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    (Original post by Music With Rocks)
    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
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    (Original post by ryandaniels2015)
    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
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    can someone help me understand the difference between single, double and diffraction grating please
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    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


    (Original post by Music With Rocks)
    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
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    (Original post by ryandaniels2015)
    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
    oooooohhh I was doing 24% thank you, that is great
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    (Original post by TSRPAV;[url="tel:65578851")
    65578851[/url]]You appling to uni/what course?
    Applying for physics at Lancaster....if I hadn't have blagged stats revision and got 55ums (yup) this year would be way less stressful....I'm basically either getting a b or a*.....m1 didn't help.

    Feel like all the exams are way more bunched up this year....I've got c3&4 physics 4 and bio 5 in the same weeks...gonna be fun

    What you applying for?
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    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.
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    (Original post by chrishannon09)
    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.
    i am thinking either interference patterns and formation of fringes or youngs modulus experiment

    do you have a model answer for a 6 marker on optical fibres?
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    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!
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    (Original post by chrishannon09)
    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
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    (Original post by Exams987)
    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
    What makes u think it might be that?
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    Ah that wouldn't be so bad, so roughly would be:
    - intensity of monochromatic (eg laser) greater than white light
    - monochromatic produces dots on screen, white light produces central white maximum then subsidiary maxima are spectra with blue closest to centre and red furthest (laser is coherent so wavelength/freq are constant so no spectra)
    - where waves are in antiphase there are dark fringes for both white and monochromatic light
    - laser light diverges very little compared to white light
    not sure what else. Thank you for the video, it was helpful!
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    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
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    (Original post by chrishannon09)
    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
    do you have a model answer for a finding wavelength of a laser light through diffraction grating or double slit.
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    Can anyone please help with JAN13 7e why if the wavelength goes 1/2 does it still form a maximum?
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    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)
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    (Original post by chrishannon09)
    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)
    thanks for your help
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    Anybody please!!
    (Original post by ryandaniels2015)
    can anyone please help with jan13 7e why if the wavelength goes 1/2 does it still form a maximum?
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    (Original post by ryandaniels2015)
    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
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    (Original post by chrishannon09)
    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
    Thanks for the reply, but where did u get 2n(X/2) From?
 
 
 
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