More physics with aluminium foil

By Marcus Wilson 09/08/2010 3

I gave a talk to the Junior Naturalists in Hamilton last Friday. It had some similarity to the talks I gave in June to the Osborne Days (year 12 and 13 school students), but I needed to change a few things because 1. The audience was younger, and 2. I wasn’t prepared to cart voluminous apparatus across from the University to Hamilton Gardens and back on a dark night.

The mobile phone in foil experiment works pretty well, and is simpler to do than the mobile phone in water experiment, and this time I extended it to a radio in aluminium foil. (It shouldn’t receive anything – the foil reflects all the waves and the radio goes quiet.)Now, I tried to test this a couple of evenings previously at home (to avoid embarrassing situations where your experiment doesn’t work.) But we’d run out of foil at home, and I had to improvise by sticking my pocket radio in a saucepan and putting the lid on.  This is when I got a bit of a startling result – on FM, the radio went silent as I expected. But on AM, it still continued to pick up stations while completely surrounded by metal.

3 Responses to “More physics with aluminium foil”

  • I’ll have to check (not having the saucepan at work with me right now) but I suspect it would. But why is AM getting in there and not FM? The wavelengths are much longer than the size of any hole (600 kHz is about 500 m, 100 MHz is about 3 m). I might go see whether it applies to all stations and all saucepans at various locations in the house?

  • Ahhh. Just noticed. You’ve only got half the post on sciblogs. Read the full thing on . I’ll have to ask Aimee what’s going on…

Site Meter