Section 2 - Waves and The Electromagnetic Spectrum Flashcards
What do waves transfer?
energy and information in the direction they are travelling
What is the amplitude of a wave?
The displacment from the rest position to a crest or trough
What is the wavelength of a wave?
length of afull cycle of a wave ( crest to crest )
What is the frequency of a wave?
the number of complete cycles of wave passing a cartain point per second
Mesured in Hz
What is the period of a wave?
the number of seconds it takes for one full cycle
What way do transverse waves vibrate?
Sideways, the vibrations are at 90degrees to the direction of the wave travel
What are some examples of transverse waves?
All electro magnetic waves
S waves
ripples and waves in water
what way do longitudinal waves vibrate?
parralel vibrations to the direction of the wave travel
They extend and compress
What are some examples of longitudal waves?
sound waves
P waves
What 3 things can happen to waves at boundaries?
Absorbed
Transmitted
Reflected
Wave ABSORBED
the wave transfers energy to the materials energy stores
Wave TRANSMITTED
the wave carries on travellign throughthe new material. This often leads to refraction
Wave REFLECTED
the incoming ray is neither absorbed or transmitted but instead is sent back “away” from the second material
Echos
What is Ultrasound?
sound with frequncies higher than 20,000Hz.
What happens to Ultrasound waves at boundaries?
They get partially reflected at boundaries ( some of the wave is reflected off )
What are some usefull ways to use Ultrasound? Why?
Pre-natal scanning of foetus
Industrial imaging
this is because when ultrasound reaches a medium boundary it is partially reflected. This reflection can be processed into a scan.
what is Infrasound?
Sound with frequencies lower than 20hz
What are some examples of Infrasound?
Whales and ELephants use it so communicate, this can be picked up and used to track these animals
Infraosund (seismic waves ) is released before an earthquake so scientists can pedict when the earthquak is going to happen
What are the two examples of Seismic waves?
P waves and S waves
P waves
They are LONGITUDINAL
they travel through solids and liquids
They travle faster than S waves
S waves
TRANSVERSE
onyl travle through solids
they are slower than P waves
What is the total intertial reflection
at what angle all of the wave is reflected
- Only happens when going from dense -> less dense material.
transparent vs translucent
When going through a transparent matter, the light rays stay parralel to eachother. Whereas when going through a translucent matter, the waves are scattered ( this means you cant see a clear image
When from a fast object to a slow one…
Light refracts towards the normal
When from a slow object to a fast one…
light refracts away from the normal
what is white light?
a mixture of all the different colours of light
What do opaque object do?
they do not transmit light.
They absorb some wavelengths of light and reflect others
Why do opaque objects have color?
They absorb some wavelengths of light, and refect other wavelengths, the wavelenghts corresponging to the visible spectrum reflected are the color the object is.
Transmit
to pass through
What do white objects do?
Reflect all wavelengths of visible light equally
What do black objects do?
absorb all wavelenths of visible light
- are a lack of visible light
Transparent
See through
translucent
partially see through
What do transparent and translucent objects do?
Transmit light - they appear as the color they most strongly transmit
Color filters
only let particular wavelenths through
- used to filter out different wavelengths of light, and therefore onyl let certain ones through
- if a color is not transmitted through the filter the object will appear black
EM waves
- spectrum grouped on wavelength and frequency
- transverse
- all travel at the same speed in a vacuum but travel at different speeds in different materials
- Vary in wavelength
- eyes can only see the visible light
- transfer energy from a source to an absorber
- Higher frequency = more energy
What are the three sections of the EM spectrum with long wavelengths?
Radio waves
Micro waves
Infrared
What are the three sections of the EM spectrum with short wavelengths?
Ultra violet
X rays
Gamma rays
Radio wave - Heath implications
transmitted throught he body without being absorbed- safe
Micro wave - Heath implications
Some wavelengths can be absorbed, causing heating of cells - may be dangerous
Infrared and Visible light - Heath implications
Mostly reflected or absorbed by skin, causing some heating. IR can burn
Ultra Violet- Heath implications
Absorbed by skin but because it is a higher frequency is more dangerous.
- ionising radiation - when absorbed an cause damage to cells on the surface of skin -> can lead to cancer
- can damage your eyes - eye conditions and blindness
X rays and Gamma rays- Heath implications
- Ionising radiation - can cause mutations and damages to cells -> cancer
- High frequency - high damage
- can pass through skin and be absorbed by deeper tissues
What is the order of the EM spectrum
Radio waves
Micro waves
Infrared
Visible light
Ultra Violet
X rays
Gamma rays
Power
energy transferred per second
mesured in W
Intensity
Power per unit area
Visible light - uses
Light bulbs are designed to emit it
Cameras detect it and use it to capture images
Infrared - uses
- Communication at short distances
- Optical fibres
- Grills or toasters uses them to heat things up
- thermal imaging -> Security systems
Microwaves - uses
- Communications ( mobile phone signals )and sattelite transmittions
- Microwave oven - heating food
Radiowaves - uses
- transmitting radio broadcasts ( sattelites)
- ground -> spacecraft
how are Radiowaves produced
Produced by oscillating currents in electrical circuits - also can cause these
Oscillate
go back and forwards
Oscillating currents
Electrons moving backwards and forwards
What path do waves travel in?
Straight lines unless reflected or refracted
Refraction
the bending of a path due to a change in velocity
The Ionosphere
The top part of the atmosphere
Some radiowaves and all microwaves pass through it
- if radiowaves reach the ionosphere at a suitible angle, they can be refracted back, allowing further travel.
radiation and temperature
The intensity of radiation emitted by an object increases as it temperatures increases, the wavelengths also change with temp - Higher temp = more energy = shorter wavelength
Radiate
emit
energy coming out of stuff
absorb
energy coming into stuff
Cold
absence of heat energy
colder things will absorb more heat
How can something stay at a constant temperature?
It must absorb the same amount of heat energy it radiates
- Heat will spread from high temp to low temp untill a thermal equilibrium is reached
The earths energy balance
- absorbs about 1/2 the radiation t recves from the sun
- radiates it as infrared
The greenhouse effect
Some gases in our atmosphere ( mainly CO2 ) naturally abosrb some energy, keeping the earth at a higher temperature than if there were no atmosphere
Specular
Waves are reflected in a single direction by a smooth surface - clear reflection
Diffuse
Waves reflected by a rough surface are reflected in all directions - matt, no reflection
Ultra-violet uses
Flourescent lamps
Sterilise water - kills bacteria
X-rays uses
for x-ray images in hospitals or airport security scanners
Gamma rays uses
Sterilise medical instruments - kill microbes
Cancer scanning or treatments
What us ultrasound and its uses?
Sound with frequencies higher than 20 000 Hz
- Foetal scanning
- Industrial imaging
What is infrasound?
Sounds with frequencies lower than 20hz
- Some animals such as whales use this to communicate
What EM has the highest frequency?
Gamma
What EM has the highest wavelength?
Radiowaves
Does Wave speed change throughout the EM spectrum in a vaccum?
no
How do you calculate Wave speed?
Distance/Time
or
Wavelength x frequency
What do you use to mesure the speed of sound?
Oscilloscope
Explain the practical to mesure the speed of sound
Attach a signal generator to a speaker so it can release sound waves with specific frequencys
1. Set up an Oscilloscope attached to two microphones so the waves from each microphone are seperate
2. Start with both microphones next to the speaker, then slowly move one away untill the two waves are aligned, but one is exactly one wavelength apart
3. Mesure the distance between the microphones to find one wavelength
4. Then use v = fλ fo find the wavespeed, th frequency is whatever you set the speaker to
Explain the experiment to mesure the speed of water ripples using a strobe light
(Liquids only)
- Using a signal generator attached to the dipper of the water tank, create water waves at set frequency
- Dim the lights and turn on the strobe light to see a wave pattern made by the shadows of the crests of the waves
- Alter the strobe light’s frequency untill the wave pattern appears to stop moving - this is when the frequency of the wave is the same as the strobes ( lit at same point in cycle each time)
- Mesure wavelength (Dist between shadows) and find average of 10
- Use v = fλ to find the wavespeed
Find frequency by calc waves passed a point in a set time (normal light)
Describe the THEORY behind the experiment using peak frequency to find the speed of waves in solids
(for solids)
Can do this by mesuring the frequency of sound waves when you hit an object e.g a rod with a hammer. Hitting the rod causes waves to be produced along the rod. These waves make the rod vibrate and produce sound waves in the air around the rod. These sound waves have the same frequencies as the waves in the rod
Describe the experiment using peak frequency to find the speed of waves in solids
1) Mesure and record the length of a rod
2) Set up clamps to hold elastic bands, holding up the rod, put a microphone at the end of the rod (leading to computer)
3) Tap the rod (other side of rod than microphone) with the hammer. Write down peak frequency displayed by the computer
4) do this X3 to get peak average frequency
5) Calc speed with v = fλ (λ is x2 length of rod)
What happens when a wave hits a boundary of a different material
(not along the normal)
Different material density -> change in speed -> change in direction
This is called Refraction
What happens when a wave hits a boundary of a different material along the normal
It will change speed but it is not refracted
What happens at a boundary when there is a greater change in speed?
this causes a greater change in direction
What happens to the speed of EM waves when they travel in denser materials?
they slow down
How is an EM wave’s refraction affected by its wavelength?
Shorter wavelengths bend more
(this is why white light can refract into a spectrum)
What happens to the frequency of a wave as it crosses a boundary, relating to v=fλ?
It stays the same, because there is a change in speed and v = fλ, this means that wavelength changes
How does wavelength behave in a boundary when slowing down or speeding up?
Slowing down = λ decreases
Speeding up = λ increases
How does the speed of sound change in different states
gases<liquids<Solids
- they can refract
- Will be reflected by hard, flat surfaces
- cant travel in a vacuum (no particles to vibrate)
Frequency doesnt change
