Double Slit Experiment

Question 1

What equipment is used in this experiment?

Answer 1

• Laser
  -Double Slit
  -White Screen
  -Metre Ruler

Question 2

What is Method?

Answer 2

-Ensuring that the laboratory is partially darkened, set up the apparatus as shown in the diagram.

-Adjust the apparatus so that D is 0.5m, measured using the metre ruler.

-Measure across a large number of fringes using the ruler and divide by the number of fringe widths to find the fringe width w.

-Increase D by 0.1m and repeat this, increasing it by 0.1m each time up to 1.5m.

-Repeat the experiment twice more and find and record the mean w for each D

-if it is not quoted on the double slit, the slit separation must be measured using a vernier calliper or a travelling microscope

Question 3

What graphs and calculations?

Answer 3

Plot a graph of w against D and draw a line of best fit. The wavelength of the laser light will be the gradient multiplied by the slit separation.

w =λD/ s ⇒ λ = ws/ D = G where G is the gradient.

Question 4

What safety precautions could we use?

Answer 4

• Proper signage to state that a laser is being used
• point laser downwards to avoid eye contact

Question 5

What improvement can be made?

Answer 5

Make sure that the screen and double slit are aligned perfectly normal to the laser to avoid parallax error in the measurement of the fringe width. A set square can be used in conjunction with the ruler.