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# Waves multiple choice quesion

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1. A progressive wave in a stretched string has a speed of 20m/s and a frequency of 100Hz. What is the phase difference of two points 25mm apart?
A zero
B PI/4
C PI/2
D PI

I originally worked out the wavelength by use of the wave equation, and got 0.2m.
I then converted the 25mm to m which is 0.025m. By dividing 0.2 by 0.025 I got 8. Meaning that the two points are 1/8 of a wavelength apart. I then changed this into radians by use of a diagram.
I was just wondering if there was any better way to do the last section after figuring out the wavelength as the way I've done it has confused myself
2. From speed and frequency you can calculate wavelength which comes out to be 0.2 meters or 200 mm As 200 mm gives a phase difference of 360 or 2pi rads then 25 mm will give pi/4 rads

I found this as a solution online.. I dont know if it makes sense or not i havnt learnt about phase difference
3. If you know that the two points are 1/8 wavelength apart,
one whole wavelength = 2π so then

phase = 1/8 x 2π
= 1/4 π

atleast thats how I'd do it, not sure if theres an easier way

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