  • How Long is a piece of string? @ 14:18


It’s not a Shrink Ray: this is published in Science Magazine, but is a bit more accessible. Remember to tell us your examples of how putting “Laser” on the front of everything makes the students think anything is better. Whys is any signal from space immediately attributed to Aliens? The BBC should know better. Helen CK’s question on Facebook about how to teach the Electromagnetic Spectrum finally gets addressed. (Sorry for the delay, Helen!) Your ideas will be bigger and better than ours so please share. Equally, if there’s something you want to throw open to the community, just let us know (twitter, contact form, instagram). If you find your students reluctant to engage with uncertainty and measurement, then you will love Thomas’s “how long is a piece of string?” practical.

The EM Spectrum

Helen CK contacted us long ago asking for ways to teach the e-m spectrum. Thomas and Robin chatted about how they would teach it. Thomas from the future visits to remind them that the Electromagnetic Spectrum song by Emerson Foo and Wong Yann is not to be missed (below). N.B. Take care with this song because there are some spurious ones set up in YouTube to fool and embarrass unwary teachers. Thomas mentioned “any number of Doppler effect videos on YouTube”, this is a good one.

Please share ideas or successes on our Facebook Page – .  You can also message us via our website contact form at, Twitter @physicstp, email using  the address given in the podcast (if we remember) or by leaving a voice memo using WhatsApp or Telegram to the phone number in our Twitter profile, +44 7898 814716 (don’t call the number, nobody will answer, just hold down the microphone icon and speak your message). Don’t forget to tell us your name because we may use your audio in a future episode.

The music we use remains One legged equilibrist polka by Circus Homunculus.

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