Interference and Diffraction

1. Interference and Diffraction

2. Two Pulses • What happens when two pulses of equal magnitude move towards each other on a string? • A) Bounce off each other as if there was a barrier. • B) Bounce off each other as if there was an open string. • C) Pass through each other like the pulse wasn’t there. • D) Pass through with some loss of amplitude. • E) Annihilate each other.

3. Superposition • When two or more waves are present at the same time they add together. • Includes different frequencies • Includes different wavenumbers • When waves are added at each point to form a new quantity, they are said to be in superposition.

4. As pulses reach the same spot they add directly. At later times they still add. When two waves make a larger wave they have constructive interference. Constructive Interference

5. Waves in the opposite direction can cancel each other out. The waves still separately exist and may be moving. This is called destructive interference. Destructive Interference

6. Ripples • Wave on the surface of water have both constructive and destructive interference. • Gaps where the ripples cross are from the destructive intereference.

7. Building a Square • Any wave form is the sum of harmonic waves. • One can construct a sequence of harmonic waves to match other shapes.

8. Small wavelength waves that encounter a large object leave a shadow area behind the object. Large wavelength waves that encounter an object leave less shadow area. This is called diffraction. Obstacles

9. When a wave reflects it sends the same frequency back again. There are two waves of the same frequency moving in opposite directions. This forms a standing wave. Standing Wave