Light interference homework

1. Jun 9, 2006

sssddd

the question is A plane wave of 400-nm light is incident on a 25-µm slit in a screen, as shown in the figure below. At what incident angle will the first null of the diffraction pattern be on a line perpendicular to the screen?

2. Jun 9, 2006

Hootenanny

Staff Emeritus
Well, do you know the condition / formula for single slit interfence?

3. Jun 9, 2006

sssddd

it's the one with the sin theta right or something right? please point me to the right track

4. Jun 9, 2006

Hootenanny

Staff Emeritus
I think this can be solved using the Fraunhofer Single Slit Diffraction relationship;

$$a\sin\theta = m\lambda$$

Where a is the size of the slit, $\lambda$ is the wavelength and m is the order of the minima.

5. Jun 9, 2006

sssddd

ok ok i think i am remembering this now, and m would be 1 right for first null. when they say null they mean the minima fully destructive right

6. Jun 9, 2006

Hootenanny

Staff Emeritus
I am assuming that's what null means a minima (I haven't heard that terminology for a while). Yes, the fist minima would be at m = 1. This is different to maximas where the first maxima is at n = 1.

7. Jun 9, 2006

sssddd

ok thank you so much now i can find the angle easily

8. Jun 9, 2006

Hootenanny

Staff Emeritus