Young’s double slit experiment and diffraction grating.
Equipment:
Laser
Single slit
Double slit
Diffraction grating
Metre ruler
Vernier callipers
Retort stand
White screen (e.g. mini whiteboard).
Aim of experiment – investigate relationship between the slits and the screen with the fringe width. w = ƛD /s.
Independent variable – fringe width, w
Dependent variable – distance between the slits and the screen, D.
Control variables:
Laser Wavelength, λ
Slit separation, s.
Instructions:
Fix laser and the slits to a retort stand and place the screen so that the D is 0.5 m, measured using the metre
ruler.
Turn off room lights and turn off laser. Make sure the laser is only facing whiteboard as if it reflects of
something or goes through a window, it could cause damage to someone’s eye.
Use a pen to mark where on the whiteboard the central fringe and the fifth fringe to either side.
Turn of the laser and turn the lights on and measure the distance between the two lines on your whiteboard
using a vernier calliper.
To find the fringe width, w, divide the measurement by 5.
Increase the distance by 0.1m m and repeat the procedure, increasing it by 10 cm each time until it reaches 1.5
m.
Repeat the experiment twice again and then calculate and record the mean fringe width, w for each distance
D.
D / m W / m 1st reading W / m 2nd reading W/m 3rd reading. W/mean
0.5
0.6
9.7
0.8
0.9
1.5
1.6
1.7 0.0052 0.0052 0.48
1.8 0.0064 0.0064 0.0064
1.9 0.008 0.008 0.008
2 0.009m 0.009m 0.0084
