phys section 2 waves and their effects

what effect do waves have on matter

waves do not transfe matter from one place to another, they can make matter oscillate up and down or side to side but there is no net travel

what is ionisation

wen radiaotn hits an atom or molecules and it hs enough energy to remove an electron and change the atom or moleules the changed atom is charges and called an ion

what problems cn IR radiaiton cause or hmans why

when skin is exposed to IR radiiton it heats up because IR radiaiton from sources lke th fire an sun ccause heating nd too much IR radiaiton can burn the skin

how can you refect white light

with a prism to make a rainbow ifferent wavelengths of light refract by different amounts so white light disperses into different colours as it enters a prism a rectangular block has parallel boundaries so the rays bend by the same amount hen thwy leave the block as when they entered so the rays emerge parallel with a triangular prism, the bounaries are not parallel so the different wavelengths do not emerge parallel and you get a rainbow effect

can radiowaves be receved at long distances

yes short wave radio signal (10m - 100m) not long radio signals can be received at long distances from the transmitter because they are reflected from the ionosphere (an electrically charge layer in the earths upper atmospher0 - medium wave signals can also reflect from the ionosphere depnding on atmospheric condtions and the time of day

can douns wves reflect and refract

yes sound wves are reflected y hard surfaces and refract as they enter different media as they enter a denser media they speed up becase because sound waves spread out so much the change in diection is hard to spot under nrmal circumstances the reflection isnoticeable in an room becuaes a big room sounds ifferent once you put a carpet and curtains in because these things absorb the sound quickly and stop it from echoing around the room echos ae eflected sound waves there i a delay between the original sound and the echo because the echoed sound waves have further to travel and so take longer to reach your ears

what is the frequency of a wave

, the nuber of complete waves passing a certain poing per second or the number of waves produced by a source each second measures in HZ , 1Hz is 1 wave persecodn`

how can IR be used to monitor temp

- IR radiation is given out by hot bjects, themore thehotter - heat loss through houses uninsulated roof and security systems that detect body heat can be detected using IR sensors used in night vision equipments because the equpment turns it into an electrical signal which is displayed on a screen s a picture the hott er an object tebrighter it appears polic and milatry use this to spto suspecs automatic doors also detect bod heat

why can you sometimes not get reception for TV and FM signals if radio waves can diffract

- TV and FM radio transmissions have very short wavelengths (10cm-10m) so to get reception you must be in direct sight of the transmitter because the signal does not bend around hills of travel far through buildings

what are sound waves

- cause by vibrating objects - these mechanical vibrations are passed though the surounding medium as a series of compressions and they are type of longitudinal waves

what happens if you sepdn too much time in the um

- get tanned or sunburnt - increase chance of getting skin cancer beause the suns rys include ultraviolet radiation which damages the DNA in cels - UV radaiton can also cause eye problems e.g. cataracts and premature skin ageing

how do sound waves have different pitches

- high freq sound waves sound high pitched like a squeakingnoise - low frequency sound waves sound low pitched like a mooing cow - high frequency/pitch also means shorter wavelength

uses of x rays

- radiographes in hospita used to take X ray photgraphs of people to ses if they have broken bones x rays pass through flesh easily but not through denser material e.g. bones or metall so it is the amount of radiaiton that is absorbed that gives the ray iage the brighter bits are where fewer x rays get rhough this is a negativ e image, the plate starts off all white - x rays caus cancer so radiogrpaher wear lea aprons an stand behind lead screen or leave the oom to minimise exposure airport security use x rays to scan luggage to check for suspicious looking objects - airports not use x ray scanners on passengers to llok for concealed weapons or exposives low level x rays are used so they are not as harmful as the x rays used in hospitals

what can you say about the spped, wavelength and freq of a wave

- speed of a wave is usually independent of the freq and amplitutde of the wave - the freq of a wave is set at ts source - spped and wavelenth cn vary depending on the medium the wave is travelling through

when do we hear sounds

- when sound vibrations travel through someones each and reach ear drums

how can you see water waves refracted

-wait until surface of waer is flat drop pebble in water near to flat side of container - circular ripples ofwater waves travel out from the point the pebble hit the water - when the ipples rech the flat side f the conainer they are reflected and you can see part circle ripples which appear to come from he wall

what cause the green hous effect how

IR radiaiton - EM radiaiton frm the sun can pass through the Earth's atmosphee to heat up the surface - when the radiaiton is emitted back from the surface it is at a lower freq - IR radiaiton - lotsof the IR is absorbed by atmospheric gases called green house gases including carbon dioxide, methan and water vapor - these gases reradiate heat in all directions including back towards the earth so the atmosphere acts as an insulating layer stopping the earth losing all its heat at night - this is called the geenhouse effect because in a greenhous when the sun shines, the glass helps keep some of the heat in - without the greenhose gases in the atmosphere e.g. CO2, methane, water vapour the earth would be a lot colder than itis but too much greenhouse fas could lead to global warming

what is fluorescence

a property of certain chemicals where UV is absorbed and visible light is emitted this is why fluorescent colours look so bright because they do emit light

what is the law of reflection

applies to every reflected ray

how do remote controls work

by infrared waves in waireless remote controls they emit different patterns of infrared waves to send different commands to an appliance

what happens when a wave crosses a boundary between to substances a) head on b) at an angle

changes speed

what does refction change about light ways

changes the direction but no the speed, wavelengh or freq

what are the uses in homes form IR radiaiton

cooking in grills and toasters used to transmit information between moble phones or computers but only over short distnces in remote controls and opitcal fibres

descrbe transverse waves give exmaples

e.g. light E waves sliky sping wiggled up and down, waves on strings s waves seismic waves the vibratiosn are perpendicular to the direciton of energy transfer of the wave

give examples and decription of longitudinal waves

e.g. sound waves, ultrasound waves slinky spring when you push the ens P waves seismic waves

how can infra or ultra sound be generated

electrical deices produce electrical oscillations of any frequencies and these can be converted into mecanical vibrations to produce sound wavesbyond the range of human hearing

what do radioactive material do

emit ionising gama radiaon all the time

what else is a problem apart from exposure to the sun

exposure to sunbed in tanning salonds so there ae tiem limits to prevent overexposure

where does sound travel fastest

fastests in solids than in liquids ad faster in liquids than in gases cannot travel in space because it is mostly an vacuum and there are no particles to vibrate

what type of radiaont is more harmfl

hig energy EM radiaiton e.g. x rays and gamma rays and UV caus emore harm than low energy e.e.g radio waves because it takes a lot of energy to remove an eletron from an atom or molecules so only radiaitonwith high eneough energy can caus eioniation

uses f gamma rays

high does used to trat cancer - to diagnose cancer if a radioactive isoope is injected into the patient and a gamma camera is then used to detect where the radioactvie isotope travels in the body this creats an image which can then beused to detect where they might be ancer

how does photography work

in a similr way to the eye cameras use a lens to focuse visible light onto a light sensitive ilm or electronic sensore that records images the lens aperture controls how much light enters the camera like the pupil in an eye the shutterspped dtermines how long the film or sensor is exposed to light by carying the aperturre and shutter speed and the senstivity of the film or the sensor an photographer can capture as much or as little light as they want

what appens when light enters the eye

it gets refracted through the lens and focused onto the retina at the back of the eye the retina sends messages to thebrain via th optic nerve and the brain interprets them

main type of wave not transverse

logitudinal

wavelength of radiowaves

longr than 10cm

are ther health risks of usig mobile phoen

maybe a phone emits micowave radiation if some of the radiaiton is absorbed by thebody and caue heating of the body tisues whic contain water and cells could be bruned or killed some people think that microwaves emited into body from a phone or living near a mobile phone mast could damage your health there is no oncluive proof either way tudie have given conflicting evidence

whattype of waves are water waves and waves in sprins and ropes

mechanical waves

waves travel at different spedds in...

mediums with different optical densities

how to microwave ovens work

microwaes need to be absrobed by water moleules in food to heatit up so they use a different wavelength to those ued in satellite communications - th microwaves penetrate up to a few cm into the food before ebing absorbed by water molecules. the energy from the absorbed microwwave casue the food to hat up the heat energy is then conducted or convected o other part of the food

do microwave ovens use the same wavelength as waves from satellites

no

do EM waves ae the same propertes

no, EM waves with different wavelengths or freq have different roperties

are te types of EM waves completely sepaate

no, the different regiosn merge to form a continuous spectrum

what is optical densitynt the same as

not the same as mass denistywaves travel at different spedds in...

how can you demonstrate the bending effect of refraction

objects look bent when placed in water if you put something straight e.g. pen and partially submerge it int water th bottom part will look slightly biger and the edges will not quite meet up with the pencil edges out of the water becuase the light fro mthe pencil is refracted by the different boundaries before it reaches the eyes

what allows us to ee ojects

reflection of light light bounces ooff the objects into our eyes

how do the police use UV radiation

security pens are use to mar properties with names e.g. aptops and the ink in the pen is only viible in UV light and this cna help the police identify your property if it is stolen

what is ultra sound

sound that has a frequency about the range of human hearing 20,000Hz used for prenatal scanning and sonar

what is infrasound

sound that is too low for humans to hear below 20Hz

how to calculat spped of a wve

speed=distance over time

what does SPF mean

sun protection factor an SPF of 15 means you can spend 15 times longer in the sun without burning

what detemines the loudness of the sound wave

the amplitude the bigger te amplitude, the louder the sound

why do microwaves have metal cases an creens ver the glass dooe

the cases and screens reflect and aborb the mirowaves and stop them from gettng out so that the microwave radiation would heat up the water in your bodys cells if you were exposed to it

why is ionisation bad for cells

the cells contani important molecules e.g.DNA if cells are exposed to ionising radiaiotn the samge to DNA can cause mutation sand he cell smay start ividing without conol and this is cancer. very high doses of radiation can kill cells completelt and this is what happens in radiaiton sickness the longer the xposrue to radiato, the more damage caused

what canhappen after ionisation

the changed atoms can initiate other chemical reactions

wha is the amplitude of a wave

the displacement from rest position to the crest

what o the properties of EM waves depnd on expain

the frequency as te freq of EM radation changes its interaction with matter changes th e way a wave is absorbed, reflected, transmitted by a substance depnds on its frequency the EM waves at each end of the spectrum pass through material easiery but those nears the midle are absorbed the higher the fre of EM radiaiton, the more ionising and os the moe harmful and the effects of EM radiaiton on humas depend on the freq of the EM waves

the grater the changein spped of a wave when it mets a medium bundary

the greater the amount of efraction

what is the wavelength f a wave

the length of a full cycle of a ave from crest to crest

what happens when light travelling in the sam edirection refects from an uneven surface e.f. piece of paper crumpled vs evem

the ligt reflects off at different angles if hits even smooth, shiny mirro then light is all reflected at the sae angle and you get a clear reflection

what is the frequency of sound waves

the number of complete vibrations each second e.g. 100HZ vibraes 100 times each second

what is the frequnc of a wave equal to

the reciprocal of its period

what hapens if wves travel along the normal when they hit a medium boundary

the sngle of incidence is 0 so they will change speed but are not refracted and do not change direction

deinf period of wave

the time taken for one whole ccle of a wave

what happen when waves arrive at an obstacle or new material

their direction of travel canbe changedby reflection or refraction

what do EM waves have in common

they all travel at the same speed (speed of light 3x10^8m/s) in a vacuum they are all transverse waves EM waves with higher frequencies have shorter wavelengths

we only see objects because...

they are illuminated and either give out or reflect light and the light enters eyes

waves only hange direction igf...

they meet a new medium at an angle

how do fluorescent lights WORK AND are they safe

they use UV radiaiton to emit visible light and they are safe because all th UV radiaiton is absored by a phosphor coating on the inside of the glass

what do microwaves need to do to work in communiations

to be able to pass through he earth atmosphere

wht is a use of UV light in shops

to dtect forged bank notes banks print special markings in fluorescent ink on their bank notes to detect forgeries under a UV light genuine notes will display the markings but fake notes are often printed on cheaper paper that is slightly fluorescent so they will glow all over but there arenot markings

what type of wave are most aves

transverse

how to protet from sun

use suncream

how are micro waves used in communication

used for satellites and mobil phones - communication two and from satellite sincluding satellite TV use microwaves butt heye mus be microwaves that can pass easily through the earth's watery atmosphere - for satellite TV the signal rom a transmitter is transmitted into space and it picke up by rh satellie receiver dish orbiting thousands of k above the earth the satellite transmits the signal back to earth in a diffeet direction where it is received by a satellite dish on the ground - there is a slight time delay between the signal being sent and received e.g. from UK to australia because of the long istance - mobile phone signals travel from phone to nearesttransmitter as microwaves

what is the main use of radiowaves why are they good at this

used in communication -long wave radio with wavelength of 1-10km can be transmitted around the world because long wavelengths diffract around the earths sured surface and around hills into tunnels so radio signals can be received even if the receiver is not in the line of sight of the transmitter

how do optical fibres work what are they used for

used in phone lines and can carry data over long distances use infrared waes and visibe light - the signal is carried as apulse of light or infrared raditioant and is reflected off the sdes f a very narro core rom one end of the fibre to the other