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Physics > P13 Electromagnetic spectrum > Flashcards

P13 Electromagnetic spectrum Flashcards

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1
Q

What are electromagnetic waves

A

transverse waves that transfer energy from a source to an absorber

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2
Q

what speed do EM waves travel through air or a vacuum

A

the same speed - the speed of light

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3
Q

what spectrum do electromagnetic waves form

A

a continuous spectrum over a range of frequencies

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4
Q

how can EM waves be grouped and ranked

A

in terms of frequency and wavelength into seven basic types

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5
Q

why is there such a wide range of frequencies for EM waves

A

because they are generated by a variety of hcnages in atoms and thier nuclei

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6
Q

what are EM waves caused by

A

something with an electrical charge osillating

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7
Q

what are the seven EM wave types

A
  • radio waves
  • microwaves
  • infrared waves
  • visiable light
  • ultraviolet
  • x-rays
  • gamma rays
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8
Q

which EM wave has the smallest wavelength

A

gamma rays

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9
Q

which EM wave has the biggest frequency

A

gamma rays

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10
Q

which EM wave has the biggest wavelength

A

radio waves

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11
Q

which EM wave has the smallest frequency

A

radio waves

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12
Q

what are EM waves made up of

A

oscillating electric and magnetic fields

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13
Q

how can you produce radio waves using an alternating current in an electrical circuit

A
  • the object with the charges (electrons) oscillate to create the radio waves is a transmitter
  • when the transmitted radio waves reach a receiver they are absorbed
  • the energy carried is transferred to the electrons in the reciever
  • causing the electrons to oscillate ~ generating an alternating current
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14
Q

what are radio waves main use

A

communication

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15
Q

why can long-wave radio waves be recieved even if the receiver isn’t in the line of sight of the transmitter

A

because long wavelengths diffact (bend) around the curved surface of the Earth, hills or into tunnels

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16
Q

can short-wave radio waves be recieved from long distances and why

A

yes because they are reflected from the ionosphere

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17
Q

what is the ionosphere

A

an electrically charged layer in the Earth’s upper atmosphere

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18
Q

what type of radio waves does bluetooth use

A

short-wave radio waves

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19
Q

what are microwaves used for

A

satellite communication and microwave ovens

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20
Q

why are microwaves best for satellite communication

A

because they pass easily through the Earth’s watery atmosphere

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21
Q

how does satellite communication work

A
  • signal from transmitter is transmitted into space
  • picked up by satellite receiver dish
  • satellite transmits the sign back down to earth
  • it is received by a satellite dish on the ground
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22
Q

how do microwaves work in microwave ovens

A
  • the microwaves are absorbed by the water molecules in the food
  • transferring the energy to the water molecules causing the food to heat up
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23
Q

what can infrared radiation be used to do

A

increase or monitor temperatures

24
Q

describe the relationship between hot objects and infrared radiation

A

the hotter the object the more infrared radiation it gives out

25
Q

how do infrared cameras work

A
  • camera detects the IR radiation and turns it into an electrical signal which is displayed on a screen
  • the hotter the object the brighter it appears
26
Q

how do electrical heaters heat a room

A
  • the wire heats up inside the heater
  • the wire emits lots of IR radiation
  • it is absorbed by the objects and the air in the room
  • transferring the energy to the thermal energy stores of the objects
27
Q

what can visible light be used for

A

in fibre optic cables to transmit data

28
Q

what are fibre optic cables

A

thin glass or plastic fibres that can carry data (from phones or TVs) over long distances as pulses of visible light

29
Q

how do fibre optics work

A

the light rays reflect and bounce back and fourth until they reach the end of the fibre

30
Q

what is fluorescence

A

a property of certain chemicals where ultraviolet radiation is absorbed and then visible light is emitted

31
Q

what are the uses of ultraviolet radiation

A
  • tanning
  • fluorescent lights
  • sterelising
32
Q

what is UV produced by

A

the sun

33
Q

what are x-rays and gamma rays used for

A
  • sterilise
  • security in airports
  • imaging in medicine
34
Q

how do x-ray photographs work

A
  • x-rays easily pass through flesh but not rhough denserr metals like bones and metal
  • the amount of radiation absorbed gives you an image
35
Q

what do radiographers use x-rays and gamma rays for

A

to treat people with cancer using radiotherapy

36
Q

how does radiotherapy work

A
  • high doses of x-rays and gamma rays kill all living cells
  • directing them onto cancer cells can killl them
37
Q

how do medical professionals stay safe when using x-rays and gamma rays

A
  • wear lead aprons
  • stand behind a lead screen
  • leave the room
38
Q

why do medics use lead to protect themselves from rays

A

because lead is very dense and a good absorber so it will absorb the x-rays and gamma rays

39
Q

why are ultraviolet, x-rays and gamma rays so dangerous

A

they are ionising - can knock electrons off of atoms

40
Q

what does ionising radiation cause

A
  • gene mutation
  • cell destruction
  • cancer
41
Q

what is taken into account before ionising EM waves are used

A

whether the benefits outweigh the health risks

42
Q

what are radiation doses measured in

A

sieverts (Sv)

43
Q

what is radiation dose

A

a measure of the risk of harm from the body being exposed to radiation

44
Q

what does the risk of radiation dose depend on

A
  • total amount of radiation
  • radiation type
  • time exposed
45
Q

are radiation risks the same amount all over the body

A

no - it is riskier to have radiation emitted on your chest rather than your head

46
Q

how do we perceive visible light

A

as different colours - each colour is it’s own wavelength

47
Q

when all colours are put together what light does this create

A

white light

48
Q

what does the colour and transparency of an objecct depend on

A

the absorbed wavelengths

49
Q

why are some objects opaque

A

because they do not trasmit light - they absorb it and reflect it

50
Q

what is the colour of an opaque object determined by

A

which wavelength of light is most reflected

51
Q

what makes an object white

A

they reflect all of the visible light wavelengths equally

52
Q

what makes an object black

A

they absorb all wavelengths of visible light

53
Q

what makes an object transparent or translucent

A

they transmit light - the light is passed through the object not just reflected or absorbed

54
Q

what are colour filters used for

A

to filter out different wavelengths of light so only certain wavelengths are transmitted

55
Q

what is the health probem caused by using sunbeds too much

A

skin cancer

56
Q

why are some humans short sighted

A

because the eyeball is too long

57
Q
A

Physics (12 decks)

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