Path Difference: Why a Cold Spot Forms at S

AI Thread Summary
A cold spot in microwaves occurs due to destructive interference, where waves arriving at point S are out of phase. The path difference is calculated by subtracting the distances traveled by the waves reflecting off different surfaces. In this case, the calculation involves determining the total distance traveled by each wave and then finding the difference. Dividing the path difference by the wavelength helps identify the number of wavelengths in that difference, which is crucial for understanding the interference pattern. Understanding these principles clarifies why cold spots form in microwave fields.
Luke1121
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I was doing a past paper earlier and i got a question about cold spots in microwaves and i needed to calculate path difference the question was:

---------|------->S<---------|--------- Explain why a cold spot is formed at S
18cm | 6cm. 12cm | 30cm

The question showed the waves reflecting off the top and sides of the microwave which are shown by the -|-

It was 4 marks so a calculation should be done and i did (30+12)-(18+6) then i didnt know what to do, i then found out you are supposed to divide (30+12)-(18+6) by 12. But I am not really sure why, can anyone explain why? Thanks
 
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What is the wavelength or frequency of the microwaves?
 
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