PHYA2 - Optics help?

I have looked at the markscheme for this question and noticed they did 180 - 90- critical angle. Why did they do this? to give the refractive angle?

& If so could someone draw a diagram to show this refractive angle as I cant just picutre the 180 degree angle they are taking 90 and 80 degrees from :frown:

http://filestore.aqa.org.uk/subjects/AQA-PHYA2-W-QP-JUN11.PDF

Reply 1

Joinedup

20

Original post by AhmedDavid

I have looked at the markscheme for this question and noticed they did 180 - 90- critical angle. Why did they do this? to give the refractive angle?

& If so could someone draw a diagram to show this refractive angle as I cant just picutre the 180 degree angle they are taking 90 and 80 degrees from :frown:

http://filestore.aqa.org.uk/subjects/AQA-PHYA2-W-QP-JUN11.PDF

you haven't posted a link to the markscheme...

have you remembered the rules?
every time a ray comes to a boundary you take the normal to the boundary at that point and take angles from there... this may mean you're measuring/calculating angles relative to different directions at different points on the rays path.

θ is being measured relative to a horizontal normal
the critical angle 80 is being measured relative to a vertical normal

Reply 2

Hudl

OP

16

Original post by Joinedup

you haven't posted a link to the markscheme...

have you remembered the rules?
every time a ray comes to a boundary you take the normal to the boundary at that point and take angles from there... this may mean you're measuring/calculating angles relative to different directions at different points on the rays path.