Waves
Wave Basics
Waves can be described by...
Frequency - the number of waves passing a point each second. Measured in hertz (Hz).
Speed - measured in meters per second (m/s)
Wavelength - the distance between two equivalent adjacent points on a wave, peak-peak or trough-trough
Amplitude - the maximum displacement of a point on a wave from its undisturbed position
Period - the time taken for one wavelength to pass a point
Longitudinal waves
Direction of wave travel is parallel to direction of energy transfer
Sound waves and seismic P waves
contain compressions and rarefractions, when the wave spreads out and gets closer
Transverse waves
Direction of wave travel is perpendicular to the direction of energy transfer
Electromagnetic waves and seismic S waves
Wave equation
Velocity = frequency X wavelength
Waves at boundaries
Whenever a wave reaches the boundary between two materials, the wave can be: reflected, refracted, transmitted or absorbed
Reflection
Angle of incidence = Angle of reflection
Waves are transmitted when they pass through a body, radio waves passing through walls.
Waves are absorbed when they are taken in by a body and don't pass through it, like microwaves absorbed by food
Refraction
The change in direction of a light ray when it travels from one medium density to another
Less dense to more dense = bends towards the normal
More dense to less dense = bends away from the normal
Rays of light that meet at 90 degrees dont bend
Hearing
Sound waves cause your ear drum to vibrate
The vibrations are passed on to tiny bones in the ear called ossicles, throught the simicircular canals and to the cochlea
The cochlea turns the vibrations into electrical signals
The signals get sent to the brain and allow you to hear
Humans can only hear sounds between 20Hz and 20,000 Hz
The limits are caused by the size and shape of our ear drum
Ultrasound
Sound waves with a frequency greater than 20,000 Hz
Properties
When waves pass from one medium to another, some are reflected and some are transmitted. This is called partial reflection
If you point a pulse of ultrasound at an object, some of it will be reflectd back
When sound waves are reflected by surfaces, there is a delay between you hearing the original sound and the reflected sound
Reflected waves have to travel further, taking longer to reach our ears. This is known as an echo
The time it takes for the relfections to reach a detector can be used to measure how far away a boundary is
Uses
Medical imaging
Used in pregnancy scans
Some of the waves are refelcted back and detected
The exact timing and distribution of the echoes can produce a video image of the foetus
Industrial imaging
Can find flaws in pipes
Ultrasound waves will usually be reflected by the far side of the material
Echo sounding
Used by boats and submarines
Used to find the depth of the water or locate objects
When calculating the distance, divide by 2 because the wave has travelled to the sea bed and back
Seismic waves
Earthquakes produce seismic waves which travel through the earth
P - waves, longitudinal and can travel through solids and liquids
S - waves, transerse and can only travel through solids, can't pass through liquids
P waves travel faster than S - Waves
Exploring the earth
Seismic waves can be detected at different points on the surface, using detectors called seismometers
Seismologists work out the time it takes for the shock waves to reach the seismometer
Data can be used to uderstand the structure of the earth since we know that P waves can travel through liquid and solids while s waves can't travel through liquids
When the medium the waves are travelling through suddenly changes, the direction changes, and the path has a kink
By measuring the seismic waves detected at various points, the paths the waves have travelled along can be created, and the different boundaries between materials can be figured out
If there is a crack, the waves will be reflected from it, and be detected sooner
Measuring the speed of sound
Measure the distance from the sourc eof the sound to the reflecting surface (wall)
2) Using a stopwatch measure the time interval between the original sound being produced and the echo being heard
3) Use the equation speed = distance / time
Repeat the experiment at a range of distances to obtain accurate and precise results
Specular reflection - Waves reflecting off smooth surface
Diffuse reflection - Waves reflecting off rough surface
Transmission
Waves passing through transparent material
More transparent the material is the more light that passes through
Waves refraction is still transmisison
Can be damaged by repeated loud noises