Diffraction - Calculating Width of a Slit

[MRL]

Homework Statement

I am required to calculate the width of a single slit. I have known distance, L, between the observation screen and the slit, and photo images were taken of the resulting waveform. However, the wavelength is unknown, therefore making many of the equations I'm attempting to use void.

Homework Equations

asinθ = mλ ; for a dark fringe, were a is the slit width, λ is the wavelength, and m is the order of the minimum. However, as in my case both λ and a are unknown, this cannot be used.

The Attempt at a Solution

I'm usure as to what equations/theory i can use, although i know i can use pythagoras to find the distance between a fringe and the slit, using L and the distance of fringes from the centre of the screen.

Thanks.

 

[Dadface]

Hi MRL.Are you sure that the wavelength was not given,perhaps in a different part of the question or indirectly? Since you were given a photo image I'm assuming visible light was used so did the photo show what colour was used?If so you can look up the wavelength.If the photo was black and white you could give an approximate value for the wavelength eg the wavelength for yellow.

 

[MRL]

Hi MRL.Are you sure that the wavelength was not given,perhaps in a different part of the question or indirectly? Since you were given a photo image I'm assuming visible light was used so did the photo show what colour was used?If so you can look up the wavelength.If the photo was black and white you could give an approximate value for the wavelength eg the wavelength for yellow.

Thanks for the reply. It was practical experiment that i did, and we were required to take photos of the results. A red laser was used, so would you suggest i use the wavelength for red light?

 

[Dadface]

Yes,use the wavelength for red.I'm guessing it was a helium neon laser so you might want to google to get a more precise value for the wavelength.

 

[MRL]

Yes,use the wavelength for red.I'm guessing it was a helium neon laser so you might want to google to get a more precise value for the wavelength.

OK, thanks for your help.

 

[fluidistic]

Yes,use the wavelength for red.I'm guessing it was a helium neon laser so you might want to google to get a more precise value for the wavelength.

I second this tip. However...
It's always good to understand well the lab before proceeding. You could avoid to miss data (that aren't necessarily on the Internet).