I fired a laser through a diffraction grating which turned a single laser dot into 14 dots (fringes). The central fringe is n=0. There is a first order (n=1) on either side etc. I've labelled some of them on the photograph below.
Your job is going to be to measure the distance for each order from one side of the centre across to the other side. I have shown below for n=1 and I am going to call that distance y1. You will then be asked to HALVE it to get x1. The reason for measuring twice the distance that we actually need is that it halves the percentage uncertainty in the reading.
I also measured the distance D from the fringes to the grating.
Here is the reading for D.
On the photograph below, x1 is half of the measurement y1 made above. When you have found x1 and D, you calculate angle theta by using trigonometry as shown below. Eventually you will be calculating sin(theta)
The next set of photographs will allow you to make measurements for y1, y2, y3, y4, y5, y6 and y7. Make a table with columns for n, y, x, theta and sin(theta)
I used the 100 lines per mm grating. Remember that in the equation n.lambda = d.sin(theta), d is the slit separation. d is NOT the same as lines per mm. There are 100 lines in 1mm. You can then calculate how far apart 2 lines are. That is d.
In the end, you plot a graph of n on the y-axis against sin(theta) on the x-axis. The graph should be a straight line through the origin. Gradient = d/lambda so you can use the gradient to calculate a value for the wavelength of this red laser light.
