Section 3 - Waves And The Electromagnetic Spectrum Flashcards
What do waves transfer?
Energy
Information
What do particles in a wave do?
Vibrate
What is the amplitude of a wave?
The displacement from the rest position to the trough or the crest
What’s the wavelength of a wave ?
The wavelength of a wave is length of a full cycle of the wave
Distance between 2 identical points
What’s the frequency of a wave ?
What’s frequency measured in?
The frequency of a wave is Number of complete cycles of the wave passing a certain point per second.
Frequency is measured in hertz(hz)
1hz is one wave per second
What’s the period of a wave?
How do we calculate the period of a wave?
The period of a wave is the number of seconds it takes for a full cycle of a wave to pass a certain point
Period= 1/frequency
What type of vibrations do transverse waves have?
Real life example of one
The vibrations are perpendicular to the direction a wave travels
A spring wiggled up and down gives a transverse wave.
Examples of transverse waves …
- all electromagnetic waves
- S-waves ( a type of seismic wave)
-ripples and waves in Water
The vibrations in a longitude wave …
What do they do as they travel through a medium?
What does this cause?
In longitudal waves, the vibrations are parallel to the direction of travel of the wave
They squash up and stretch out the arrangement of particles in the medium as they pass through.
This makes compressions (high pressure) and rarefractions ( low pressure)
Examples of longitudal waves…
Sound waves
P-waves
What is wave speed?
Wave speed is how quickly a wave moves through a place
2 ways to calculate wave speed?
Wave speed = distance/time
Wave speed=frequency(Hz) X wavelength (m)
Equipment to measure the speed of sound?
oscilloscope
Signal generator
Two microphones
Speaker
How do we measure the speed of sound?
-Set up the oscilloscope so the detected waves at each microphone are shown as separate waves
-start with both microphones next to speaker then move one away until two waves are aligned on the display but have moved one wavelength apart
-measure distance between the microphones to find one wavelength
-use the formula v= frequency X wavelength to find the speed of sound waves passing through the air
How to measure the speed of water ripples using a strobe light ?
1)Using a signal generator attached to the dipper of a ripple tank create water waves at a set frequency.
2)dim lights and turn on a strobe light. You’ll see a pattern of waves below
3) alter the frequency of the strobe light until the wave pattern on the screen appears to freeze and stop moving. This happens when the frequency of the waves and the strobe light are equal
4) the distance between each shadow line is equal to one wavelength. Measure distance between lines that are 10 wavelength apparent then find avaradhe wavelength
5) use v=frequency X wavelength to find the speed of the waves.
How do we find speed of waves in a solid ?
Measuring the frequency of sound waves produced when you hit the object
Hitting the rod causes waves to be produced along the rod
These make the rod vibrate and produce sound waves in the air around the rod
These sound waves have the same frequencies as the waves on the rod
Method of finding wave speed in a solid…
1) measure and record the length of a metal rod
2) set up apparatus. Rod attached to clamps by elastic bands, microphone attached to computer on the left of the rod. Hammer on the right of the rod
3) tap the rod with the hammer. Write down the peak frequency displayed by the computer
4) repeat this three times to get an avaradhe peak frequency
5)calculate speed of the wave by using v=frequency X wavelength. The frequency is represented as the rod length X 2
What can waves do at boundaries ?
Be absorbed
Reflected
Transmitted
Refracted
What happens when a wave is absorbed at a boundary?
The wave transfers energy to the materials energy stores
What happens when a wave is transmitted at a boundary ?
The wave carries on travelling through the new material. This often leads to refraction. Refraction can be used in communications
What does what happens to a wave as it reaches an interface depend on?
Wavelength
Properties of the material involved
What can happen at a boundary causing a wave to refract?
The wave changes speed
What happens if the wave hits the boundary at an angle?
The change in speed will cause a change in direction- refraction
What happens in the wave is travelling along the normal ?
The wave will change in speed but not be refracyed
The greater the change in speed …
The more a wave bends
What happens if a wave bends towards the normal?
Away from the normal?
It slows down if it’s travelling towards the normal
It speeds up if it’s travelling away from the normal
How do em waves normally travel in denser materials
Slowly
What effects how much an em wave refracts?
It’s wavelength. Shorter wavelengths bend more
What happens if the wavelength decreases when light travels through a boundary ?
The wave slows down
If it increases, it speeds up
What’s the angle of incidence?
The angle of incidence Is the angle between the ray and the normal
What happens if the second material is denser than the first?
What happens if it’s less dense than the first?
The refracted ray bends towards the normal
The refracted ray will bend away from the normal(angle or refraction is larger than the angle of incidence)
Environment needed for the refraction practical?
Dim room so you can clearly see the ray
Ray of light must be thin
Use a ray box that has a lightbulb in it
How to carry out the core practical that investigates light refracting at the boundary between air and glass ?
1) place a rectangular block on a piece of paper and trace around it. Use a ray box to shine light at one side of the block
2) trace the incident ray and emergent ray on the other side of the block. Remove the block and with a straight line join up the incident ray and emergent ray to show the path of the refracted ray
3) draw the normal at the point where the light ray entered block. Use a protractor to measure the angle of incidence and the angle of refraction. do the same for the point where the ray emerges from the block
4)repeat three times keeping the angle of incidence where the ray enters the block the same. Calculate the averages for each of the angles
What you should find from the refraction practical
-Light bends towards the normal as it enters the block. This is because the air has a lower density than glass, so the light ray will always slow down when it enters the block.
- you should then see the light ray bends away from the normal as it leaves the block, this is because light rays speed up as it leaves the block and travels through air
What’s the law of reflection?
angle of incidence = angle of reflection
What does total internal reflection depend on?
The critical angle
What does total internal reflection mean?
reflected back into the material
Where can total internal reflection occur?
When a wave travels through a dense material into a less dense substance
Angle of incidence larger than the critical angle
What’s needed for total internal reflection to occur?
The angle of incidence must be larger than the critical angle . Every boundary has its own different critical angle
What’s specular reflection ?
When waves are reflected in a single direction by a smooth surface
What’s the result of specular reflection?
Example.
You get a clear reflection.
Eg: light reflected by a mirror
What is diffuse reflection?
Diffuse reflection occurs when waves are reflected by a rough surface And waves are reflected in all directions
Why does diffuse reflection occur?
Diffuse reflection occurs because the normal is different for each incident ray
What does the surface of diffuse reflection look like?
The surface looks matte, you don’t get a clear reflection
What are sound waves caused by?
Vibrating objects
What type of wave are sound waves ?
What happens when they travel through a medium?
What happens when they travel through a solid?
Sound waves are Longitudal waves
The vibrations are passed through a medium as a series of compressions and rarefractions
When sound waves travel through a solid they do so by causing particles to vibrate
What determines the frequencies of sound an object can transmit?
Size
Shape
Structure
Of the object
What do sound waves travel the fastest - slowest in
Fastest = solids
Liquids
Slowest = Gasses
How does the Wavelength change as the wave speed does?
It gets longer when the wave speeds up. Shorter when it slows down
What causes echoes/sound waves being reflected
Hard/flat surfaces
Why can’t sound waves travel in space?
Because it’s mostly a vacuum.
There are no particles to move or vibrate
How do we hear sound ?
1)Sound waves reach the ear drum and vibrate
2)these vibrations are passed on to tiny bones called ossicles, through semicircular canals to the cochlea.
3) the cochlea turns these vibrations into electrical signals which get sent to the brain.
4) the brain interprets these signals as sound of different volumes, depending on their frequency and intensity. A higher frequency sound wave has a higher pitch.
What’s human hearing limited by ?
Size and shape of our eardrum. The structure of all the parts within the ear that vibrate to transmit the sound wave
What is infrasound?
Frequencies with lower than 20hz
Animals that communicate using infrasound..
Elephants and wales. Scientists are able to track these animals for conservation purposes
How can scientists predict that a volcano is about to erupt?
By using infrasound. Volcanoes avalanches and earthquakes produce infrasound
What is ultrasound?
Frequencies with higher than 20000 hz
What happens to ultrasound waves when they reach a boundary?
Somme are reflected, some refracted
How it useful ultrasound is partially reflected at a boundary between mediums ?
You can point a pulse of ultrasound at an object, wherever there are boundaries between substances some of the ultrasound is reflected back.
The time it takes for reflections to reach a detector. Can. Be used to measure how far away a boundary is
What can ultrasound be used in?
Medical imaging
Eg: scanning a foetus
Industrial imaging.
Eg: finding flaws in objects such as pipes of materials such as wood or metal
How do ultrasound waves work?
Pass through the body but when they reach a boundary between two different media they are partially reflected and detected.
The timing and distribution of these echoes is processed by a computer to produce a video image of the foetus. Completely safe
Used in sonars by boats to find the distance to the sea bed or locate objects in deep water
What waves does an earthquake produce?
How do we detect them?
Seismic waves at a range of frequencies.
We detect them using seismometers.
What have scientists been able to work out from observing how seismic waves are absorbed and refracted ?
Where the properties of the earth change dramatically.
What are the two different types of seismic waves ?
P waves
S waves
What are P-waves?
What can they travel through?
Are they taste or slower than S-waves?
What material are they the fastest in ?
P-waves are Longitudal
P-waves can travel through solids and liquids and gases
They travel faster than S-waves
They’re the fastest in solid
What are S-waves ?
What can S-waves travek through?
Are S-waves faster or slower than P-waves?
S-waves are transverse
S-waves can travel through solids NOT liquids
S-waves are slower than P-waves
What waves can travel through the earths core (S-waves or P-waves)
Why?
P-waves can travel through the earths core.
S-waves can’t because the earth has a liquid outer core and S-waves can’t travel through liquids
How do we perceive different colours differently ?
Based on their wavelength
What part of the electromagnetic spectrum can our eyes detect?
Visible light
What is white light ?
White light is a mixture of all the different colours of light
Why do opaque objects not transmit light ?
What does the colour of an opaque object depend on?
They absorb some wavelengths and reflect overs.
Which wavelengths of light are reflected , they absorb some wavelengths and reflect others
Why might a banana appear yellow… 2 two reasons
It’s reflecting the yellow light or it’s reflecting both red and green
What do white objects reflect ?
All the wavelengths of visible light equally
Black objects also absorb all the wavelengths of visible light
What do transparent and translucent objects appear see through ?
Because they can transmit some of the light
What do colour filters only let through ?
Particular wavelengths
How do colour filters work to show a colour?
Colour filters are used to filter out different wavelengths of light so that only certain wavelengths are transmitted, the rest are absorbed
How do filters that aren’t made for primary colours work?
They let through both wavelengths corresponding to that colour.
What do lenses do ?
Refract onto form light from an image
What does a converging lens do ?
What does it look like ?
Where does it cause light to end up
It causes parallel rays of light to be bought together at the principal focus
A converging lens bulges outwards towards the middle
There sometimes called convex lenses
What does a diverging (concave) lens do? And what does it do to light
A diverging lens caves inwards . It causes parallel rays of light to spread out
What’s the distance from the centre of the lens to the principal focus called ?
Focal length
Diagram of converging lens ?
Diagram of diverging lens
Two types of images lenses can refract light to form?
A real image
Virtual image
What does how much lenses refract light depend on?
Power of the lens
How is a real image formed with a lens ?
When light rays actually come together to form the image. It’s captured on a screen, the light rays actually meet at a place where the image seems to be.
How is a virtual image formed by a lens ?
Example
A virtual image is when light rays from the object appear to be coming from a completely different place to where they’re actually coming from. Light rays don’t come together where the image seems to be coming from
Example - magnifying glass creates virtual images
What increases the power of the lens ?
The curvature
What does it mean if a lens is powerful and converges light very strongly?
It has a short focal length
For a converging lens, the power of a lens is ….
Positive
For a diverging lens the power of the lens is …
Negative
How do you make a more powerful lens?
Add strongly curved surfaces
Diagram of a ray diagram for a diverging lens.
Diagram of a ray diagram through a converging lens …
What will the image be if the object is placed at 2F from the lens ?
A real, inverted image the same size as the object will be produced. 2 F on the other side of the lens
What image will be produced if the object is placed between F and 2F ?
Between F and 2F a real, inverted image bigger than the object will be produced. Shown at more than 2 f on the other side of the lens
What image will be produced from an object that’s placed nearer than F from a lens ?
A virtual upright image bigger than the object and on the same side of the lens
What are electromagnetic waves. Longitudal or transverse?
Electromagnetic waves are Transverse waves
What do all EM waves travel the same speed in.
What do they travel different speeds in.
All EM waves travel at the same speed through a vacuum
They travel at different speeds through different materials
Order of the EM waves
Rabbits - radio (Longest wavelength)
Mate - Microwaves
In- Infared
Very- Visible light
Unusual-ultraviolet
Expensive- X-rays
Gardens - gamma rays (highest frequency )
What do em waves transfer ?
All EM waves transfer energy from one source to another absorber.
What does a higher frequency EM wave mean ?
The higher the frequency of the EM wave , the more energy it transfers and so is more dangerous to humans
What are radio waves made by?
Oscillating chargers
What are EM waves made up of
Oscillating electric and magnetic fields
What will the frequency of the waves produced be equal to?
The frequency of the alternating current
How can you produce radio waves ?
Using an alternating current in an electrical circuit.
What are radio waves used for ?
Communication and broadcasting
How are short-wavelength radio signals possible
They are reflected by the atmosphere
How are long-wavelength radio signals possible?
They bend around the surface of the earth
What waves do satellites use ? 2 of them
Microwaves
Radio waves
How does satellite tv work in space ?
The signal from a transmitter is transmitted into space and picked up by the satellite receiver dish orbiting thousands of km above the earth.
The satellite transmits the signal back to the earth in a different correction where it’s received by a relate dish on the ground
What types of waves do microwaves use?
How does a microwave work?
-Microwaves
-1)the microwaves are absorbed into the food.
2)the microwaves penetrate up to a few centimetres into the food before being absorbed and transferring the energy they are carrying the water molecules in the food, causing the water to heat up.
3) these water molecules then transfer this energy to the rest of the molecules in the food by heating , which cooks the food
Uses of infrared ?
Monitoring temp.
Cooking food.
Changing the tv channel
Short communication
What do all objects give out ?
What happens to the level of it there is the hotter the object gets ?
What happens when a camera detects it?
Infrared radiation. The hotter the object the more it gives out.
Infared cameras can be used to detect and infared radiation and monitor temp.
When a camera detects IR radiation it turns it into electrical signal which is then displayed on as screen as a picture
How does infared radiation heat things up ?
Long pieces of write that heat up when a current flows through them. The wire then emits a lot of infared radiation. The emitted Ir radiation is absorbed by all the objects in the room.
How does infared transfer information?
Send files between mobile phones or laptops. Small distances.
What are optic fibres ?
How do they prevent dispersion?
What do they use to send data over long distance
Thin glass or plastic fibres that carry data over long distances as pulses of infared radiation .
They are a single wavelength to prevent dispersion.
They use total internal reflection to send data over long distances
What is visible light used for ?
Photography
How do digital cameras use visible light to create an image ?
Digital cameras contain image sensors which detect visible light and generate an electrical signal
What ultraviolet used for ?
-Fluorescent lamps
-Bank notes and passports to detect forgeries
-Sterilise water, kills bacteria
-
What are X-rays used for ?
-Let us see inside things
-diagnose broken bones
-airport scanners to detect hidden objects that can’t be detected with metal detectors
How does an xray work?
X-rays are transmitted by flesh and absorbed by denser material like bones or metal
To produce an X-ray image , X-ray radiation is directed through the object or body onto a detector. The brighter bits of an image are where fewer X-rays get through
What are gamma rays used for ?
-sterilising medical instruments as they kill microbes
-sterilise food as they kill microbes, keeping the food fresh for longer.
-some medical imagine techniques use gamma rays to detect cancer
-used in treatments of cancer
What happens when EM waves reach a boundary.
Absorbed
Transmitted
Refracted
Reflected
Are radio waves absorbed by the body?
Radio waves are transmitted through the body without being absorbed
How do microwaves travel through the body ?
Some wavelengths of microwaves are absorbed, heating the cells which may be dangerous
How does Infared and Visible light get through the body ?
Mostly reflected or absorbed by the skin, causing heating. Infared can cause burns if the skin gets too hot
How does ultraviolet get through the body? How’s it dangerous ?
Ultraviolet Absorbed by the skin. It has a higher frequency, so it’s potentially more dangerous. It’s a type of ionising radiation which can damage cells causing cancer.
How do gamma rays and X-rays get through the body?
What are they and what can they cause?
They pass through the skin and are absorbed by deeper tissues.
They are ionising so can lead to mutation and damage to cells(cancer).
What are all objects continually emitting and absorbing ?
All objects are continually emitting and absorbing EM radiation over a range of wavelengths
Distribution and intensity of wavelengths emitted and absorbed by an object depends on what?
The distribution and intensity of these wavelengths only depend on the objects temperature
What happens to the intensity of every emitted wavelength of an object when the temp of an object increases ?
As the temperature of an object increases, the intensity of every emitted wavelength increases
What will happen if the average power emitted by an object is greater than the average power it absorbs ?
If the average power emitted by an object is greater than the power it absorbs, temperature will fall.
What will happen to the objects temperature if the average power emitted by the object is less than the average power it absorbs ?
If the average power emitted by an object is less than the average power it absorbs, the temperature will fall
What must happen for an objects temperature to stay constant ?
For an objects temperature to stay constant, the average power it emits must be equal to the average power it absorbs
Graph to show peak wavelength decreases as temperature goes up…
How do EM waves from the sun get into and out of the earth
During the day lots of radiation is transfered to earth from sun
Some of this is reflected but most of it’s absorbed . This caused an increase in local temp
At night radiatiok is emitted by the atmosphere , clouds and earths surface
What must be equal for the earths temp to stay the same
Total absorption and total emittion
Practical to test what surfaces are better emitters ?
1) wrap 4 identical test tubes with material. Each material should have a different surface or be a different colour
2) boil water in a kettle then fill each test tube with the same volume of water
3)use a thermometer to measure the temp of the water in the test tube every minute. Seal the test tube tubes with bunds during the experiment
What you should find from the emitting glass test tube experiment …
matte surfaces are better emitters than shiny ones
black surfaces emit radiation better than white ones
How to investigate absorption using melting wax ?
1) stick two ball bearings to either side of the metal plate with solid pieces of candle wax. The other sides of these plates are then faced towards the flame. The plates are placed the same distance away from the flame
2) the side of the plates facing the flame have different colours, one is matte black and one is silver
3)the ball bearing on the black plate will fall first because the black surface absorbs more infared radiation- transferring more energy to the thermal energy store of the wax .
How to calculate wave speed using distance and time
Wave speed (m/s)= distance (m) / time (s)
How to calculate wave speed using frequency and wavelength
Wave speed = frequency (hz) / wavelength (m)
2 ways to find wave velocity ?
Wave velocity = frequency X wavelength
Wave velocity = distance / time
