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phys doubt
halosh92:
--- Quote from: Phosu on March 27, 2010, 12:53:34 pm ---The interference patterns from a diffraction grating and a double slit are compared.
Using the diffraction grating, yellow light of the first order is seen at 30° to the normal to the
grating.
The same light produces interference fringes on a screen 1.0 m from the double slit. The slit
separation is 500 times greater than the line spacing of the grating.
What is the fringe separation on the screen?
A 2.5 × 10^–7m
B 1.0 × 10^–5m
C 1.0 × 10^–3m
D 1.0 × 10^–1m
plz show how to solve,
i know the two formulas, but i dont know how to use them
--- End quote ---
is it C?
astarmathsandphysics:
When I get home
Phosu:
--- Quote from: halosh92 on March 27, 2010, 01:06:08 pm ---is it C?
--- End quote ---
yah, how did you find it out?
halosh92:
--- Quote from: Phosu on March 27, 2010, 03:13:53 pm ---yah, how did you find it out?
--- End quote ---
ok so first we have these 2 formulas:
d sin thita= n (lambda) equ 1
(lambda) = ax/D equ 2
the information we got for equation one is :
thita=30
n=1 (first order as mentioned)
d= unknown
wavelength of yellow light approximately = 500nm
the information we got for equ 2 is:
D=1 m
a = 500 d ( as they say its 500 times)
therefore substitute values in equ 1 :
d sin thita= n lambda
rearrange
d= (1 * (500 *10^-9) )/ sin 30 >>>>> (mind u we multiply 500nm * 10^-9 to change it to "m" )
d= 1 * 10^-6 m
now substitute in equ 2 :
lambda= ax/D
rearrange
lambda/aD =x
now substitue values:
( 500 * 10^-9)/(500 * (1*10^-6) *1)
answer:
1 *10^-3 which is C
Phosu:
Thanks so much for the explanation
a few doubts, do we need to know the wavelength of each light?
i know n stands for the order, but what does "d" stand for?
and you got the last rearrangement rong,
if (lambda)= ax/D
then (lambda)D/a=x
in this case since D is equal to 1, it wouldn't affect the answer. but in other cases be careful.
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