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