Results of the mobile phone experiment

By Marcus Wilson 01/04/2010

Well, I have now done themobile phone experiment in a lecture.  The question was, is a bucket of water enough to shield the electromagnetic communication between a cellphone and the nearest mast?  So, I wrapped my phone in glad wrap (or cling film, for those who don’t live in NZ), put it in a sealable plastic bag (like those you are allowed to take through airport security), and then put it in a snaplock plastic container.  We did a quick control experiment, to check that it could receive through those layers of plastic, and then I held it in the middle of a bucket of water.

Did it ring.   No it didn’t.  Interesting result.  Took it out of the bucket and did another control expt.  Didn’t ring this time. Rather puzzling.  At this point the student who was phoning it realized he’d been phoning the wrong number.  So, let’s try again.. Back in the bucket. And it rang.   Not that I could hear it, but I could certainly feel the ‘vibrate’ part of the ringing through all that plastic.

Conclusion: A few centimetres of Hamilton tapwater isn’t enough.  

But what happens when we boost the conducticity of the water.   The more the conductivity, the more quickly an electromagnetic wave should be stopped.   So, I put some salt in there, and we tried again.   This time the phone didn’t ring.   

OK, so the method probably needs a bit of work to get it controlled properly, but hopefully it got the point across to the students about skin depth and how conductive materials kill off electromagnetic waves.

Finally, opened up the snaplock plastic container, poured the water out  (so much for that being waterproof), opened up the resealable bag and unwrapped the phone, which, I am pleased to report, is still working.

The Easter break is almost upon us, so don’t expect much blogging next week, but I shall be back

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