PHYA5 ~ 20th June 2013 ~ A2 Physics

what are you all using to revise your optional topics?

I feel like I don't have enough resources for astrophysics

Collins aqa student support book for astrophysics, thats all you need then just do the past paper questions.

I just can't seem to be able to remember the lens stuff because it's SO boring! Any ideas on how to learn it?

what are you all using to revise your optional topics?

I feel like I don't have enough resources for astrophysics

Do you mean when it comes to drawing ray diagrams or the more detailed stuff such as resolving power and Rayleigh Criterion? I can help with you with both
.

Do you mean when it comes to drawing ray diagrams or the more detailed stuff such as resolving power and Rayleigh Criterion? I can help with you with both

Am I missing something because resolving power and Rayleigh criterion are not complicated from what I've read (just one formula and then like one line to memorise/learn for both)

I'm okay with the ray diagrams I believe, its just focal points when you're given the magnification and stuff, I never work out what exactly you're supposed to do Thanks!

Any more revision material on Turning points anyone?
Smith

Have you had a read through this?: http://filestore.aqa.org.uk/subjects/AQA-2450-W-TRB-OGTP.PDF

anyone got the collins student support book?

for astrophysics, (specifically binary star system), I'm having a real headache over this example question in the book on page 90:



Surely the tangental velocity (i.e the actual speed at which the stars are moving) would be different for each of the stars, so how can you get one single figure for velocity. I don't get this. They're each moving in their own orbits which are different sizes, and if the time taken (time period) to complete their respective orbits is the same, then surely the speed at which they're moving must be different....

secondly, why does that equation give you the distance between the two stars. Somehow it shows that 'r' (radius of 'circular motion) equals the distance between the two stars, It just doesn't make sense to me at all, how am I suppose to visualize this

You're correct, the tangential velocities of the two stars would be different, however because this is A Level Physics, we make assumptions and here we are assumuing that a smaller star is orbiting a bigger star, the bigger star acting as a centre of mass. Funnily, I was actually watching a lecture on binary star systems yesterday, take a look at the link below (Walter Lewin is a genius may I add).

http://ocw.mit.edu/courses/physics/8-01-physics-i-classical-mechanics-fall-1999/video-lectures/lecture-23/
Forward to 20:49

As for your second question, I think this is to do with the fact that you're assuming that you are in the same plane of the orbit of this binary system. Maybe these pictures may clear things up:



If you look at the second picture, the radius of orbit of the smaller star is the same as the distance between both stars.

Hope I've helped you!

Thanks

So in that example question I posted, one of the star is basically not moving? and this is the reason why we would get only one tangential velocity?

I've looked at the animation you provided, is that suppose to represent my example question?