View the diffraction pattern of a mercury lamp which emits a bluish color. The lamp will be used to calibrate the grating, i.e., to find the distance between adjacent slits, d and thus the number of lines per cm (1/d where d is in cm). Mercury emits three bright lines, a bluish-green line at 546 nm and two yellow lines at 577 nm and 579 nm. The two yellow lines are very close to each other and for the purpose of this exercise, they are treated as one line at 578 nm.

Measure the angles between the central maximum (blue line at 180A?°) and the bluish-green and yellow lines. (It does not matter whether you use the lines on the left or right of the central maximum for this exercise. However, for the lab, you will be asked to measure the angles on both sides since the spectrometer may not be properly aligned.) Then use the expression dsinθ=mλ to calculate the separation between adjacent slits, d. Do the same thing for the yellow line and then calculate the average of the two values and enter the value below.