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# (Help!) AS Physics - Diffraction Grating question watch

1. I know that I'm asking for a lot, but I'm kind of stuck on this and I don't know how to work this out (I'm probably confused because of the wording of the question?)

a) A grating has 100 lines per mm and when displayed on a screen 2.0 m away, the 3rd maximum is 33cm from the centre.
i) what is the separation of the centres of the slits.
ii) What is the angle that this maximum makes with the centre line?
iii) What is the wavelength of the laser?

I would really appreciate it if someone was to explain to me how to work out the question. Thank you <3
3. n = d sin( )
I did edexcel so never had to answer that kind of question but i'll do my best to help anyway!
as you can see from the equation above, it relates all the things you need to know. n is the order (in this case 3), lambda is the wavelength, d is the distance between slits(here it would be 100/1x10-4) and theta is the angle!
as you have the length of the screen from the light, you can set up a triangle where the adjacent side to theta is 2m, the opposite is 0.33 and then use some trig(tan^-1(0.33/2)) to find theta! tbh i dont really understand what the first part is asking but you can work out ii) im pretty sure, and also iii) using the equation
hope this helped!
4. (Original post by Jozden)
n = d sin( )
I did edexcel so never had to answer that kind of question but i'll do my best to help anyway!
as you can see from the equation above, it relates all the things you need to know. n is the order (in this case 3), lambda is the wavelength, d is the distance between slits(here it would be 100/1x10-4) and theta is the angle!
as you have the length of the screen from the light, you can set up a triangle where the adjacent side to theta is 2m, the opposite is 0.33 and then use some trig(tan^-1(0.33/2)) to find theta! tbh i dont really understand what the first part is asking but you can work out ii) im pretty sure, and also iii) using the equation
hope this helped!
Thanks so much for the helping me out there /hugs
The exam board I am taking for A-Levels is the WJEC exam board.

I don't know if I got it right but I got the answers for:
ii) 9.37 degrees (3sf)
iii) 5.43*10^-7 m

I am very confused about the first part of the question. What does it even mean by what the separation of the centres of the slits?
5. (Original post by minibuttons)
Thanks so much for the helping me out there /hugs
The exam board I am taking for A-Levels is the WJEC exam board.

I don't know if I got it right but I got the answers for:
ii) 9.37 degrees (3sf)
iii) 5.43*10^-7 m

I am very confused about the first part of the question. What does it even mean by what the separation of the centres of the slits?
To clarify, the seperation of the centres of the slits means in this context (as the slits are very narrow) how far the slits are from each other.

(HINT there are 100 per mm )
6. (Original post by natninja)
To clarify, the seperation of the centres of the slits means in this context (as the slits are very narrow) how far the slits are from each other.

(HINT there are 100 per mm )
is it 1 mm? shdfjdshj I don't know OTL
7. (Original post by minibuttons)
is it 1 mm? shdfjdshj I don't know OTL
er... no...

there are 100 slits per millimeter so it would be 1mm divided by 100.

(Assuming that is what the question is asking for...)
8. (Original post by natninja)
er... no...

there are 100 slits per millimeter so it would be 1mm divided by 100.

(Assuming that is what the question is asking for...)
So would it be: d = 1/100*10^3 ?? (I'm trying to convert it to metres).
9. (Original post by minibuttons)
So would it be: d = 1/100*10^3 ?? (I'm trying to convert it to metres).
looks about right, should be a small number
10. (Original post by natninja)
looks about right, should be a small number
ok so d = 1/100*10^3 = 1.0*10^-5 (also what would the units be if there are any?)
Also thank you for helping me out there Would my other answers me right then for ii) and iii)?
11. (Original post by minibuttons)
ok so d = 1/100*10^3 = 1.0*10^-5 (also what would the units be if there are any?)
Also thank you for helping me out there Would my other answers me right then for ii) and iii)?
Yes should be

well 'n' would be 3 and you just worked out 'd' for the formula that someone gave earlier I believe.

I'm afraid I don't have a calculator at hand but they sound like they could be right. just check with that number you just worked out

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