A screen with three slits and 1 gets blocked --> diffraction?

[ElectricEel1]

Homework Statement

A screen with three equally spaced slits of the width b and separation a is illuminated at normal incidence with monochromatic light with wavelength lambda. A diffraction pattern is obtained at a distance L on another screen positioned behind the screen with the slits. Calculate and compare the distance between the diffraction maxima with numbers m and m+1 for the cases when either the middle or one of the side slits is blocked. Assume a>>m*lambda

Homework Equations

a*sin(theta)=m*lambda
Y=(m*lambda*L)/a

The Attempt at a Solution

Im not entirely sure what it is asking me to do but I started by finding the equations I wanted to use then figured the separation for blocking the middle would be 2a+b and the separation for blocking one of the side slits would just be a.

Then I wrote the two cases up and took the difference between the Y at m=2 and m=1 for both. With no values given I'm not sure where to go next just with algebra, I subbed in some values of
a=300 micron b = 10micron L = 10m lambda = 500nm
and got 0.0082m distance in the first case and 0.017m in the second case but I am not sure this is what I'm being asked to do.

Thanks

 

[BvU]

separation for blocking the middle would be 2a+b

That's not logical if you use a for the side slit blocked case. Usually separation a means from center to center.
Otherwise Ithink you are doing fine. Check with Hyperphysics if in doubt

 

[ElectricEel1]

That's not logical if you use a for the side slit blocked case. Usually separation a means from center to center.
Otherwise Ithink you are doing fine. Check with Hyperphysics if in doubt

its just 2a, right? not 2a+b for when the middle slit closes. that way everything should scale and the y position of the middle slit blocking will be half

 

[BvU]

piece of cake. looks good to me