# Wave Properties 2

• Created by: JC:8-9-9
• Created on: 24-12-18 09:40
• Wave Properties 2
• Principle of superposition
• When 2 waves meet, total displacement at a point is equal to sum of individual displacements at that point.
• Crest meets crest, super crest created.- 2 waves reinforce each other.
• Trough meets trough, supertrough created- 2 waves reinforce each other.
• Crest meets trough of same amplitude- cancel out- 0 resultant displacement. Not same amplitude - resultant- minimum.
• Examples
• Stationary waves on rope
• 2 people send waves from either end, 2 sets of waves - -progressive waves. Combine at fixed points along rope- nodes - no displacement. At node, 180 degrees out of phase, cancel out.
• Water waves in a ripple tank
• Vibrating dipper on water surface sends circular waves. Cancelling points - crest from 1 dipper meets trough from other.- gaps in wavefronts.
• Points of reinforcement- crest/trough from one dipper meets crest/trough from other
• Constant phase frequency at constant phase difference, cancel and reinforce at fixed positions- Interference. Coherent sources.
• Phase difference changed at random, points of cancel and reinforce- move at random, no interference seen.
• Tests for Microwaves
• 1. Place receiver in path of microwae beam from transmitter. Move away from transmitter and note receiver signal decreases with distance. Microwaves weaker travel away from transmitter.
• 2. Place metal plate between transmitter and receiver- can't pass through metal.
• Transmitter produces microwaves of 3cm wavelength. Receiver connected to meter, measure of intensity of microwaves at receiver.
• 3. 2 Metal plates - make narrow slit - receiver detects waves diffracted as pass through slit. Wider - less diffraction.
• 4. Narrow metal plate with 2 plates from step 3. - make pair of slits. Direct transmitter at slits and use receiver to find points of cancellation and reinforcement where microwaves from 2 slits overlap.

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