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Flashcards in P4: Waves Deck (29):

Transverse waves

The oscillations are perpendicular to the direction of energy travel. Examples are:
All EM waves
Seismic waves


Longitudinal waves

The oscillations are parallel to the direction of energy travel
The waves squash up and spread out making compressions and rarefactions
Examples are:
P waves


V = x/t

Wave speed = distance/time


V = f x λ

Wave speed = frequency x wavelength



You can use two microphones and an oscilloscope to find the wavelength of a sound


Wave behaviour at boundaries

When a wave meets a boundary three things can happen
1. Absorption by the second material - usually turned into thermal energy
2. Transmission through the second material (refraction)
3. The wave is reflected



Waves at different speeds in materials with different densities so when a wave hits a boundary it changes speed
If this happens at an angle the wave will change direction (refraction) this will always bend towards the normal
Because different colours of light have different wavelengths this can lead to the wavelengths splitting up if the 2 ended of a block of glass are not parallel the spectrum will not turn back into white light



These are caused by vibrating objects these vibrations cause compressions and rarefactions in the air
Sound waves can refract as they enter materials
Sound waves can be reflected by hard surfaces as it is harder for them to travel through these (echos)
No sound in space because it is a vacuum



When a sound wave meant your ear drum it causes it to vibrate
These vibrations are passed on to tiny bones called ossicles through the semicircular canals and into the cochlea
These get turned into electrical signals that go to your brain



Ultrasound is sound with frequencies higher than 20000Hz. This is outside human hearing range


Ultrasound uses

Medical imaging - ultrasound imaging is used as the waves can pass through the body but When they meet a boundary they reflect so you see the reflections of the foetus
Industry- find a flaw in a material

Echo sounding



Infrasound is sound with frequency’s lower than 20Hz

Under our hearing

Some animals use this to communicate
Detecting seismic activity as they release these



The law of reflection - angle of incidence = angle of reflection


what do waves transfer and not transfer

- energy and information
- not matter


what is the frequency of a wave

number of waves passing a point each second


what is the equation for the velocity of a wave using frequency

v = f * wavelength (lambda)


example of a transverse wave



example of a longitudinal wave



what is amplitude and what is it responsible for

amplitude is the vertical length of a wave from the rest position (line drawn through the middle)
- `and is responsible for the distance an object travels to make noise


what is the period of a wave

- the number of seconds it takes for one full cycle
- period = 1 / frequency


how do longitudinal waves travel

- longitudinal waves squash up and stretch out the arrangement of particles in the medium they pass through
- making compressions and rarefactions


what is ultrasound

sound with a frequency greater than 20,000 hz


how is the distance between a ship and the seabed figured out with ultrasound

- pulse of sonar is shot from the ship to the seabed
- the echo of it is detected
- time taken for the echo to travel back to the ship / 2 (with the speed of ultrasound in water known) allows them to calculate the depth of seabed


explain how ultrasound is used in foetal scanning

- ultrasound is shot at the foetus with an ultrasound transmitter
- when it reaches a boundary between 2 different media
- like the fluid in womb and skin of foetus
- some of the wave is reflected back
- exact timing and distribution of echoes are processed by a computer to produce a video image


how is ultrasound used in the body for scanning

- ultrasound shot at person
- between 2 different media some of it is reflected back and processed by a computer (echoes)
- a video image is shown


what happens to a wave when it passes from one medium into another

- some of the wave is reflected off the boundary between the two media
- some is transmitted and refracted (partial reflection)


how is the way a wave reacts when passing through two media used with pulses

- you can point a short burst of ultrasound at an object
- wherever there are boundaries between one substance and another, some ultrasound gets reflected back


how can you measure how fat away a boundary is when using ultrasound

the time it takes for the reflections to reach a detector


what is ultrasound used in

- medical imaging like pre-natal scanning of foetus
- industrial imaging like finding flaws in amterials
- echo sounding