Young’s Double Slit Experiment. Today’s agenda: Review of Waves. You are expected to recall facts about waves from Physics 1135. Young’s Double Slit Experiment. You must understand how the double slit experiment produces an interference pattern. Conditions for Interference in the Double Slit Experiment. You must be able to calculate the conditions for constructive and destructive interference in the double slit experiment. Intensity in the Double Slit Experiment. You must be able to calculate intensities in the double slit experiment.

Interference Review of Waves This section is a review of material you learned in your previous physics course (probably Physics 1135). y Consider a wave described by x The phase of this wave is Also, the phase changes with time:

If the wave is moving from left to right then /k must be positive. If  is constant with time (i.e., d/dt=0), then we are moving with the wave, and The phase velocity, vp, is given by y Imagine yourself riding on any point on this wave. The point you are riding moves to the right. The velocity it moves at is vp. x If the wave is moving from left to right then /k must be positive.

Superposition—a Characteristic of All Waves When waves of the same nature travel past some point at the same time, the amplitude at that point is the sum of the amplitudes of all the waves The amplitude of the electric field at a point is found by adding the instantaneous amplitudes, including the phase, of all electric waves at that point. In Physics 1135 you may have learned that power (or intensity) is proportional to amplitude squared. The intensity of the superposed waves is proportional to the square of the amplitude of the resulting sum of waves.

Interference—a Result of the Superposition of Waves Constructive Interference: If the waves are in phase, they reinforce to produce a wave of greater amplitude. Destructive Interference: If the waves are out of phase, they reinforce to produce a wave of reduced amplitude.