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# The Physics PHYA2 thread! 5th June 2013 watch

• View Poll Results: What mark do you think you got out of 70?
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1. (Original post by Emma1124)
Does anyone have a few steps that can help me when working a question says to show the path of the ray until it returns to air, the seem to always get me! Thanks!!
think of the light ray as a car, and when it refracts going into a denser medium, the side of the car that hits the boundary first slows down first, allowing the other side to catch up, so the light bends towards the normal and vice versa
2. question 4 b i) on the june 2012 paper? thanks so much!!
3. (Original post by frankieeeeeee)
question 4 b i) on the june 2012 paper? thanks so much!!
Q4ai right? Since the angle is 85 degrees to the left, it is also 85 degrees inside the ray that forms the triangle. (Note: The angle of reflection is always the same as angle of incident). So, to find i, you add 85 + 30 which gives 115 degrees. Since triangle is 180, 180 - 115 gives 65 degrees. Any more help? Ask me
4. (Original post by StalkeR47)
Alright! How confident are you feeling for the physics exam?
Mmmm, not too sure. I know the content pretty well but I always have the feeling they're gonna ask something which I'll struggle to do. Otherwise, I'm pretty confident I guess.
5. when do you use f cos theta or f sin theta its confusing me some say horizontal or vertical others say line of action
6. (Original post by StalkeR47)
Q4ai right? Since the angle is 85 degrees to the left, it is also 85 degrees inside the ray that forms the triangle. (Note: The angle of reflection is always the same as angle of incident). So, to find i, you add 85 + 30 which gives 115 degrees. Since triangle is 180, 180 - 115 gives 65 degrees. Any more help? Ask me

thanks so much!
i wasn't sure you could use 85 as the angle inside the triangle!
good luck for tomorrow
7. (Original post by dark3city)
when do you use f cos theta or f sin theta its confusing me some say horizontal or vertical others say line of action
On the inclined, well.... Someone have already drawn a nice diagram.
8. Is there an easy way to calculate work done on a Load/extension graph? There's a question for this on June 10 5b which I can't do.
Thanks!
9. (Original post by dark3city)
when do you use f cos theta or f sin theta its confusing me some say horizontal or vertical others say line of action
Here!

10. the ms says 1.4 my calc gives 0.6 -.-
11. (Original post by StalkeR47)
Jan 13 last q? Common! It was the easiest question. But you are doing really well! Keep it up!
I know aha! Just didn't like it :')

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12. (Original post by frankieeeeeee)
thanks so much!
i wasn't sure you could use 85 as the angle inside the triangle!
good luck for tomorrow
no probs! Good luck to you too for tomorrow! You will be fine!
13. (Original post by RU486)
Is there an easy way to calculate work done on a Load/extension graph? There's a question for this on June 10 5b which I can't do.
Thanks!
Area under the graph
14. (Original post by RU486)
Is there an easy way to calculate work done on a Load/extension graph? There's a question for this on June 10 5b which I can't do.
Thanks!
The area is wd. Count the number of blocks and times the number of blocks by the area of each block.

Question 6di from June 2010!

I'd truly appreciate it
16. (Original post by frankieeeeeee)
Can anyone explain Q. 4. b) (i) from the June 2012 paper?
It's on fibre optics and I really don't understand, the fibre is bent at 30 degrees and it asks you to calculate the angle of incidence.

What?

Thank you.

The laser beam at first undergoes total internal reflection, so this angle is also 85 degrees, thus i=180-85-30=65 degrees.

Let be the cladding and be the core, and applying snell's law:

$\frac{1.41}{1.46}= \frac{ \sin(i)}{ \sin ( r )}$
$\sin ( r)= \frac{1.46}{1.41} \sin(i)$
$r= \sin^{-1}( \frac{1.46}{1.41} \sin(65))=69.79$ degrees.

(Edit: see
http://latex.codecogs.com/gif.latex?...sin(65))=69.79 for the [latex] bits, TSR's latex is buggy)

17. hi guys can some one please upload the MS AND QP jan 2013 unit 2 pleaseeeeeeeeeeeeeeeeeeeeeeeeeee eeeeeeee

my stupid teacher forgot to email
18. (Original post by Sukura)

Question 6di from June 2010!

I'd truly appreciate it

6(d)(i) is simply 1/d, where d is the slits per mm. Although, be VERY careful with your s.f and standard form here. Mark scheme suggests that an incorrect s.f is no mark.
19. (Original post by BenChard)

the ms says 1.4 my calc gives 0.6 -.-
Which exam paper and which q?
20. (Original post by BigBadJFly)
Area under the graph
(Original post by StalkeR47)
The area is wd. Count the number of blocks and times the number of blocks by the area of each block.
Ah okay, thanks

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