Why is our diffraction grating producing incredibly inaccurate angles of diffraction?

Question

Our grating is from a Frey Scientific cat.no.17912, and the package says they have 500 lines/mm. For some reason, from the angle that we are getting by shining a red laser pointer through, we are calculating the wavelength of red light to be almost twice as much as it should be. What's going on?

Answer 1

From dim recollection of Physics Lab Work you must rotate the grating until you get maximum deflection. This is best done on a properly constructed Spectrometer which I think is geared 2 to 1. I seem to remember this made the incidence angle and refracted angles equal.
If you do this you should get the correct answer but I would imagine it is tedious work without the Spectrometer!

Answer 2

Hey thanks for the Canadian compliment.... Actually, I have a visual for you - since I'm not mathematical. In my city, there is a very busy expressway that cuts the city in half. They actually tore down neighbourhoods to build it in the 70's. In the 80's, they found the money to build the sound barriers for the benefit of the people who are still living next to it. In this one section, which I drive by frequently, the houses are about 80 feet or so from the wall, with the expressway butt up against it on the other side. The expressway is 6 lanes at that point. The wall is at least 16 feet high. If I get out of my car at that point, I can barely hear the traffic on the other side. Conversely, (and I don't understand this), my mother lives very near the expressway. She has a very deep lot with city owned property behind that. It's all dense bush which you would think would be somewhat of a barrier, but no. If the wind is in the right direction, you practically have to yell when you are in her backyard to be heard. :))) (((((uunnccllee) - please be careful when building your wall.....

Answer 3

ITS CALLED A MIRROR