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Physics > Waves - Electromagnetic Waves > Flashcards

Waves - Electromagnetic Waves Flashcards

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1
Q

what is the electromagnetic spectrum

A

a continuous spectrum of all the possible wavelengths of electromagnetic waves

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2
Q

are electromagnetic waves transverse or longitudinal

A

transverse

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3
Q

can electromagnetic waves travel through vacuums

A

yes

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4
Q

do electromagnetic waves with longer wavelengths have higher or lower frequencies

A

lower

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5
Q

list the basic types of electromagnetic waves in order of increasing wavelength

A

gamma, x ray, ultraviolet, visible, infrared, microwave, radio

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6
Q

what speed do EM waves travel at

A

3 x 10^8

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7
Q

how is a EM wave produced due to electron changes

A

atom absorbs energy and some electrons move to higher energy level. when electron falls back to original level an EM wave is produced

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8
Q

will the EM wave be a high or low frequency if the atomic change that causes the wave has a lot of energy

A

high

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9
Q

what allows a wide range of frequencies of EM waves to be absorbed by electrons

A

the huge number of possible changes whiten an atom

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10
Q

how does a nuclear change produce gamma rays

A

unstable nuclei of radioactive atoms decay, giving out particles. the nucleus then might need to get rid of extra energy by giving out a gamma ray

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11
Q

what 3 things may a wave do when it reaches a boundary

A

reflected, absorbed or transmitted

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12
Q

how are radio waves produced

A

alternating currents are made up of oscillating charges which produce oscillating electric and magnetic fields which are radio waves. the frequency of the radio waves are equal to the frequency of the ac. The object is called the transmitter

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13
Q

how are radio waves received

A

absorbed by receiver. energy carried by waves are transferred to kinetic energy stores of the electrons in the material . this causes electrons to oscillate and generate an ac which has the same frequency as the radio wave which generated it.

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14
Q

what is long wave radio used for

A

(1- 10km) transmitted and received half way across world cus they bend around curved surface of earth. Can diffract around hills and into tunnels. diffraction effect means receiver does not have to be in line of sight

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15
Q

what is short length radio wave used for

A

(10 - 100m) reflected between earth and ionosphere( electrically charged layer in earths upper atmosphere. e.g. Bluetooth

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16
Q

what is medium wave radio used for

A

can reflect from ionosphere but depends on conditions and time of day

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17
Q

what type of em wave do tv and radio signals use

A

short wavelength so must be in direct sight of transmitter

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18
Q

why is microwave used for satellite transition

A

certain wavelength of microwave can pass easily through atmosphere without being reflected, diffracted or absorbed.

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19
Q

what are some applications of satellite communications

A

satellite tv, phones, internet and military communications

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20
Q

how do satellites work

A

signal from transmitter is transmitted into space and picked up by satellite. Satellite transmits signal back to earth in different direction and is received by a satellite receiver on ground. slight time delay cus of long distance

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21
Q

how are microwaves used in cooking

A

wavelengths which allow them to be absorbed by water molecules in food. penetrate food and when absorbed they transfer energy to thermal energy store of water molecules. the water molecules then transfer energy to rest of the food

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22
Q

all objects emit infrared radiation. why do some objects emit more than others

A

hotter the object, the more IR

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23
Q

what are infrared radiation cameras used for

A

detect Ir radiation and monitor temperature. it detects IR radiation and turns it into an electrical signal which is then displayed as a picture

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24
Q

how is infrared radiation used in cooking

A

temp of food increases when it absorbs IR radiation

25
Q

how is infrared radiation used in electric heaters

A

contain long pieces of wire that heat up when current flows through it. The wire then emits lots of IR radiation and the emitted radiation is absorbed by objects in air and room.

energy is transferred by Ir waves to the thermal store of objects

26
Q

what are fibre optic cables

A

thin glass or plastic fibres that carry data over long distances

27
Q

how do optical fibres work

A

pulses of visible light are used. When light hits wall of fibre its reflected back to the fibre so light bounces back and forth until it reaches end of the fibre.

28
Q

where does ultraviolet radiation come from

A

sun

29
Q

how do sun tanning lamps work

A

exposure to UV radiation

30
Q

how is UV radiation used in security ink

A

when UV radiation hits fluorescence its absorbed and visible light is emitted. so police can put UV light on valuable items to identify them if its stolen

31
Q

how do uv lights work

A

glass tubes coated on the inside with a fluorescent material. then filled with mercury and noble gases like neon and argon. when electrical current is switched on, electrons in mercury are excited to higher energy levels. When they fall back, UV is emitted which hits fluorescent coating and converted to visible light. energy efficient.

32
Q

how are x rays used in medicine

A

x ray directed through patient towards detector plate. Plate starts off white, the bits exposed to fewest x rays ( areas where x ray has been absorbed by bone) remain white. Where x ray has passed through soft tissue without being absorbed turn black.

33
Q

why are x rays good for taking x rays of ppl

A

x rays pass easily through flesh but not denser material

34
Q

why are gamma rays good to use as a medical tracker

A

a gamma emitting isotope can be traced as it travels because gamma rays can easily be passed through the body

35
Q

what type of rays are used in radiotherapy

A

x rays and gamma rays

36
Q

what type of waves cause the most damage

A

high frequency waves like UV and x ray and gamma rays because they transfer a lot of energy

37
Q

what damage does UV radiation cause

A

damages surface cells which can lead to sunburn and causes skin to age prematurely. also damage to eyes and an increased risk of skin cancer

38
Q

what damage do x ray and gamma ray cause

A

they are types of ionizing radiation so they can carry enough energy to knock electrons off of atoms. This can kill cells or cause gene mutations which can lead to cancer

39
Q

what is the radiation dose

A

a measure of the risk of harm from the body being exposed to radiation. measured in Sieverts

40
Q

what 3 things does radiation dosage take account for

A

total amount of radiation absorbed

how harmful the radiation is

the type of body tissue absorbing the radiation

41
Q

what do the colour in the colour spectrum correspond to in terms of waves

A

wavelength

42
Q

when all the colours in the visible light spectrum are put together what is the name of the light

A

white light

43
Q

what are opaque objects

A

do not transmit light - they absorb some wavelengths of light and reflect others

44
Q

what does the colour of an object depend on

A

which wavelength of light they reflect most strongly

45
Q

what are 2 options to why a banana may be yellow

A

reflecting yellow light

reflecting red and green light

46
Q

why is an object white

A

reflect all wavelengths of visible light equally

47
Q

why is an object black

A

absorb all wavelength of visible light

48
Q

what’s a transparent object

A

transmit light in straight lines e.g still water or clear glass

49
Q

whats a translucent object

A

transmit light but also scatter it so you cant see clearly through them

50
Q

do translucent and transparent objects absorb and reflect light

A

may absorb or reflect some

51
Q

what are colour filters

A

only transmits certain wavelengths ( colours) and absorbs all other wavelengths. This has the effect of only letting some colours through

52
Q

if u looked at a red hat through a blue colour filter what colour would it be

A

black because the blue filter would absorb all colours apart from blue so it would absorb the red pf the hat

53
Q

what colours would a purple filter let through

A

let through the wavelengths of the colours that make up purple so blue and red and everything in-between.

54
Q

if an object which is cooler than its surroundings absorbs more IR radiation than it emits what will happen

A

warm up

55
Q

is an object that emits more radiation than than it absorbs hotter or colder than its surroundings

A

cooling down

56
Q

how does the surface effect how good it is at emitting and absorbing radiation

A

black is better than white

matt is better than shiny

57
Q

what reflects solar radiation back into space

A

snow
clouds
atmosphere
bright surfaces

58
Q

radiation is absorbed by the earths surface and the atmosphere. what do they do with the radiation

A

emit radiation as infrared radiation

59
Q

what does the overall temperature of the earth depend on

A

rates at which radiation is absorbed reflected or emitted

Physics (13 decks)

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