Physlet Illustration: Double-Slit Interference

 

 
l = mm d = mm
In this simulation, waves in a ripple tank originate from two small slits, shown in red. You may vary both the wavelength and the slit separation. The resulting interference may be observed in the ripples of the waves that propagate in the tank. Angles at which totally constructive interference occurs are characterized by alternating peak and troughs. Angles at which totally destructive interference occurs are characterized by an absence of such "ripples". At what angles do these interference phenomena occur?

Hints:

  1. Change the slit separation. (0.1 mm < d < 2 mm) How does it affect the interference pattern?
  2. Change the wavelength. (0.5 mm < l < 5 mm) How does it affect the interference pattern?
  3. Verify that there is always constructive interference at q = 0° (straight up).
  4. Constructive interference also occurs at angles where the waves from the two slits are in phase. What is the condition for this to occur?
  5. Destructive interference occurs at angles where the waves from the two slits are out of phase by 180°. What is the condition for this to occur?

Reference

See Walker, Section 28-2

Illustration written by Steve Mellema