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# Exam Question on Waves (Stuck) - Depth OCR

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1. Question: Why can't BBC Radio 1 be broadcast on 98.9 FM over the whole country, using a large number of local transmitters all tuned to the same frequency?

(Hint - think about superposition, and constructive and destructive interference).

This was a sample question given by my teacher.

I thought that different waves from different transmitters would out of of phase from one - another so the waves would interfere destructively in certain regions so the resultant waves are smaller, and in certain regions where the phase different is 180º, this would mean that a shadow would be created where no one can tune into the radio station.

Is this right?
2. That seems good, but the last bit is not completely right. For example if there are 3 waves coming to a point and lets call them A, B and C. If A=1m, B=2m and C=-3m, then at that point the A+B+C=0, the waves A,B,C aren't in phase, but they aren't in antiphase either. So it might better to say, some regions the waves will cancel out completely leaving a "shadow", as you mentioned.

Also, if this was an exam question and worth more than a couple marks, I would add another line describing the superposition principle. E.g. When two or more waves superimpose at a point the resultant displacement is the sum of the individual waves.

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Updated: June 8, 2016
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