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Wave definition
an oscillation (vibration) that transfers energy and information (not matter) from one place to another
Wavelength definition
length of a full cycle e.g. crest to crest
Amplitude
size of wave (1/2 crest to trough)
Frequency definition
number of complete waves to pass a point per sec
Period definition
time taken to move through one complete cycle
Velocity definition
speed in a stated direction
wave speed (with frequency and wavelength)
speed = frequency x wavelength
Transverse wave
Vibrations are perpendicular to direction of transfer
Longitudinal wave
Vibrations are parallel to direction of transfer
Crest
highest point of wave
Trough
lowest point of wave
Equilibrium
middle point of wave
Wavefront
all locations where wave is in the same phase e.g. all troughs
Period equation
1 / frequency
Frequency equation
1 / period
Reflection
when a wave bounces off a surface at an angle and changes direction
Refraction
when light changes speed between different media
Transmission
when a wave passes through a material
Absorption
when a wave is taken in and the energy is transferred to the material
Refraction: when the wave gets faster…
it bends away from the normal
Refraction: when the wave gets slower…
it bends towards the normal
Range that humans can hear
20Hz - 20,000Hz
Ultrasound definition
very high sounds humans can’t hear above 20,000Hz
Infrasound
very low sounds humans can’t hear below 20Hz
Auditory nerve
electrical signals carry messages along this to the brain
Eustachian tube
tube that connects ear and nose
Ear canal
tube that carries sound to the inner ear
Pinna
visible part of the ear, collects sound waves and funnels them into the ear
Eardrum
thin membrane that vibrates when sound waves hit it
Ossicles
made up of the stirrup, anvil and hammer
they help transmit vibrations to the inner ear
Semi-circular canals
help you balance
Cochlea
snail shaped and full of cilia (tiny hairs) that convert vibrations into electric signals (aka nerve impulses)
The base is thicker and stiffer than the apex, and vibrates at higher frequencies.
Measuring waves in a ripple tank practical
Count how many waves are formed in 10secs
Put a ruler against the tank and use it to measure the length of the waves (easier to take a photo and measure off that)
Measure the distance between two points and see how long it takes waves to go from one part to another
To get frequency divide the number of waves in 10s by 10 (step 1)
To get speed divide the distance by the time (both from step 3) OR Multiply the wavelength (step 2) by frequency (above)
Ultrasound sonar
Ship emits ultrasound wave downwards
Wave reflects off seabed and returns to the ship
Speed = distance/time is used to calculate depth of seabed (distance) as instruments on the ship measure the speed & time of the wave
Ultrasound scanning
Transducer (or probe) is placed against skin
Gel is used to stop waves reflecting off skin
Transducer emits ultrasound waves and measures how long it takes for them to bounce off something and come back
Shorter time = closer object
Speed = distance/time used for exact distance calculations
An image can also be made if you know how far away lots of things are
P waves
longitudinal waves, travel through both solids and liquids
S waves
transverse waves, only travel through solid
Infrasound and the earth’s core
The properties of the earth change as you go deeper
The S wave shadow zone means that there is something liquid in the centre of the earth stopping the S waves going through, as they can’t travel through liquids (the mantle)
When P waves pass in and out of the liquid mantle, the refract and change direction
The few weak waves received in the P wave shadow zone are because of the solid inner core
This happens no matter where the earthquake is
Seismic waves
waves produced by earthquakes
Seismometers
instruments that detect/measure seismic waves
Example of a transverse wave
visible light wave
Example of a longitudinal wave
sound wave
Note
Flashcard