Flashcards in P4: Waves Deck (29):
1
Transverse waves
The oscillations are perpendicular to the direction of energy travel. Examples are:
All EM waves
Seismic waves
Ripples
2
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:
Sound
P waves
3
V = x/t
Wave speed = distance/time
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V = f x λ
Wave speed = frequency x wavelength
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Oscilloscope
You can use two microphones and an oscilloscope to find the wavelength of a sound
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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
7
Refraction
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
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Sound
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
9
Ear
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
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Ultrasound
Ultrasound is sound with frequencies higher than 20000Hz. This is outside human hearing range
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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
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Infrasound
Infrasound is sound with frequency’s lower than 20Hz
Under our hearing
Uses
Some animals use this to communicate
Detecting seismic activity as they release these
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Reflection
The law of reflection - angle of incidence = angle of reflection
14
what do waves transfer and not transfer
- energy and information
- not matter
15
what is the frequency of a wave
number of waves passing a point each second
16
what is the equation for the velocity of a wave using frequency
v = f * wavelength (lambda)
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example of a transverse wave
light
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example of a longitudinal wave
sound
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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
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what is the period of a wave
- the number of seconds it takes for one full cycle
- period = 1 / frequency
21
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
22
what is ultrasound
sound with a frequency greater than 20,000 hz
23
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
24
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
25
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
26
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)
27
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
28
how can you measure how fat away a boundary is when using ultrasound
the time it takes for the reflections to reach a detector
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