![]() These are maximum and minimum wavelengths which are indicated on the lasers themselves, so I knew approximately what the wavelength should be to see if I got the right answer. In the table you can see two rows (min and max). I repeated this experiment for this instructable to produce the graph above. Wavelength is usually expressed nano meters (10^-9 m) so you will need to consider if you want to convert your answer to nano-meters or simply express is a something times 10^-9. Remember that all these distances are in meters. Together with x and d we can now calculate wavelength. ![]() If we divide 1m by 500,000 lines, we get the distance between them which is 2 µm. Well, if we know the grating has 500 'lines' per mm, that means there are 500,000 lines per m. All of this is available for you to substitute into the equation to give you the wavelength.īut you might ask "how do I know what 'a' is?". This is because I did this a few times to determine uncertainty in the measurement).īut how does this relate to wavelength? The equation is lambda = (a * x) / d, where 'lambda' is the wavelength in meters, 'a' is the distance between the slits in the diffraction grating, 'x' is the fringe separation, and 'd' is the distance between the screen and the grating. (You'll notice that there is a discrepancy between the picture and what I have recorded in my results later. Once you have done this for all lasers, measure the distance between the middle fringe and the 1st fringe next to it (this is known as the 1st order fringe).Repeat step 1 for each colour, marking the fringes on the paper.Make sure you write down the middle one and the ones on both sides. When the lasers hit the paper (screen) write down with a pen where the light spots occur (these are known as finges).To find the wavelength of the laser you need to measure the fringe separation. ![]()
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