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physics > waves: electromagnetic waves > Flashcards

waves: electromagnetic waves Flashcards

1
Q

what are electromagnetic waves?

A

electromagentic waves are transverse waves that transfere energy from the source of the waves to an absorber.

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2
Q

what type of spectrum do electromagnetic waves form?

A

a continuous spectrum

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3
Q

order the types opf electromagnetic radiation from long wavelength to short wave length

A
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4
Q

how does the speed of electromagnetic radiation differe in a vacumm and air?

A

electromagnetic radition travels at the same speed

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5
Q

what is the order of the different light colours from low frequency to higher frequency?

A

ROYBGIV

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6
Q

what are examples of electromagnetic waves trasfering from an source to an absorber?

A
  • micorwave transfere energy from the source (the oven) to the absorber (the food)
  • light waves transfere energy from the source (sun) to the absorber (solar panels)
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7
Q

whcih electromagnetic wave can our eyes detect?

A

only visible light

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8
Q

what property of waves in different mediums causes refraction??

A
  • difference of the velocity of the waves in different substances
  • wave speed is slower in denser materials, causing refraction
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9
Q

when does refraction happen?

A

when a wave chnages speed as it passes from one medium to another

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10
Q

in which direction ( relative to the normal) do waves refract when entering a denser medium?

A
  • they bend tworads the normal
  • the angle of refraction is less than the angle of incidence
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11
Q

what is the normal?

A

This line is perpendicular to the surface of the boundaries

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12
Q

describe in which direction relative to the normal do the waves refract when entering a less dense to dense, dense to less dense, and along the normal.

A
  • From less dense to more dense (e.g air to glass), light bends towards the normal
  • From more dense to less dense (e.g. glass to air), light bends away from the normal
  • When passing along the normal (perpendicular) the light does not bend at all
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13
Q

describe this picture and why the waves refract?

A
  • The change in direction occurs due to the change in speed when travelling in different substances
  • When light passes into a denser substance the rays will
    slow down, hence they bend towards the normal
  • when the light passes from the glass and leaves the velocity increases
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14
Q

what properties of the wave change and stay the same? why?

A

speed and wavelgth chnage but the frequency does not
* this is because different frequncies account for different colours and when a light refracts it does not change colour

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15
Q

what happenes when EM waves move from one medium to another?

A

the waves might be:
* transmitted
* reflected
* absorbed
* refracted

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16
Q

why do materials intercat with each wave differently?

A

The material interacts differently with different parts of EM spectrum because of the difference in wavelength

17
Q

which of the interactions happen depends on what?

A
  • The wavelength of the waves
  • The material the wave is travelling through
18
Q

just pictures of refraction of light in different shapes

A
19
Q

what is a wavefront diagram?

A

an imaginary line which connects all the same points in a set of waves

20
Q

explain refraction using the wavefront diagram

A
  • When a wave hits a different medium the different parts of the wave enter the medium at different times leads to a change in speed
  • The difference in speed between the parts of the wave in the first medium and the parts in the second medium causes the wave to bends which leads to a change in direction ( refraction)
21
Q

what is the pratical to investigate how the amount of infrared radiation is radiated by a surface depends on the nature of that surface?

A
22
Q

how to investigate the absorption of infrared by different surfaces

A
  • have 2 metal plates
  • one plate is shiny metalic the other is matt black
  • on the back attach a drawing pin with vasiline
  • switch on the heater and stopwatch
  • tempertaure of metals plate increase as they absorb infrared
  • record time it takes for vasline to melt and pin to fall
  • pin falls of matt black surface first as it absorb and emmiting than shiny metalic
23
Q

how can radiowaves be produced?

A

by oscillations ( move backwords and forwards) in electrical circuits

24
Q

what happesn when radio waves are absorbed?

A

when radiowaves are absorbed they may create an alternating current with the same frequency as the radiowave itself so radio waves can themselves induce oscillations in an electrical
circuit.

25
Q

in which 2 ways can atoms recat with electromagnetic waves?

A
  • absorbed
  • emitted
26
Q

what happens when electrogmagnetic waves are absorbed?

A

this causes changes to atoms as an example:
When an EM wave hits an atom, it can be absorbed by one of the electrons giving it energy
This causes the electron to move up to a higher energy level

If an electron moves down to a lower energy level it will emit an EM wave in the process

In this way, atoms can absorb and emit electromagnetic waves over a wide range of frequencies

27
Q

where do gamma rays originate from?

A

Gamma rays originate from changes in the
nucleus of an atom.

28
Q

Changes in atoms and the nuclei of atoms can result in what?

A

electromagnetic waves being generated or absorbed over a wide
frequency range

29
Q

what EM waves have hazaerdous effects on human body tissue?

A

Ultraviolet waves, X-rays and gamma rays

30
Q

how is ultra-violet hazardous to the human body tissue?

A

increase skin cancer + causses skin to age prematurly

31
Q

how is xrays and gamma rays hazardous to the human body tissue?

A
  • they are ionising radiation (knock electrons off when they are absorbed)
  • because of this they can cuase mutations in the gene and increase risk of cancer.
32
Q

the damadges caused by the radition depends on what?

A

on the type of
radiation and the size of the dose

33
Q

what is the defenition of radiation dose?

A

Radiation dose (in sieverts) is a
measure of the risk of harm resulting from an exposure of the body
to the radiation
* 1000 millisieverts (mSv) = 1 sievert (Sv)

34
Q

what are the uses of the radiowaves?

all of them

A
  • radio waves – television and radio
  • because they can travel long diantces before being absorbed by building or trees
  • refelct off a layer of charged particles in the atmosphere so it can be sent veery long distances around the earth
35
Q

what are the uses of microwaves?

A
  • microwaves – satellite communications, cooking food
  • this is because most food contain water molelecules which absorb the energy of microwaves, energy causes temp of food to increase
  • pass through eath atmosphere without being relfectled or refracted ( good for sattelite)
36
Q

what are the uses of infrared?

A
  • infrared – electrical heaters, cooking food, infrared cameras
  • this is because the energy of infrared is easily absorbed by surface of objects
37
Q

what are the uses for visible light?

A
  • visible light – communication using fibre optics
  • this is because visible light has a short wavelength so can carry a great deal of information
38
Q

what is the use of ultraviolet?

A
  • ultraviolet – energy efficient lamps, sun tanning
  • this is because ultraviolet has a short wavelgth it can carry more energy than visible light ( loight bulbs)
39
Q

what is the use of xrays and gamma rays?

A
  • X-rays and gamma rays – medical imaging and treatments.
  • this is because they are very penetrative ( can pass easily through body tissue)
    *

physics (11 decks)

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