Waves Flashcards
what are the types of waves
- tranverse
-longitudinal
what is a longitudinal wave
- a wave that oscillated side to side parallel to the direction of energy transfer
what are examples of longitudinal waves
- sound waves
- ultra sound waves
- p - waves
all longitudinal wave require a ——— to travel in eg air,liquid, solid
a medium
what does a longitudinal wave look like
has compressions and rarefactions
what is evidence that it is the wave that transfers energy for both longitudinal and transverse
what is a transverse wave
a wave that moves upwards and downwards and oscillates perpendicular to the direction of energy transfer
give examples of transverse waves
- ripples on the surface of water
- electromagnetic waves
- seismic s-waves
what are some differences between transverse and longitudinal waves
longitudinal waves: particles move parallel to the wave direction,BUT transverse waves particles move perpendicular to the wave.
- Longitudinal waves can travel through solids, liquids, and gases, while transverse waves typically travel through solids and on the surface of the liquids.
what is the wavelength of a wave
- the distance from a point on the wave to the equivalent point on the adjacent wave
what is the amplitude of a wave
the maximum displacement of a point on the wave away from it’s undisturbed position
what is the frequency of a wave
the number of waves passing a point each second
what is the period of a wave
the time taken for one wave to pass a point
how is the period measured
period (s) = 1/frequency(Hz)
what is the definition of wave speed
the speed at which the energy is transferred through the medium
describe a method to measure the speed of sound in air
- separate two people with a distance of 500 metres
- person A is holding the cymbals and person B is holding a timer
- person B will start timing when she sees person A clash the cymbals
-person B then stops the timer when she first hears the sound of the cymbals crashing - then calculate the speed of the sound waves by dividing the distance travelled / time taken
how is wave speed calculated
wave speed (m/s)= frequency ( Hz ) x wavelength (m)
what is the problems with the speed of sound experiment
- every person has a different reaction time ( it takes a fraction of a second to see the cymbals crash and press the timer )
BUT we can reduce the problem by having a large group of observers with timers - we can then collect their results and discard anomalies and calculate a mean
-second problem:
the time it tskes for the person to see the cymbals crash and hear the sound is very small
BUT to reduce this problem increase the distance between person A and person b ( the larger the distance the longer the time = makes it easier to start/stop the timer at the correct times
describe a method to measure the speed of ripples on a water surface. ( ripple tank. )
equipment :
need a tank ( ripple tank ) , water, a stopwatch and a ruler , vibrating bar - the vibrating bar is connected to a power pack
when the bar vibrates it produces waves on the surface of the water
above the ripple tank there is a lamp and below the tank is a white sheet of paper
when light shines through the water it produces the image of the waves on the paper
easiest way to obtain the data is by usnig phone as you can play back recording at different speeds or to freeze the image
how to measure the wavelength in the ripple experiment
place a ruler on the paper then. freeze the image of the waves - now measure the distance between one wave and ten waves further ( 10 wavelengths ) suppose the distance between the 1 wavelength and the 10th wavelength is 26cm (0.26m ) the value of one wavelength will be 0.026
how to calculate the frequency of the ripple tank experiment
place a timer next to the paper and count how many waves pass a point in one second - bit hard so it is more accurate to count the number of waves in 10 seconds and then divide it by 10 (. easier to record this on phone to watch in slow motion ) REMEMBER YOU NEED TO RECORD THE TIMER AS WELL AS THE WAVE
start the timer and calculate how many waves passed in 10 seconds divide your value by 10 to find the number of waves in 1 second
use the wave speed equation to determine the speed of the ripples
( multiply your value for frequency x wavelength ( 0.26 )
describe a method to measure the wavelength, frequency and speed of the waves in a solid
equipment :
string, wooden bridge, vibration generator, pulley on clamp, mass block, to signal generator
a string is attached on one end attached to a vibration generator - at the other end of the string there is a hanging mass ( the mass keeps the string taut ) - the vibration generator is attached to a signal generator - the signal generator allows us to change the frequency of the vibration of the string
when the power is turned on the string vibrates at a certain frequency a standing wave created due to resonance
now measure the wavelength of the standing wave to do that use a ruler - you need to calculate the total length of the standing wave from the wooden bridge to the vibration generator
using the wave speed equation and the value for the wavelength we can find the speed of the wave - wave speed = frequency x wavelength we read the frequency from the signal generator and the vlaue for the wavelength has already been calculate by using the ruler.
how do you calculate the wavelength of a standing wave
divide the total length by the number of half wavelengths and multiply by 2
what happens when a wave hits a boundary with a different material
- the wave can either be transmitted through the material ( will not change the wave )
what is rarefaction
what happens if a wave hits a boundary of a different material
- will either be transmitted ( wont change the wave )
- the energy of the wave is absorbed ( the wave wont pass through the material)
- wave may be reflected off the surface of material
describe how to investigate the reflection of light by different types of surfaces and the refraction of light by other substances
how do sound waves travel through a solid
- when sound waves move through the air the air particles vibrate ( and transfer kinetic energy through the material) side to side these vibrations move from one medium to another
what is the frequency of human hearing
20HZ - 20KHZ
which state do sound waves travel fastest in
solid
why do sound waves travel faster in solids instead of gases
because the particles in solids are closer to each other so the vibrations can pass more easily between them also sound waves travel faster is denser objevts
what happens to the frequency when a wave changes medium
the frequency doesn’t change
how does frequency change with pitch
high frequency = high pitch
low frequency = low pitch
how does amplitude chnage with pitch
high amplitude = loud sound
low amplitude = quiet sound
why can sound waves only travel through a medium
because sound waves move by particles vibrating
sound waves cannot pass through a vacuum as there are no particles
can sound waves be reflected
YES IT IS CALLED AN ECHO
what produces a sound wave
vibrations
which travels faster light or sound
light because it doesnt require a medium to travel through and can travel in a vacuum
what is ultrasound
a soundwave with a frequency higher than the upper limit of human hearing
how to ultrasound waves reflect at a boundary
partially reflects at the boundary between two different densities
what can ultrasound scanners produces
images of internal organs eg kidney and heart or images of a foetus
how can we determine how far a boundary is using ultrasound
The time taken for the reflections to reach a detector
are ultrasounds safer than x rays
YES
why are ultrasound waves safer than x rays
- ultrasound doesnt cause mutations and doesnt increase the risk of cancer
how is ultrasound use in industrial imaging
a flaw/crack creates a boundary inside a product. ultrasound waves are partially reflected from this boundary back to the transducer and then against the bottom of the product, which is shown on an oscilloscope
how are ultrasound used in prenatal scanning
ultrasound waves are partially reflected when they meet a boundary between two different media (different tissues in the body), and the wave returns to the transducer, arriving back at different times and creating an image
how do we hear sound
sound waves cause the ear drum, and other parts in the ear to vibrate which is picked up by nerve and gives the sensation of sound
what is the formula to determine the distance using ultrasound
distance = speed x time
how are seismic waves produced
earthquakes
how is the interior of the earth determined
- an earthquake happens due to sudden movement between tectonic plates in the earth’s crust = causing seismic waves which carry energy away from the earthquake, these seismic waves pass through the world and can be detected by seismometers , the patterns of these waves give us the information about the interior
what are the two types of seismic waves
- P WAVES
- S WAVES
what are p waves
- longitudinal waves
- waves that travel at different speeds through solids and liquids
what are differences between p waves and s waves
- p waves are longitudinal
- p waves travel at different speeds through solids and liquids
- p waves travel faster than s waves
- s waves are transverse waves
- s waves can only travel through solids
what are s waves
- transverse waves
- can only pass through solids
what type of paths do seismic waves travel in and why
curved paths because of density changes in the earth
what is the area where no s waves can be detected in
s - wave shadow zone - happens because s waves can’t pass through a liquid, this told scientists that the earth must contain a liquid core
why do p wave shadow zones occur
- because p waves travel faster in solids than in liquids = p waves slow down as they enter the liquid outer core , causing them to refract
what are electromagnetic waves
Electromagnetic waves are transverse waves that transfer energy from the source of the waves to an absorber.
what is the order of colours of light from long wavelength to short wavelength
RED ( LOW FREQUENCY) , ORANGE , YELLOW , GREEN , BLUE , INDIGO , VIOLET( HIGHER FREQUENCY)
order the electromagnetic waves from low frequency to high frequency
radio ( long wavelength ) , microwaves , infrared , visible light , ultraviolet , xrays, gamma rays ( short wavelength )
what wave from the electromagnetic spectrum is the only one that can be detected by human eye
visible light
what happens to the frequency from radio waves to gamma rays
increases
what happens to the wavelength from radio waves to gamma rays
decreases
how are the waves from the electromagnetic spectrum grouped by
grouped in terms of their wavelength and their frequency.
do electromagnetic waves need a medium to travel in
no they can travel through a vacuum
what type of speed do all electromagnetic waves travel in a vacuum
same speed ( 3x10^8 m/s)
how do waves change when moving from one medium to another
- change directions when they change speed
how does the velocity of wave change when moving from a less dense to more dense medium
slows down = causes the direction of waves to change ( bend towards the normal )
when waves slow down which direction do they bend
towards the normal
how does the velocity of wave change when moving from a more dense to less dense medium
the velocity increases and the wave bends away from the normal
when waves speed up which direction do they bend
away from normal
when does refraction happen
when any wave changes speed as it passes from one medium to another
what instance does refraction not happen
if the waves enter or leave the medium at right angles to the surface ( along the normal) then they dont change direction
what is the wavefront
an imaginary line that connects all the same points in a set of waves
why are wavefront useful
they make it easier to visualise lots of waves moving together
describe the required practical for determining infrared radiation
equipment: Leslie cube, shiny metallic surface, a white surface, a shiny black surface , matt black surface
- fill leslie’s cube with hot water
- point infrared detector at each of the 4 surfaces and record the amount of infrared emitted
IMPORTANT: keep the same distance between leslie’s cube and infrared detector as it makes the measurements repeatable
from the infrared investigation which surface had the most to least infrared emission
matt black, shiny black, white, shiny metallic
what can be used instead of an infrared detector
thermometer with bulb painted black BUT the resolution of the thermometer is less than the infrared detector = may not be able to detect a large difference between the surfaces using a thermometer unlike the infrared detector which will detect a difference
method to measure the absorbance of infrared by different surfaces
- use infrared heated and on either side there are two metal plates ( one plate is painted with shiny metallic paint and the other painted with matt black paint )
- on other side of plates vaseline is used to attach a drawing pin
- switch on heated and start timing
- the temperature of the metal plates increases as they absorb infrared
- record the time it takes for the vaseline to melt and the drawing pins to fall off
RESULTS:
the drawing pin falls of the matt black plate first , because matt black surface absorb more infrared than shiny metallic surfaces
what type of surface is best at emitting and absorbing infrared
matt black
what happens when electromagnetic waves are generated or absorbed
changes take place in atoms or in the nuclei of atoms
what happens when atoms are heated
electrons move from one energy level to a higher one , when the electron returns to its original level , it generates an electromagnetic wave
which EM waves can be harmful to humans
- ultraviolet, x rays , gamma rays
how are ultraviolet waves hazardous to the body
- causes skin to age prematurely and increases the risk of skin cancer
how are x rays and gamma rays hazardous to the body
- both are forms of ionising radiation that can cause mutation in genes and cancer
what does the damage caused by radiation depend on
- the type of radiation
- the dosage
what is the dose of radiation measured in
sieverts or millisieverts
how are radiowaves produced
radiowaves can be produced when electrons oscillate in electrical circuits these radio waves can be absorbed eg by an electrical circuit in an aerial , when this happens they now cause electrons in the circuit to oscillate which creates and alternating current with the same frequency as the radio waves
what are radio waves used for
transmit radio and tv signals
why are radio waves used
because they can travel long distances before being absorbed
as radio waves can reflect off a layer of charged particles in the ionosphere = allows us to send radio waves very long distances
what are microwaves used for
satellite communications, cooking food
how are microwaves used to heat foods
because most foods contains a lot of water molecules and water molecules absorb the energy of microwaves, the energy causes the food temperature of the food to increase
why are microwaves used for satellite communications
because microwaves can pass through the earth’s atmosphere without being reflected or refracted
what is infrared used for
electric heaters, cooking food, thermal-imaging cameras
what is the use of visible light
fibre optic communications, photography
what are optical fibres
thin strands of glass
why are optical fibres used
to carry telephone and cable tv signals
why can visible light carry lots of information
because it has a short wavelength
what are the uses of ultraviolet waves
energy efficient lamps, sun tanning
why does ultraviolet carry more energy than visible light
ultraviolet has a short wavelength
how does a bulb produce light
energy of ultraviolet is absorbed by the internal surface of the bulb is converted to visible light this requires much less energy than a normal light bulb
what are x rays and gamma rays used for
- medical imaging
- medical treatment
what can x rays do
visualise broken bones
what can gamma rays do
detect cancers
how can x rays and gamma rays pass through body tissue
because they’re both very penetrative
what is the focal length
The distance from the lens to the principal focus
which way does the light ray bend when it passes into the lens
towards the normal
which way does the light ray bend when it passes out the lens
away from the normal
what is specular reflections
Reflection from a smooth surface in a single direction and produces an image
what is diffuse reflection
Reflection from a rough surface causes scattering: but doesn’t produce an image
how do coloured filters work
by transmitting specific wavelengths of light and absorbing other wavelengths
how is the colour of an opaque object determined by
Wavelengths that are not reflected are absorbed. If all wavelengths are reflected equally the object appears white. If all wavelengths are absorbed the objects appears black.
why are opaque objects not clear
they don’t transmit any light
what are transparent objects clear
they transmit nearly all the light with only a small fraction that is absorbed or reflected
why are translucent objects half opaque and half clear
they only transmit some of the light
how are translucent objects determined
by which wavelengths are transmitted the most
what are primary colour filters
a filter that allows one of the three primary colours to be transmitted EG RED , GREEN , BLUE
what is shows for colour filters that arent for primary colours
let through the wavelength of the same colour as the filter
AND let through wavelengths of the primary colours that can be added together to make that colour
an objects colour depends on
- the wavelength of light absorbed by the object
- wavelengths of light hitting the object
- wavelengths of light reflecting off the object
what can all objects do in regards to infrared radiation
absorb and emit infrared object
what object will emit more infrared : a hotter objects or a cooler object
a hotter
what does the wavelength and intensity of radiation depend on
the temperature of an object
what happens to the quantity of infrared radiation emitted by an object as temperature increases
the hotter the object the more infrared radiation it will emit
what is a perfect black body
an object that absorbs all of the radiation that is incident upon it
how much radiation does a perfect black body reflect or transmit
none
How does increasing the temperature of an object affect its emissions
- the wavelength distribution of any emission is dependent on the object’s temperature
- the intensity of radiation emitted
why is a perfect black body the best possible emitter of radiation
- since it absorbs all radiation incident on it it will emit radiation well
what type of radiation do very hot objects emit in comparison to cooler objects
very hot: emit shorter wavelength radiation
cooler objects : emit longer wavelength radiation
how much will an object emit if the object is warmer than its surroundings
emit more than it absorbs so the temperature of the object will decrease
What will the rate of absorption and emission with an object with a constant temperature be
absorbing raditiation = same as emitting radiation
what are the ways that the earth can gain or lose energy
absrobing or emitting radiatino
what type of radiation does the sun emit
short wavelength radiation eg visible light an ultraviolet
give 2 factors that affect the temperature of the Earth
- the Earth’s rate of absorption and emission of radiation
- the amount of reflection of radiation into space
what can be said about the rates of emission and absorption for a body increasing in temperature
the body is absorbing radiation faster than emitting it
how does radiation affect the temperature of the Earth’s surface
- the sun emits short wavelength radiation eg visible light and ultraviolet
- this radiation travels to the earth
- some of that radiation is reflected eg by clouds
- remaining radiation can then be absorbed by the surface of the earth = causes the temperature of the earth to increase
- earth now emits infrared radiation back into space
how can some energy of infrared be trapped
by greenhouse gases in the atmosphere eg carbon dioxide
how does human activity affect the atmosphere
- Increases the level of greenhouse gases = more heat energy is trapped in the atmosphere and less is radiated into space
what is a factors that can affect how much energy is radiated from the earth
- the amount of cloud cover
cloudy nights are —— than clear night
warmer
why are cloudy nights warmer than clear nights
because the clouds can reflect infrared back to the earth and prevent it from being radiated into space
