TOPIC 2- Waves and the Electromagnetic Spectrum Flashcards
Wavelength
(Lambda)
Peak to peak measurement of length of a wave cycle.
(M)
Amplitude
Displacement from rest position to a crest/trough. (M)
Frequency
The number of complete cycles of the wave passing a certain point per second. (Hertz)
Time period
The time it takes for a wave to carry out one complete oscillation. (S)
1/frequency
Wave speed
Frequency * wavelength
(Lambda)*frequency
Transverse waves
Waves where particles oscillate perpendicular to the direction it’s travelling.
Waves
The transfer of energy and information in the direction that they are travelling.
What happens when waves travel through a medium?
Particles of the medium vibrate and transfer energy/information between each other while particles overall stay in the same place.
Transverse waves
Waves where vibrations are perpendicular to the direction the wave travels. Most waves are.
What type of wave are EM waves?
Transverse
What type of waves are S waves?
Transverse
What types of waves are water ripples?
Transverse
Longitudinal waves
Vibrations are parallel to the direction the wave travels.
Examples of longitudinal waves
Sound waves
P waves
Compressions
High pressure squashes w lots ofparticles
Rarefactions
Low pressure stretches w fewer particles
Wave speed=
Distance/time
Frequency*wavelength
How do you measure the speed of sound?
Attaching a signal generator to a speaker at a specific frequency.
2 microphones and an oscilloscope help to find wavelength of the sound waves generated..
1 start w both microphones next to speaker and slowly move one away until waves on oscilloscope align but moved 1 wavelength apart.
The distance is the wavelength
How do you measure the speed of water ripples
Use signal generator attached to a dipper of a ripple tank, creating waves at a set frequency. Dim lights and turn on strobe light to see wave pattern. Alter strobe light so wave pattern appears to freeze and so stop moving (frequency of waves and strobe light are equal).
Distance between each shadow= one wavelength
How do you find the speed of waves in solids
1 measure and record length of a metal rod
2 attach w elastic bands so hangs w clamps next to microphone.
3tap rod w object and write down peak frequency displayed by computer,
4 repeat *3 to get an average
5 wavelength = twice length of rod
What three things can happen when a wave meets a boundary?
Absorption
Transmission
Reflection
ABSORPTION of waves at boundaries
Wave transfers energy to material’s energy stores, often thermal which leads to heating.
TRANSMISSION at wave boundaries
Wave carries on travelling through new material, often leading to refraction.
Can be used in communications as well as in glasses/camera lenses.
REFLECTION of a wave at a boundary.
Oncoming wave is sent back away from second material.
How echoes are created.
Refraction
When waves change direction at a wave boundary due to the changing speed caused when a wave crosses a boundary (of materials w different densities) at an angle which causes a change in direction.
(Greater speed change = greater change in direction)
Which direction does a wave bend if it slows down?
Towards the normal
Which direction does a wave bend if it speeds up?
Away from the normal
TAGAGA
What happens to the speed of EM waves in denser objects?
They slow down
How does wavelength affect EM wave refraction?
Shorter wavelengths bend more than longer wavelengths.
Dispersion
Wavelengths spreading out.
What happens to the frequency of a wave as it crosses a boundary ?
It stays the same.
V = (lambda)*f
What happens to the wavelength when a wave slows down?
Speeds up?
It decreases
Increases
How do you draw a ray diagram?
Draw boundary between 2 materials and the normal (at 90° to the boundary).
Draw an incident ray (meeting normal at boundary)
Draw refracted ray (meeting normal at boundary)
Angle of incidence
Angle between the incident ray and normal
Angle of refraction
Angle between refracted ray and normal.
Sound waves
A type of longitudinal wave caused by vibrating objects and composed of a series of compressions and rarefactions.
How does a sound wave travel through a solid?
Causes particles in the solid to vibrate.
Which aspects of an object determine which frequencies it can transmit?
Size
Shape
Structure
How does a speaker produce sound waves ?
An electrical signal causes a paper diaphragm in it to vibrate back and forth, causing surrounding air particles to vibrate. Travels through air as series of compressions and rarefactions.
What surfaces reflect sound waves?
Hard and flat surfaces
Why can’t sound travel in space?
Is a vacuum so there are no air particles to move or vibrate.
How do you ear?
Your eardrum vibrates, passing vibrations on to ossicles through to the semicircular canals and to the cochlea, which converts the vibrations to electrical signals which are then sent to your brain. The brain interprets signals as sounds of different pitches and volumes, depending on frequency and intensity.
What’s human hearing limited by?
Size and shape of the eardrum as well as the structure of all the parts of the ear that vibrate.
Ultrasound
Sound with frequencies higher than 20,000 hertz.
What happens to ultrasound waves when they hit boundaries?
They are partially reflected. This means that some is reflected off the boundary and some is transmitted (and refracted).
How do you detect objects with ultrasound?
Pointing a pulse of ultrasound reflects back when it hits a boundary. Time taken to reach a detector can be used to measure how far away the boundary is.
How can ultrasound be used?
Medical imaging
Industrial imaging
Medical imaging
Ultrasound waves pass through body but are reflected when they hit 2 different media and then detected. Timing and distribution of echoes are processed by computer to produce video image.
Completely safe.
Industrial imaging
Ultrasound reflects on far side of material, if there’s a flaw then waves will be reflected sooner.
Echo sounding
Sonar used in boats/submarines to find distance to seabed/location of objects underwater.
Infrasound
Sound waves w frequency lower than 20 Hz.
How are infrasound waves used for conservation?
Scientists can track animals that communicate via ultrasound.
How is ultrasound used when predicting events?
Natural events (eg, volcanoes, avalanches and earthquakes) produce infrasound in area. Monitoring of this allows prediction of events.
How do you detect seismic waves?
Seismometers used by seismologists working out time taken for waves to reach seismometer and note which part of earth don’t receive seismic waves.
What happens when seismic waves meet a boundary?
Some waves will be absorbed and others refracted. If refracted, change speed gradually, resulting in curved path. Property change causes an abrupt change in speed and so a kink in the path.
2 types of seismic waves
P-waves
S-waves
P waves
Longitudinal waves that pass through solids/liquids.
Faster than S waves
S waves
Transverse waves that only travel through solids. Slower than P-waves.
Law of reflection
Angle of incidence= angle of reflection
Angle of reflection
Angle between reflected wave and normal.
Normal
Line perpendicular to the surface at point of incidence shown as a dotted line.
Total internal reflection
When the wave travels through a dense material towards a less dense substance like air, the angle of incidence is larger than the critical angle for that particular material.
Speculation reflection
When waves are reflected in a single direction by a smooth surface, creating a clear reflection.
Diffuse reflection
When waves are reflected by a rough surface so they are reflected in all directions. Creates matt surface.
How do you investigate refraction?
- ) trace around rectangular glass block on a piece of paper, shining thin ray of light from a ray box onto middle of one side.
- )trace incident/emergent ray, remove block and draw straight line to join up incident and emergent ray (demonstrates path of refracted ray through the block).
- ) draw normal at point where light ray entered the block, use protractor to measure angle between refracted ray and normal (repeat w emergent ray)
- ) repeat*3 and calculate average for angles.
Opaque objects
Objects that do not transmit light.
When visible light hits, they absorb some wavelengths of light and reflect others.
How are objects white?
Reflect all wavelengths of visible light equally.
How are objects black?
They absorb all wavelengths of visible light.
Transparent/ translucent objects
Objects that transmit visible light or allow some to pass through.
Colour filters use
Filter out different wavelengths of light, so that only certain colours are transmitted and rest are absorbed.
Filters that aren’t made for primary colours
Let through both wavelengths of light corresponding to the colour.
How do lenses form images?
By refracting light and changing its direction.
2 main types of lens
Converging
Diverging
Converging lens (convex)
Bulges outwards in middle.
Causes parallel rays of light to be brought together (converge) at principal focus.
Diverging lens (concave)
Caves inwards.
Causes parallel rays of light to diverge.
Axis of a lens
Line passing through middle of a lens
Principal focus of converging lens
Where parallel rays meet
Principal focus of diverging lens
Where parallel lines appear to come from.
Focal length
Distance from centre of lens to principal focus.
Where are images formed on lenses ?
Where all light rays from a certain point on an object appear to come together.
2 main types of image
REAL IMAGE (when light rays actually come together to form image) VIRTUAL IMAGE (when light rays from an object appear to be coming from a completely different place to where they are actually coming from.
How does power affect focal length?
Stronger = shorter focal length
Power on converging lens
Positive
Power on diverging lens
Negative
How does curvature affect power?
More curved= more powerful
How do draw a ray diagram for a diverging lens?
- ) draw ray from top of object parallel to the axis of the lens.
- )draw another ray from the top through to the middle of the lens
- )the parallel incident ray is refracted so appears to come from principal focus (dotted line before reaches lens)
- ) the ray passing though the middle never bends
- ) mark where the dotted virtual ray meets the middle ray
- ) repeat for a point on the bottom of the object.
What’s the virtual image produced by a diverging lens?
The right way up, smaller than the object and on the same side of the len as the object.
How do you draw a ray diagram for an image through a converging lens?
- ) draw ray from top of object parallel to lens axis. Draw another from top through middle of lens.
- )parallel incident ray is refracted through principal focus, draw refracted ray through F. Middle ray doesn’t bend.
- ) where rays meet is top of image (mark it).
- ) repeat for bottom of object.
How does distance from the lens affect the size and position of the image?
Object nearer than F (1 focal length) will produce right way up, bigger virtual image on same side of lens.
Object further than F but smaller than 2F will make real, inverted, bigger object beyond 2F.
Object further than 2F produces real, inverted, image same size and at 2 F on other side of lens.
Electromagnetic waves
Transverse waves that all travel at the same speed through a vacuum, however at different speeds through materials (can lead to refraction/dispersion).
EM wavelengths
Vary from 10 to the -15 meters to 10 to the 4 meters.
How are EM waves grouped?
According to their wavelength and frequency (7 basic types that can merge to form a continuous spectrum)
How are EM waves generated?
Via a variety of changes in atoms and their nuclei, giving a large range of frequencies.
What type of EM wave can the human eye detect? Acronym for this?
Visible light which can be split into different colours w different wavelengths.
Richard Of York Gave Battle In Vain
Red Orange Yellow Green Blue Indigo Violet
Order of EM waves.
How are they grouped?
Radio waves (longest wavelength and lowest frequency)
Microwaves
Infrared radiation
Visible light
Ultraviolet
X-rays
Gamma rays (shortest wavelength and highest frequency)
Where do EM waves transfer energy from and to?
From a source to an absorber
How does frequency affect how much energy it transfers?
How does this affect people?
Higher frequency = more energy
Can be dangerous for humans.
Radio waves effects on humans
Transmitted through body without being absorbed
Microwaves implications on humans
Some wavelengths of microwaves can cause heating of cells (can be dangerous)
Infrared/ visible light implications on humans
Mostly reflected/absorbed, causing some heating.
IR can cause burns if skin gets too hot.
Ultraviolet implications on humans
Absorbed by skin, w higher frequency.
IONISING radiation so can cause damage to cells on surface of skin (leading to skin cancer)
Can damage eyes (blindness)
Xrays / gamma rays implications on humans
IONISING so can cause mutations and damage to cells.
V high frequency so transfer much energy and so more damage, passing through skin to be absorbed by deeper tissues.
What does the distribution and intensity of EM wavelengths depend on?
The object’s temperature
Intensity
Power per unit area
Power
Energy transferred per second
What happens as temperature of an object emitting waves increases?
The intensity of every emitted wavelength increases.
How does wavelength affect how quickly intensity changes?
Intensity increases more rapidly w shorter wavelengths than longer wavelengths, meaning peak wavelength decreases.
How does the rate at which an object absorbs/radiates EM radiation affect its temperature?
If average power of the object’s absorption is more than the power it radiates, the object heats up.
If average power of absorption is less than the power it radiates, the object cools down.
An object at a constant temperature radiates and absorbs at the same average power.
How does the earth’s temp depend on radiation?
Sun transfers radiation to earth, some reflected and most absorbed by atmosphere, clouds and surface, causing an increase in local temp, which stays fairly constant.
Changes to atmosphere can change earth temp.
How do you investigate how well different surfaces emit radiation?
1.) wrap 4 identical testubes w material. This material should be same w different surfaces/colours.
2.) fill each test tube W same volume of boiled water.
3.) use thermometer to measure temp in tubes every minute, sealing w a hung between each one.
Quicker decrease in temp = better emitter of radiation
What are alternating currents made up of?
Oscillating charges that produce oscillating electric and magnetic fields.
How are radiowaves produced?
Using an alternating current in an electrical circuit.
Transmitter
Object in which charges oscillate to create radio waves.
Receiver
The object that absorbs transmitted radio waves
How energy is carried by radiowaves to the receiver
Transferred energy causes the electrons to oscillate and generates an alternating current in the electrical circuit of the receiver. Which has same frequency as radiowave that generated it.
How are radiowaves used in communication ?
LONG-WAVE RADIO (w wavelengths of 1-10km) bend around curved surface of earth so radio signals can be received if receiver isn’t within straight line of sight of transmitter. SHORTWAVE RADIO (10m-100m wavelengths) can be received at life no distances from transmitter as are reflected by earth’s atmosphere. BLUETOOTH use short wave to send data over short distances between devices. TV/FM RADIO (v short wavelengths ) must be in direct sight of transmitter as signal doesn’t bend/travel through buildings.
Which EM waves do satellites use?
Usually microwaves that can pass through earth’s atmosphere but can be high frequency radio waves too.
Satellite TV transmitter transmit signal into space which are picked up by satellite receiver dish orbiting far above above earth which transmits signal back to earth in different direction so is received by satellite dish.
Uses of microwaves
Communications (microwaves can pass through earth’s atmosphere) Microwave ovens (obvs at different wavelength to satellites as penetrates few cm into food to transfer energy to water molecules in food so heat up and transfer energy to rest of food molecules to quickly cook it)
Infrared uses
Infrared cameras (detect IR radiation and so monitor temperature, turns into electrical signal to be displayed on screen as thermal imaging) Thermal imaging (used by police to see suspects in dark) Infrared sensors (security systems set off alarm) Toaster (transfer heat to bread) Electric heater (emits IR to be absorbed by objects/air in room ) Information transfer (files between phones at small distances) Tv remote Optical fibres (carry data over long distances via pulses of IR in a single wavelength to prevent dispersion using total internal reflection.
Uses of visible light
Lights (obvs) Photographic film (reacts to light to form image) Cameras (image sensors detect visible light and generate electrical signal which is converted to an image which can be stored digitally or printed)
Uses of ultraviolet
Fluorescent lights (emit visible light w UV, are energy efficient ) Security pens (identification of stolen property) Bank notes/passports Water sterilisation (kills bacteria in water so is safe to drink)
Uses of x-rays
Viewing of internal structures of objects and materials.
Affect Photographic film
Diagnosis of broken bones (transmitted through flesh but absorbed by bones, directed onto detector plate w brighter (negative) areas of fewer x rays)
Security scanners detect hidden objects better than metal detectors
Uses of gamma rays
Sterilise medical instruments and food, allowing food to stay fresh for longer (safe) Medical imaging use tracers to detect cancer Cancer treatment (radiation targeted at cancer cells to kill them)
