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# A level Physics waves watch

1. I am stuck on this question:

A detector is placed at a position where the intensity is a minimum. When it is moved a distance of 144m it passes through 9 maxima and reaches the ninth minimum from the starting point.

Calculate the wavelength of the mircrowaves,

Attachment 757986

Thanks
2. (Original post by Yodalam)
I am stuck on this question:

A detector is placed at a position where the intensity is a minimum. When it is moved a distance of 144m it passes through 9 maxima and reaches the ninth minimum from the starting point.

Calculate the wavelength of the mircrowaves,
The distance between two minima is half a wavelength in all stationary waves
So at the 9th minimum, it's been 9/2 wavelengths
3. This is a standing wave that's been formed. The wavelength of a standing wave is twice the distance between nodes/antinodes. So there are 9 maxima and minima within a distance of 144 metres, so 9 nodes and antinodes of the standing wave...
4. (Original post by have)
The distance between two minima is half a wavelength in all stationary waves
So at the 9th minimum, it's been 9/2 wavelengths
Why is this the case?
5. (Original post by Yodalam)
Why is this the case?
It's a fact you have to know about stationary waves.
If you want some reasoning, you have to think about how the stationary wave is formed from two waves.
If you draw a sine wave, and imagine that thats the wave moving in one direction, the maxina can occur at both the highest point and at the lowest point. That's half a wavelength difference in distance. So maximas and minimas are half a wavelength apart

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