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PHYSICS > SP5: light & the EM waves > Flashcards

SP5: light & the EM waves Flashcards

1
Q

specular reflection

A

reflection of light off a smooth surface

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2
Q

what is the image in a mirror?

A

upright & virtual

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3
Q

diffuse reflection

A

reflection of light from a rough surface, the light is scattered in all directions

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4
Q

refraction core practical steps

A

1) set up a ray box, so that a narrow ray of light is produced

2) place a glass block in the middle of the paper and trace around it

3) use the ray box to shine a ray of light at the block

4) draw crosses up the when the ray hits and leaves the glass block

5) join up the crosses & draw normal lines at each ray

6) remove the block, draw a line joining the ray of incidence & ray of refraction to show the paths of the light rays

7) measure the angle of incidence and angle of refraction for each block

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5
Q

total internal reflection (TIR)

A

the complete reflection of a light ray back into its original medium

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6
Q

what is the critical angle?

A

the minimum angle at which total internal reflection takes place

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7
Q

what condition relating to the incident angle of the wave, must be met for TIR to occur?

A

incident angle > critical angle

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8
Q

TIR and glass fibres

A

-TIR allows light to be contained and guided along very thin fires, usually made of glass (optical fibres)

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9
Q

fibre broadband internet

A

sends computer information coded as pulses of light along underground optical fibres

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10
Q

endoscope

A

-doctors can look at the inside of their patients using an endoscope
-an endoscope is a long tube which guides light into the patient and then guides the reflected light back out to give an image

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11
Q

decorations

A

decorations carry coloured light to different parts of the decoration and let it shine out in different directions

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12
Q

optical fibre construction

A

-different types of glass have slightly different densities
-this causes slight variations in the speed when light travels through the different types of glass
-by making an optical fire’s structure from different types of glass, the light can be made to refract slightly as it travels along the fibre
-this can control the timing of light pulses in the fibre and improves the quality of signal transmissions

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13
Q

spectrum of colour

A

a continuous range of colours, in order of increasing frequency and decreasing wavelength

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14
Q

how are colours seen?

A

the object absorbs all wavelengths except for the colour it is seen as, that colour is then reflected into your eyes

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15
Q

why are some materials transparent?

A

light is transmitted with very little absorption

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16
Q

why are some materials translucent?

A

transmit some light but are not completely clear

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17
Q

why are some materials opaque?

A

they absorb or reflect all light

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18
Q

what is the colour of a translucent obiect determined by?

A

whichever wavelengths are transmitted most

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19
Q

colour filters

A

when white light passes through a coloured filter, all colours are absorbed except for the colour of the filter, orange light is transmitted

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20
Q

why are objects white?

A

they reflect all light

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21
Q

why are objects black?

A

they absorb all the light

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22
Q

primary colour filters

A

only allows one of the three primary colours to be transmitted

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23
Q

non primary colour filters

A

-transmits wavelengths of the same colour as the frequency
-transmits wavelengths of the primary colours that can be added together to make that colour

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24
Q

light primary colours

A

red, blue, green

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25
Q

combinations of primary colours

A

red & green = yellow
green & blue = cyan
blue & red = magenta
red & blue & green = white

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26
Q

what is a lens?

A

-a shaped piece of transparent glass or plastic that refracts light
-when light is refracted it changes direction due to the change in density as it moves from air into glass or plastic

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27
Q

what are lenses used in?

A

eyeglasses, microscopes, telescopes, cameras etc

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28
Q

convex lens

A

-a lens that is thicker in the middle than at the edges and bends light rays towards one another (converging)
-the light rays come together at the focal point
-real or virtual images

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29
Q

concave lens

A

-lens that is thinner in the center than at the edges and separates light rays (diverging)
-light rays appear to come from a focal point on the other side of the lens
-virtual lenses

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30
Q

what is focal length?

A

the distance between the centre of the lens and the focal point

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31
Q

the shorter the focal length…

A

the more powerful the lens

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32
Q

how can you make a lens more powerful?

A

-make it more curved
-change the material

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33
Q

where are images formed?

A

where light rays come together

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34
Q

what is a real image?

A

-always inverted
-usually smaller than object but can be larger

35
Q

when is a real image formed?

A

when the light rays from a point on an object come together to form an image

36
Q

what is a virtual image?

A

-upright
-bigger than the object

37
Q

when is a virtual image formed?

A

formed when light rays don’t come together where the image appears to be

38
Q

what is a ray diagram?

A

shows how light travels

39
Q

how to draw a ray diagram

A
  1. draw a ray from the object to the lens that is parallel to the principal axis, once through the lens, the ray should pass through the principal focus
  2. draw a ray which passes from the object through the centre of the lens
40
Q

focal length

A

the distance from a lens to its focus

41
Q

cameras & the human eye

A

-converging/convex
-image is inverted
-image is diminished
-image is real

42
Q

projectors

A

-converging/convex lenses
-image is inverted
-image is magnified

43
Q

magnifying glass

A

-converging/convex
-image is magnified
-image is upright
-image is virtual

44
Q

peep hole

A

-diverging/concave
-image is upright
-image is diminished

45
Q

principal axis

A

a horizontal line going through the centre of a lens

46
Q

power of lens (dioptres)

A

1/focal length (m)

47
Q

properties of EM waves

A

-transfer energy as radiation from the source of the waves to an absorber
-can travel through a vacuum
-travel at the same speed through a vacuum or the air

48
Q

how fast are EM waves in a vacuum?

A

300,000,000 m/s

49
Q

pneumonic for EM spectrum

A

rich (radio waves)
men (microwaves)
in (infrared)
vegas (visible light)
use (ultraviolet)
expensive (x-rays)
gadgets (gamma)

50
Q

radio waves -> gamma rays

A

long wavelength, low frequency, low energy -> short wavelength, high frequency, high energy

51
Q

uses of radio waves

A

communication:
-broadcasting television, radio, satellite transmissions

52
Q

why are radio waves ideal for communications?

A

-are transmitted easily through air
-do not cause damage if absorbed by the human body
-can be reflected to change their direction

53
Q

how are radio waves used to broadcast information?

A

-radio waves can be produced by vibrations in electrical circuits
-radio waves are absorbed by a conductor & create an alternating current
-this electrical current has the same frequency as the radio waves
-information is coded into the wave before transmission, which can then be decoded when the wave is received

54
Q

how are microwaves that aren’t absorbed by water molecules used?

A

-microwaves pass easily through the atmosphere
-they can pass between stations on earth and satellites in orbit

55
Q

dangers of microwaves

A

internal heating of body cells

56
Q

how are microwaves that are absorbed by water molecules used?

A

-high frequency microwaves have frequencies which are easily absorbed by water molecules in food
-the thermal energy of the molecules increases when they absorb microwaves, which causes heating

57
Q

how is infrared used for cooking food & electrical heaters?

A

-infrared light has frequencies which are absorbed by some chemical bonds
-the internal energy of the bonds increases when they absorb infrared light, causing heating

58
Q

thermal imaging

A

-all objects emit IR, the hotter the object the more IR it will emit
-infrared cameras can detect this
-this is helpful for seeing animals & people in the dark

59
Q

uses of visible light

A

-to see
-optic fibres
-photography

60
Q

how is visible light used in optic fibres?

A

-coded pulses of light travel through glass fibres from a source to a receiver
-used to transmit data really quickly over long distances

61
Q

uses of UV

A

-energy efficient lamps
-to detect forgeries
-to disinfect water
-sun bed

62
Q

how is UV used in energy efficient lamps?

A

-fluorescent substances are used in energy-efficient lamps
-they absorb UV light produced inside the lamp, and re-emit the energy as visible light

63
Q

how is UV used in security?

A

write codes with security pens that are invisible until UV is shined on them

64
Q

how is UV used to sterilise water?

A

the hazardous properties of UV mean it will kill bacteria and can be used for disinfecting water

65
Q

dangers of UV

A

-causes the skin to tan or burn
-increases risk of skin cancer
-damages eyes

66
Q

ionising radiation can…

A

-remove electrons from atoms and molecules
-cause mutations in DNA

67
Q

how are gamma rays produced?

A

decay of radioactive elements

68
Q

what are X-rays used for?

A

medical imaging, security scanning

69
Q

how are x-rays used for medical imaging?

A

x-rays are absorbed by dense structures like bones, which is why x-ray photos are used to help identify broken bones

70
Q

what are gamma rays used for?

A

-sterilising food and medical instruments
-the treatment and detection of cancer

71
Q

external radiotherapy

A

gamma rays are targeted at the cancer site from lots of different angles, so that the cancer site gets the highest dose possible

72
Q

internal radiotherapy

A

-treatment of cancer by putting a radioactive source inside the body, in or next to the cancer
-beta is usually used as it’s more damaging than gamma but can’t pass far through the body

73
Q

radiotherapy side effects

A

healthy cells can be damaged or killed in the process making the patient feel sick

74
Q

medical tracers

A

-radioactive isotopes with short half-lives are injected into or swallowed by the patient
-the movement of isotopes can be tracked by tracking the radiation they emit
-we can check if organs are working properly as they should absorb the right amount of the substance

-gamma rays are used as they are less harmful than alpha or beta

75
Q

changes in temperature caused by the amount of radiation absorbed and emitted

A

increasing temp = more radiation is being absorbed than emitted

constant temp = equal amounts of
absorption and emission

decreasing temp = more radiation is being emitted that absorbed

76
Q

when visible light and high frequency infrared radiation are absorbed by the earth’s surface the planet’s thermal energy…

A

increases, the surface gets hotter

77
Q

what happens to low frequency infrared that the earth emits?

A

-some is transmitted out into space
-some is absorbed by greenhouse gases in the atmosphere which emit the IR in all directions -> some into space, some back to earth

78
Q

the greenhouse effect

A

naturally occurring greenhouse gases stabilise the surface temperature of earth, allowing it to support life

79
Q

climate change

A

-humans adding to the natural greenhouse effect, causing infrared radiation to be
‘trapped’ and reabsorbed by the earth’s surface
-this is causing global temperatures to increase

80
Q

equipment in infrared core practical

A
  • leslie cube (has 4 different types of surface and is filled with hot water to increase its temperature)
    -infrared detector
    -heatproof mat
81
Q

method of infrared practical

A
  1. place a leslie cube on a heat-resistant mat. almost fill it with boiling water and replace the lid
  2. leave for one minute. this is to enable the surfaces to heat up to the temperature of the water.
  3. use the infrared detector to measure the intensity of infrared radiation emitted from each surface, or the temperature of the surface. make sure that the detector is the same distance from each surface for each reading
82
Q

which side of the leslie cube is the hottest?

A

matte black

83
Q

which side of the leslie cube is the coolest?

A

shiny silver

PHYSICS (15 decks)

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