Waves 2

when is light refracted

when it reaches the interface (boundary) between two different media (things light travels through)

what happens when light is refracted

it changes direction and speed

what happens when light goes from a less dense to more dense material

it slows down and bends towards the normal so angle gets smaller

what happens when light goes from a more dense to a less dense material

speeds up and bends away from the normal so angle gets bigger

what does normal mean

right angle

what does it look like when light is refracted to more dense then to less dense

see image

what are ray diagram rules

draw ray of light as a straight line with arrow in the middle with rays in the air parallel to each other

draw normal as a dashed line at a right angle to the surface where light hits the boundary

label incident ray and refracted ray and angle of incidence and angle of refraction

what happens when wave fronts enter parallel to the boundary going from deep to shallow water

every point on the wave front enters the shallow water at the same time so every point on the wave front slows down at the same time therefore the direction stays the same but the wave front behind it is still travelling at a higher speed so starts to catch up before entering the shallow water and so wavelength decreases

what happens when wave fronts enter at an angle to the boundary

the speed of the waves is slower in the shallow water so the edge of the wave front entering the shallow water slows down and the part of the wave front in the deeper water continues at a higher speed getting ahead leading to a change in direction

what does light dispersion look like

looks like pink floyd dark side of the moon

what are the wavelengths of radio waves

long with a low frequency in m / km

what are the key uses of radio waves

to broadcast radio and television

how do radio wave transmissions work

electrons in the transmitter oscillate back and forth which produces a radio wave which is transmitted through the air. at the receiving ariel the metal ariel absorbs the radio waves creating an alternating current with the same frequency as the transmitted wave

how can we send waves to different countries e.g. england to america if the earth is round

reflection of radio waves by the ionosphere allows waves to travel from england to america

what is the speed of radio waves microwaves and UV waves in a vacuum

3×10 to the 8 m/s

what are the wavelengths of microwaves

relatively long with relatively low frequency in cm

what are key uses of microwaves

cooking satellite communications mobile phones

what are the dangers of microwaves

some heating effect so could damage cells

how do microwaves travel

in narrow beams without spreading out and are transmitted through the atmosphere into space

what is an optical fibre

a glass wire that visible light and infrared radiation can travel along

why is infrared used in preference to light for communication

it is absorbed less than light

what are the typical wavelengths of ultraviolet

relatively short with high frequency around 100nm

what are the key uses if ultraviolet

sun tanning and energy efficient lamps

what are dangers of ultraviolet

sunburn premature ageing of skin and ionising radiation which can cause mutations in DNA in cells and cancer

how do we view invisible or security ink with UV light

the UV light is absorbed by the invisible ink which causes it to emit light in the visible spectrum so we can read it

how does UV work in fluorescent lamps

the UV light is absorbed by the coating around the fluorescent lamps causing it to emit light in the visible spectrum

why are visible light wavelengths better than UV light wavelengths

UV waves carry more energy than visible light waves so are more harmful to the human eye by damaging cells in the eye leading to blindness

what happens when x rays and gamma rays reach a boundary

they both travel straight into substances and pass through as long as the substance is not too thick for example a thick lead plate will stop them

similarities of x rays and gamma rays

they both are at the short wavelength end of the electromagnetic spectrum and carry more energy per second than longer wavelength electromagnetic waves

differences between x rays and gamma rays

x rays are produced when electrons or other particles moving at high speeds are stopped whereas gamma rays are produced by radioactive substances. gamma rays have a shorter wavelength than x rays so can penetrate substances more

what is the order of the electromagnetic spectrum from long wavelength (low frequency) to short wavelength (high frequency)

radio waves, micro waves, infrared, visible light, UV, x rays, gamma rays

how do x rays work

x ray machine sends x rays towards the body which transmit through the body and most go through onto the photographic plate behind the body making it go dark. however the bones and dense parts of the body absorbs some of the x rays leaving that part of the photographic plate white which overall creates an image

what is the relationship between infrared and temperature

the hotter an object the more infrared it radiates

what is the relationship between infrared and surface area

the larger an objects surface area the more infrared it radiates

what are good absorbers also

good emitters

what is thermal equilibrium (constant temp)

when an object emits and absorbs the same amount of infrared radiation

what are dark matt objects the best at

emitting and absorbing

what are bright shiny objects the worst at

emitting and absorbing

if an object is cooling what is it doing

emitting radiation at a higher rate than it is absorbing radiation

what is a perfect black body

an object which absorbs all radiation so does not transmit or reflect any and is also the best possible emitter

how does the heating and cooling of the earth work during the day and night

the earth is cooler than the sun so emits less energy than the sun so during the day more energy is absorbed by the surface than emitted by it however during the night no energy from the sun reaches the surface so the surface cools

how do clouds affect the temperature of the earth

clouds are good reflectors of radiation so during the day more energy is reflected away than towards the earth so the surface cools whereas during the night no energy is present to be reflected away so energy is only reflected back warming the surface

explain the infrared radiation required practical

get four cubes with four surfaces of matt black matt white shiny black and shiny silver. fill a kettle with hot water and put it in each of the four cubes making sure there is the same amount and temperature of water in each. point an infrared detector at one of the cubes and read the value of it to see how much infrared it emitted and then repeat this with the other cubes keeping the same distance between the surface of the cubes and the infrared detector each time