Flashcards in Topic 2- Waves And Electromagnetic Spectrum Deck (84):
Transverse wave have vibrations which...
Are perpendicular to the direction the wave travels
Examples of transverse waves are...
All electromagnetic waves
Ripples and waves in water
Longitudinal waves have.... vibrations
Parallel vibrations to the direction the wave travels
What do longitudinal waves do to the particles
Squash up and stretch out the arrangement of particles in the medium they pass through
Therefore making compressions (high concentrations of particles- high pressure) and rarefactions (low concentrations of particles- low pressure)
Examples of longitudinal waves are...
Energy and information in the direction they are travelling
When a wave travels through a medium...
The particles vibrate and transfer energy and information between each other up but overall the particles stay in the same place
The displacement from the rest position to a crest or trough
The wavelength is...
The length of a full cycle of the wave
The number of complete cycles of the wave passing a certain point per second
Measured in hertz
eg. 1Hz is one wave per second
The period of a wave is...
The number of seconds it takes it takes for one full cycle
Period = 1 / frequency
Tells you how quickly a wave moves through space
Two calculations for wave speed
Wave speed = distance / time
Wave speed = frequency X wavelength (called wave equation)
When a wave meets a boundary between two materials three things can happen...
Absorbed ... by the second material, the wave transfers energy to the materials energy store (often transferred to a thermal energy store, leading to heating eg. microwaves)
Transmitted ... through the second material, the wave carries on travelling through the new material (can be used in communications and lenses for glasses and cameras)
Reflected ... sent back away from the material (how echos are created)
Refraction occurs when...
A wave hits a boundary at an angle, this change of speed (because of change of density) causes a change in direction
Wave travelling along a normal...
But change in speed
Greater the change in speed...
The more a wave bends (changes direction)
If the wave speeds up...
Speeds up... bends away from the normal
Slows down... bends towards the normal
How much EM waves refract is affected by...
Wavelength, shorter wavelengths bend more
Can lead to dispersion
eg.white light becoming a spectrum
Frequency... when crossing a boundary
Stays the same
Change of speed is caused by...
A change in wavelength
Wavelength decreases if the wave slows down and increases if the wave speeds up
Sound waves are...
When sound waves travel through a solid...
It causes particles in the solid to vibrate, but not all frequencies can be transferred through an object
What determines which frequencies can be transmitted
Size, shape and structure
Sound travels ... in liquids than they do in gases and ...in solids than they do liquids
Faster in liquids than gas
Faster in solids than liquids
Sound waves wavelengths...
When slowed down they get shorter
When speeded up they get longer
Reflected sound waves
Sound waves will reflect at hard, flat surfaces
Sound waves in a vacuum
Sound waves can’t travel in a vacuum
Because there are no particles to move or vibrate
Causes the sound waves to vibrate
Tiny bones which pass the vibrations through the semicircular canals and to the cochlea
Turns the vibrations into electrical signals which gets sent to the brain
Sends signals to the brain
The brain interprets the sound depending on the intensity and frequency
Eg. high frequency waves as high pitch sounds
Human hearing is limited...
By shale and size of eardrum
And structure of the parts that vibrate to transmit the sound wave
A frequency of higher than 20,000 Hz
Ultrasound waves get...
Partially reflected and partially refracted
Uses for ultrasound
Medical imaging... scanning for a baby
Reach the womb, some waves get reflected others refracted and the exact distribution and timing of the echos produces an image of the foetus- completely safe
Industrial imaging... finding flaw in materials
Waves reflected by far side of material, if there is a flaw in the material the waves will be reflected sooner
Underwater to find the distance to the seabed or locate objects in deep water
Frequencies lower than 20 Hz
Uses for infrasound
Some animals communicate using infrasound like elephants and whales
Erupting volcanos, avalanches and earthquakes produce infrasound, so scientists can study and monitor levels of infrasound to predict events
Earthquakes produce waves which travel through the different layers i of earth, some are infrasound, we can use these waves to explore the structure of the earth
Seismic waves are produced by...
Explosions and earthquakes at a range of frequencies which are spent through the earth
Seismic waves can be detected using a ...
Seismologists work out how long it take for the waves to reach the seismometer and what parts of earth don’t receive the waves
When seismic waves reach a boundary at the different layers in Earth...
The change of density and properties causes some of the waves to be absorbed and refracted
Mostly when the waves are refracted they change speed...
Gradually resulting in a curve path
When the properties change suddenly, the wave speed changes abruptly and the path has a kink
P-waves inside the earth are...
Travel through solid and liquids
They travel faster than S-waves
S-waves inside the earth are...
Only travel through solids
Slower than P-waves
Reflection angles rule...
Angle of incidence = Angle of reflection
Angle of incidence is...
The angle between the incoming wave and the normal
Angle of reflection is...
The angle between the reflected wave and the normal
The normal is...
The imaginary line that’s perpendicular to the surface at the point of incidence (the point the wave hits the boundary)
Shown as a dotted line
Total internal reflection is less than the critical angle...
Most of the last that is refracted into the outer layer, but some of it is internally reflected
Total internal angle is equal to the critical angle...
The ray would go along the surface
With quite a bit of internal reflection
Total internal reflection is larger than the critical angle...
No light comes out
It’s all internally reflected
i.e. total internal reflection
Total internal reflection is...
When a wave is reflected back into a material
Can only happen if the wave travels through a dense material like glass or water towards a less dense substance like air
Every material has its own, different critical angle
Speculator reflection is...
When waves are reflected in a single direction by a smooth surface
Means you get clear reflection
Eg. When light is reflected by a mirror
Diffuse reflection is...
When a wave is reflected by a rough surface (eg.paper) and the wave is reflected in all directions
This is because the normal is different for each incident ray, so each day has a different angle of incidence
Surface looks matt and you don’t get a clear reflection
White light is...
A mixture of all the different colours of light which all have different wavelengths
Opaque objects are objects that...
Do not transmit light
They absorb some wavelengths of light and reflect others
The colour of an opaque object depends on...
What wavelengths of light are reflected
White objects reflect...
All the wavelengths of visible light equally
Black objects absorb...
All wavelengths of visible light
Objects transmit light, not all the light is absorbed or reflected some...
Light can pass through
Partially see through
Objects transmit light, not all the light is absorbed or reflected some...
Light can pass through
Colour filters are used to filter out...
Different wavelengths so only certain wavelengths (colours) are transmitted and the rest are absorbed
Bulges outwards in the middle
Causes parallel rays of light to be brought together t the principal focus
Caves inwards in the middle
Causes parallel rays of light to spread out
Principal focus for converging and diverging lens
Principal focus of a converging lens is where the rays hitting the lens parallel to the axis all meet
Principal focus of a diverging lens is the point where rays hitting the lens parallel to the axis appear to all come from
A real image is...
Formed when the light rays actually come together to form an image
Can be captured on a screen
Eg. The image is formed on the eyes retina
A virtual image...
Is when the light rays from the object appear to be coming from a completely different place to where they’re actually coming from
Cannot be captured on a screen
Eg. Magnifying glasses create virtual images
Focal length is...
Related to the power of the lens
Eg. The more powerful the lens, the more strongly it converges rays of light, so the shorter the focal length
Power for converging and diverging lens
Converging lens - positive power
Diverging lens - negative power
Order of frequency and wavelength of the electromagnetic spectrum
Microwaves- Longest wavelength and lowest frequency
Gamma rays- Shortest wavelength and highest frequency
Electromagnetic waves all travel through a vacuum at .......... but Tavel through different materials at ............
Different speeds (leading to refraction and dispersion)
Colours of visible light in order of wavelength
Orange - longest wavelength
Violet - shortest wavelength
All electromagnetic waves transfer ..... from a ..... to an .......
The higher the frequency of an EM wave the ............ it transfers (making it ........... for humans)
Radio waves and the human body
Are transmitted through the body without being absorbed
Microwaves and the human body
Some wavelengths can be absorbed causing a heating of cells which can be dangerous
Infrared and visible light and the human body
Are mostly reflected or absorbed by the skin causing some heating.
IR can cause burns if the skin gets too hot
Ultraviolet and the human body
Absorbed by the skin
More dangerous because of the higher frequency
Type of ionising radiation which means when it is absorbed it can cause damage to cells on the surface of you skin, can lead to skin cancer
Can damage eyes
X rays and gamma rays and the human body
Ionising, so can cause mutation and damage to cells
Higher frequencies cause even more damage
Deeper tissue can absorb the energy
The distribution and intensity of the wavelengths (of EM emitted and absorbed) ONLY depends on the objects...
The power per unit area
As the temperature of an object increase the intensity of every emitted wavelength ...