AQA AS Physics Unit 2 (PHYA2) June 9th 2016 Resit paper

Yeah but you need the strain first, it is the first part of the working if you look at the mark scheme above

Oh yes sorry basically:

YM = STRESS/STRAIN

Rearrange

YM * STRAIN = STRESS

2.8X10^11 * CHANGE IN L/L = STRESS

Change in L = 1.5*0.24/100
= 3.6*10-3

therefore

2.8x10^11 * 3.6*10-3/1.5 = 6.7X10^8

why is it"Change in L = 1.5*0.24/100
= 3.6*10-3"?

Surely L is the original length which is 1.5 and L changes by 0.24 so 0.24/1.5? :P

sorry I don't quite get it

L has original length 1.5. it increases by 0.24% which is equal to 0.24/100

e.g.

if I have an object 10m in length and increases by 10% is
10*10/100 = 1m

so it increases by 1m
therefore new length is 11m

but extension is 1m

doing some last minute revision, what does everyone think the 6 marker will be on if anyone's up? Saw someone said it could be about optical fibres, what would be a possible question be like on that topic? vaguely of course.

Young's Modulus would be a dream, interference patterns not so much. no i don't i apologise, i'm not even sure what they would ask for 6 marks on optical fibres - perhaps a general question tying in aspects like reasons for cladding, reasons that multipath dispersion occur etc? Honestly have no idea. What would a 6 marker on interference patterns look like if you have an idea? I suck at them so any possible question to expand my knowledge would be great!

i really hope it is on youngs modulus.

a possible 6 marker could be

comparing white light and monochromatic

watch this video https://www.youtube.com/watch?v=MnbpDx1tvaQ

the 6 markers that i can remember have been on stationary waves, young's modulus, finding spring constant, finding wavelength of a laser light through diffraction grating or double slit, and newton's laws. I was thinking they might do a question on polarisation but can't think of any 6 markers they could ask for that - that would be killer, I can remember barely anything on it

diffraction grating:
-find distance from screen to grating (D). Use large value of D (>2m), repeat for different values of D for accuracy
-measure dist between first order maximum + sub maxima (x), repeat between different order maxima
-find angle theta between them using tan theta = x/D
-find d by calculating 1/lines per mm of grating. If lines per m is given, use (1/lines per m) x10^3
-use wavelength = d sin theta to find wavelength
for double slit:
-find dist between slit + screen (D) with meter rule, measure fringe separation (w) between centre of fringes with vernier scale
-use 7+ values of w, repeat 2x and calculate mean value
-use wavelength = ws/D (s=slit separation) to find wavelength
-use large value of D (maybe repeat for different values of D)

can anyone please help with jan13 7e why if the wavelength goes 1/2 does it still form a maximum?

Can anyone please help with JAN13 7e why if the wavelength goes 1/2 does it still form a maximum?

sorry don't have lambda symbol so gonna use X
if previous wavelength is X then path difference was nX as a maximum was seen. if new wavelength is X/2, path difference is still nX (i believe?) which is the same as 2n(X/2) - this is an even number so waves are in phase and so maximum is seen