Unit 11
Waves and sound.
What a wave carries: wavelength and frequency, sound, interference, standing waves, and the Doppler effect.
Before this unit
The unit, lesson by lesson
Lessons
5 lessons · 25 practice questions · about 2 hours
Wavelength, frequency and speed
What a wave carries and what stays in place, and three numbers that describe it: the frequency the source sets, the speed the medium sets, and the wavelength that fits both.
Sound
Sound is a longitudinal wave of compressions and rarefactions: its wavelength in air, what loudness changes and what it doesn't, what happens when sound passes into water, and echoes.
Interference
Two waves that meet add up: constructive and destructive interference, the path difference that decides where the water is calm, and how many calm lines fit between two sources.
Standing waves
A wave reflected back and forth between two ends settles into a pattern that does not travel: nodes and antinodes, the wavelength of each harmonic, the frequencies of the harmonics, and how a string's length sets its pitch.
The Doppler effect
A moving source squeezes the waves in front of it and stretches them behind: the wavelength and frequency ahead of the source and behind it, why a passing siren drops in pitch, and what happens at the wave speed.