5.1 - Wave behaviour Flashcards
How do waves transfer energy?
o When waves travel through a medium, the particles of the medium vibrate and transfer energy between each other
o But overall, the particles stay in the same place – only energy is transferred
Amplitude
The amplitude of the wave is the displacement from the rest position to a crest or a trough
Wavelength
The wavelength is the length of a full cycle of the wave
e.g. from crest to crest
Frequency
The number of complete waves or cycles passing a certain point per second
Measured in hertz (Hz)
1 Hz is 1 wave per second
Period of wave
A period of a wave is the number if seconds it takes for one full cycle
Period = 1 ÷ frequency
Transverse waves
In transverse waves the vibrations are perpendicular ( at 90°) to the direction the wave travels
Examples of transverse waves
All electromagnetic waves – lights
S waves
Ripples and waves in water
Longitudinal waves
In longitudinal waves the vibration are parallel to the direction the wave travels
Examples of longitudinal waves
Sound waves
P waves
Wave speed equation
Wave speed (m/s) = frequency (Hz) x wavelength (m)
1 kHz = 1000 Hz
1 MHz = 1 000 000 Hz
When a wave meets a boundary between two materials what three things can happen?
The wave may be absorbed by the second material, transferring energy to the materials energy stores
The wave may be transmitted – it carries on travelling through the new material, often at a different speed (velocity) which can lead to refraction
The wave may reflect off a boundary – this is where the incoming ray is neither absorbed nor transmitted but ‘sent back’ away from the second material
Angle of incidence = Angle of Reflection
Each angle is measured from the normal – line that’s at the right angles to the surface at the point the light hits it (drawn with dotty line)
What lets you see things?
The reflection of visible light – light bounces off objects and into our eyes
Light rays reflecting of smooth and rough surfaces
Light rays reflect of smooth surfaces (e.g mirror) all in the same direction, giving a clear reflection
Light rays reflect off rough surfaces (e.g paper) in all different directions.
The angle of incidence still equals the angle of reflection for each ray but the rough surface means each ray hits the surface at a different angle and so is reflected at a different angle, scattering the light
White light
White light is a mixture of all the different colours of light which all have different a wavelength
All the colours of light in white light are reflected at the same angle – white light doesn’t split into different colours when it reflects as all the wave lengths follow the rule above
Refraction
The change in direction of a wave when its speed changes as a result of going from one medium to another
Explain how a wave changes speed?
a wave crosses a boundary between materials e.g from glass to air, the densities of the materials are different, so it changes speed
What happens to the frequency of a wave when it crosses a boundary?
Stays the same
What happens to wavelength if the wave slows down?
It decreases
What happens to wave length if wave speeds up?
It increases
If wave slows down
it will bend towards normal
If the wave speeds up
it bends away from the normal
How does sound travel in denser material?
faster
How do Electromagnetic (EM) waves travel in denser materials?
EM waves like light usually travel slower in denser materials
Specular reflection
When waves are reflected in a single direction by a smooth surface
How does scattering occur?
When waves are reflected by a rough surface and the waves are reflected in all directions
this happens because the normal is different for each incident ray so each ray has a different angle of incidence
