yah, how did you find it out?
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