6.2.5.3 Interference of Light Wave

Young’s Double Slits Experiment

1. Young's double-slit is made up of two slits ruled on a piece of slide and painted with 'aquadak'.
2. When monochromatic light passes through the Young's double-slit, diffraction of light occurs and two coherent sources (same amplitude, frequency and phase) are produced.
3. The two coherent sources will overlap and superpose to produce the effects of constructive and destructive interference.
4. Constructive interference generates bright fringes while destructive interference produces dark fringes.
5. Fringe size of bright fringes and dark fringes are about similar in size.
6. Requirement for the interference pattern to be observable:
   1. Monochromatic light is used
   2. The size of the slit need to be very small
   3. The distance between the 2 slits must be small (About 0.5mm)
7. The distance between fringes increase as
   1. light with longer wavelength is used
   2. the 2 slits is closer
   3. the distance between the double slit and the translucent screen is increased.
8. The wave length of light wave can be calculated by using the following equation: $$\lambda =\frac{ax}{D}$$

Compare to the pattern of single slit experiment

Young's Double Slits Experiment (Interference)

Single Slit Experiment (Diffraction)