# 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