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physics Waves question

https://gyazo.com/f5d8ec4217a2ccf2067c94b12d71ae00

Answer is 65 degree but how, question b i
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Original post by standardolo
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My first thought is that the dashed normal lines are formed to a triangle. If we consider it as such, the angle i is a piece of cake. For the first angle you can use the equation incience angle = angle of reflection, as the ray hits on an even wall of the fibre first before reflection. The second angle 30° is given. The third angle i can be calculated by the angle sum. If you are still struggling, let me know.
(edited 2 years ago)
Original post by standardolo
https://gyazo.com/f5d8ec4217a2ccf2067c94b12d71ae00

Answer is 65 degree but how, question b i

If you look in the top left hand corner at the 85, the ray has been reflected which means the angle next to it is also 85 (as when light reflects it reflects at the same angle it was incident at).

Then look at the whole triangle: you have the angle 30 at the bottom, the angle 85 where it was reflected, and the angle i. Simply do 180 - 85 - 30 to find the missing angle i

Hope this helps :smile:
Original post by standardolo
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Original post by standardolo
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Original post by standardolo
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Bumping your own thread increases the reply count which makes it look like it's already been answered... there was no risk of your thread dropping off the first page
Original post by Emily.Violet
If you look in the top left hand corner at the 85, the ray has been reflected which means the angle next to it is also 85 (as when light reflects it reflects at the same angle it was incident at).

Then look at the whole triangle: you have the angle 30 at the bottom, the angle 85 where it was reflected, and the angle i. Simply do 180 - 85 - 30 to find the missing angle i

Hope this helps :smile:

Exactly my thought! :smile: calculating with a traingle makes everything easier.

Original post by Joinedup
Bumping your own thread increases the reply count which makes it look like it's already been answered... there was no risk of your thread dropping off the first page

So true! When I saw this thread in the latest I thought that it is answered, just my curiosity led me here. Otherwise I wouldn't have taken a closer look. Bumping is really not a good idea. Patience is the key word!

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