# Young's Double Slit Experiment lab

1. Jan 19, 2014

### braeden

In class we did a lab regarding the wave nature of light. We pretty much conducted Young's double slit experiment. For the lab we were supposed to establish the relationship between the distance from the slits to the viewing screen and the distance between successive maxima. Can anyone explain to me, physics wise, why as the distance between the viewing screen the distance between successive maxima increases proportionally as well. I can obviously figure it looking at the formula but need a explanation of what's going on for my lab. Thanks

2. Jan 19, 2014

### ZapperZ

Staff Emeritus
Er... this is straightforward trigonometry.

These maxima and minima are at particular angles. So if you look at the first maximum, it comes out of the slit at a fixed angle. So if you consider A as the distance to the screen and O is the distance to the first maximum, then if you keep the angle $\theta$ fixed, can't you see that O will get larger as A increases?

Your a trig. function (I'll let you figure this out yourself which one is relevant) to relate the angle, distance A, and distance O, you should be able to get the exact relationship between all three.

In the future, please write down exactly the mathematical description that you know, and start from there.

Zz.

3. Jan 19, 2014

### jostpuur

It almost appears as if you are trying to make the original question sound as dumb. I wouldn't approve of that, because it is not obvious at all why the maxima and minima would come at particular angels. They do so only as an approximation when the distance between the slits is signifigantly smaller than the other distances in the situation. In order to prove this nicely, one of the most obvious ways (IMO) is to apply the approximation

$$\sqrt{1 + x} \approx 1 + \frac{x}{2}$$

So that's the level of math that is required for this.

4. Jan 19, 2014

### ZapperZ

Staff Emeritus
Er... no. I was pointing out the nature of the problem. Indicating that this is probably a math question might provide the OP a place to look. Furthermore, the OP indicated that he/she has the mathematical "formula" to look at. Knowing exactly what it is is the starting point since that is something the OP knows.

My philosophy in teaching has ALWAYS been to start where the understanding stops!

Do you really think that, at this level, this is not a far-field situation? Near-field 2-slit experiment is highly unusual. Based on the description given in the OP, I see this as being a standard, straightforward 2-slit experiment in an intro lab. Do you see otherwise?

Zz.

5. Jan 20, 2014

### jostpuur

I believe the original problem was a far-field situation. I also believe that braeden has had difficulty understanding what it means.