CB Chapter 6 Waves and sounds Flashcards
What is a wave?
Oscillations or vibrations about a rest position. The oscillations have a direction whilst the wave itself also has a direction.
What do waves transfer and what do they not transfer?
Waves transfer energy across locations but do not transfer matter
What are the main types of waves?
Transverse waves and longitudinal waves
What are oscillations in waves?
The to-and-fro movement of parts of the medium (EG: a slinky’s coils moving back-and-forth)
What is a transverse wave?
A wave where the oscillations are at rights angles to the direction of travel (EG: a slinky’s coils moving up and down whilst the wave moves to the right)
What are two important features of a longitudinal wave?
Compressions and rarefactions
What is a longitudinal wave?
A wave where the oscillations are in the same direction as the direction of travel (EG: a slinky’s coils being compressed and stretched out as the wave moves to the right)
What is a compression?
A section where the medium is more compressed (EG: part of a slinky’s coils being compressed together due to a longitudinal wave)
What is a rarefaction?
A section where the medium is more stretched out (EG: part of a slinky’s coils being stretched out due to a longitudinal wave)
What are examples of transverse waves?
electromagnetic waves: radio waves, microwaves, infrared, light, ultraviolet, X-rays, gamma rays
What is an example of a longitudinal wave?
sound waves
Are seismic waves transverse or longitudinal?
P (primary) waves, able to travel massive distances through the Earth, are longitudinal. S (secondary) waves, which are slower, are transverse
What happens when you speak?
compressions and rarefactions travel through the air
What is the speed of a wave?
The speed at which the wave moves. Its SI unit is m/s
What is the frequency of a wave?
The number of waves passing any point per second. Its SI unit is hertz (Hz). 1 Hz = 1 oscillation / second
What is the period of a wave?
The time needed for one full oscillation. Its SI unit is seconds (s).
What equation links period and frequency?
period (s) = 1/frequency (Hz)
What is the wavelength?
The distance between any point on a wave and its equivalent point on the next wave. Its SI unit is metres (m)
What is the amplitude?
The maximum distance a point moves from its rest position when a wave passes. Its SI unit is metres(m)
What is the wave equation?
speed (m/s) = frequency (Hz) * wavelength (m)
What is the wave equation in symbols?
(Imagine this in your mind and remember the symbols)
v = fλ
λ is the Greek letter lambda
Why does the wave equation work?
EG: assume λ = 2 m. There is a flag, and after 1 second, 3 waves have passed the flag. The frequency is 3 Hz. The waves have moved 3 wavelengths in 1 second. 3 Hz (frequency) * 2 m (wavelength) = 6 m/s (speed)
What is a ripple tank?
A transparent, shallow tray of water with a light shining downwards through it onto a screen below. The ripples are preferably produced by a motor
See an image
What is reflection?
Reflection is when waves hit a surface and travel in a new direction away from the surface
How does reflection occur?
The waves are reflected from the surface at the same angle they hit it
What can happen when waves slow down, what is this called?
The waves can change direction. This is called refraction
What is diffraction?
The process of waves bending around the sides of obstacles and spreading out as they pass through gaps
When is diffraction significant?
When the size of a gap is about the same as the wavelength
How does a wider gap affect diffraction?
A wider gap produces less diffraction
What are some real-world examples of reflection?
Light reflects from mirrors and sound reflects from hard surfaces
What are some real-world examples of refraction?
Light bends when it passes from air into glass or water
What is a reason you can hear sound around corners?
Due to diffraction, sound bends around obstacles like walls and buildings
What suggests light waves have very short wavelengths?
Light spreads when it passes through tiny holes and slits. Due to diffraction, this suggests light waves have very short wavelengths
What suggests radio waves have long wavelengths?
Some radio signals can bend around large obstacles like hills. Due to diffraction, this suggests radio waves have very long wavelengths
How do you hear sound (simple)?
Sound waves reach your ear and make your ear-drums vibrate, making you hear a sound
What causes sound waves?
Vibrations
What are some objects which produce sound waves through vibrations?
Guitars (vibrating strings), trumpets (vibrating air inside) and tuning forks (vibrating prongs)
How does air pressure vary in compressions and rarefactions?
Air pressure is higher than average in compressions and lower than average in rarefactions
