Phase difference Flashcards
What is superposition?
Superposition: total displacement due to several waves is sum of displacement of waves individually.
What are dead spots?
Some concert halls have acoustic dead spots where volume is lower than expected. Sound waves reflected from the walls and ceiling superpose causing the amplitude of the wave to reduce.
How can teachers become quieter when speaking?
If a teacher speaks at the right frequency there are places where amplitude is reduced as sound waves superpose.
What happens when you walk between two speakers, find a quiet spot, and the speaker is turned off?
Walking between two loud speakers, if you walk to a sound which is quiet and a speaker is turned off, volume increases again.
What is interference?
Interference describes the pattern of superposition, an alternation of loud and quiet positions. Where waves meet in phase, sound is loud. In antiphase, sound is quiet. If the waves have equal amplitude, they will cancel completely.
Where on a standing wave are points in antiphase?
Between two adjacent nodes, points are in antiphase with the node before those two.
If paper is placed on a standing wave, at which point will it not fall?
A node.
What are conditions for path difference and superposition?
When path difference is n wavelengths, the waves meet in phase and superpose producing a superposition maxima. If the path differences are n+1/2 wavelengths, the waves will meet in antiphase and produce superposition minimum.
What’s coherence?
A stable superposition pattern is one where the maxima and minima don’t change over time unless the speaker is moved or frequency changed. Stable superposition patterns only occur where there’s constant phase difference between waves - they’re coherent.
How do noise cancelling headphones work?
Some background noise is blocked by the material of headphones, reducing energy of sound waves.
Noise reducing headphones use microphones which detect background noise. Electric circuitry flips the waveform so it is in antiphase with background noise, and is fed into the headphone speakers.
How can wavelength be found using microwaves and a mirror?
A microwave transmitter is set up with a receiver at one end and a mirror above. Moving the mirror will change whether maxima or minima are detected. Measure the path difference for the first maxima, and then path difference for the second minima to determine wavelength.
