Chapter 13 Flashcards
why do different types of each wave have different effects?
the energy they transfer depends on the wavelength of the waves
what are the 7 waves?
Radio waves Microwaves Infrared Visible light Ultraviolet X-rays Gamma rays
wavelength of radio waves
between 1m and 1 x 10^4 metres
what type of waves are electromagnetic waves?
transverse
what do EM waves do?
transfer energy from a source to an absorber
wavelength of microwaves
10^-2 metres
wavelength of infrared
10^-5 metres
wavelength of visible light
10^-7 metres
wavelength of ultraviolet
10^-8 metres
wavelength of x rays
10^-10 metres
wavelength of gamma rays
10^-15 metres
what happens to the wavelength as you go down the spectrum (from radio waves to gamma rays)
decreases
what happens to the frequency as you go down the spectrum (from radio waves to gamma rays)?
increases
why is there such a range of wavelengths in the EM spectrum?
the waves are generated by a variety of changes in atoms and atomic nuclei
how fast do all EM waves travel in a vacuum or in space?
3x10^8 metres/second
equation for wavespeed
wavespeed (m/s) = frequency (Hz) x wavelength (m)
what is white light?
light that comes from the sun and ordinary lamps
which colour has the longest wavelength?
red
which colour has the shortest wavelength?
violet
what do all objects emit?
infrared radiation
what happens to the amount of infrared radiation emitted as the object gets hotter?
it increases
why is infrared radiation so damaging?
it heats up cells to can damage or kill them
why is infrared used in optical fibres?
it is absorbed by the glass fibres less than visible light
why are microwaves used in satellite TV and communications?
they can pass through Earth’s atmosphere easily to reach satellites and carry mobile phone signals
why are microwaves used in ovens?
they penetrate food and are absorbed by the water molecules, transferring their energy and heating it
how are microwaves used in satellites?
they are sent out into space by a transmitter
the satellite picks up the signal and transmits it back to earth in a different direction
where it is received by a satellite dish on the ground
why and how is infrared used in TV remote controls?
they are easily produced and received
the controller sends out a series of infrared pulses
how do infrared cameras work?
they detect infrared radiation and convert it to an electrical signal, which is displayed on a screen
how do infrared heaters work?
a wire emits infrared radiation
it is absorbed by the objects in the room
energy is transferred by the infrared waves to their thermal energy stores and they heat up
uses of microwaves 2
communications (satellites)
heating food
properties of microwaves 3
absorbed by water molecules
can travel long distances
usually not harmful
uses of infrared 3
remote controls
heating
thermal imaging
properties of infrared 2
easy and cheap to produce with not much power
can be felt but not seen
uses of radio waves 3
mobile phones
radios
TVs
properties of radio waves
can travel long distances
low energy
normally not harmful
why can micro and radio waves be dangerous?
they can penetrate and heat the body
what are the four carrier waves?
radio waves
infrared
visible light
microwaves
what are carrier waves?
used to carry a signal
properties of shorter wavelength radio waves? 2
carry more information
smaller range
what are fibre optics and how do they work?
they are small glass fibres that transmit signals carried by visible light or infrared radiation
the light rays are reflected and can’t escape the fibre
benefits of fibre optic over radio/microwaves? 2
carry more information (shorter wavelength) more secure (signal can't leave fibre)
why are microwaves commonly used with satellites? 2
they can travel between the satellite and the ground
they don’t spread out so don’t weaken as much as radio waves do
why are radiowaves with short wavelengths used for TV broadcasting from masts?
they carry more information s
why can long wave radio wavelengths be transmitted and received around the world?
the long wavelengths diffract around the curved surface of the earth
why can short wave radio wavelengths be transmitted and received around the world?
they are reflected from the ionsphere so zigzag around the world to their destination
what is the ionsphere?
an electrically charged layer in the earth’s upper atmosphere
how does Bluetooth work?
it uses short wave radio wavelengths to send data over short distances
what are electromagnetic waves made from?
oscillating electric and magnetic fields
what are alternating currents made from
oscillating charges
what is produced when alternating currents oscillate?
electric and magnetic fields (EM waves)
why do microwaves heat food faster than normal ovens?
the waves penetrate into the food and are directly absorbed by it
why don’t ovens absorb microwaves?
they don’t contain water molecules
uses of infrared radiation 3
remote control
night vision
heating
properties of infrared?
easy and cheap to produce, can be felt but not seen
uses of visible light 3
seeing
lighting
signalling
properties of visible light 2
different colours
can reflect and refract
uses of ultraviolet 2
sun beds
security marking
properties of ultraviolet 3
3 types: UVA/B/C
can be harmful in large doses
can be seen by insects
uses of x rays 2
seeing inside body
luggage scanners
properties of x rays 3
can penetrate thin materials
blocked by dense materials like bones
harmful
uses of gamma rays 2
treat cancer cells
kill bacteria
properties of gamma rays 2
highly penetrative
very dangerous - can kill cells
what is fluorescence?
when certain chemicals absorb ultraviolet rays and emit visible light
why are ultraviolet waves harmful to human eyes?
they carry more energy than visible light
differences between x rays and gamma rays
x rays are produced when electrons moving at high speeds are stopped
gamma rays are produced by unstable nuclei releasing electrons
what is ionisation?
when x rays or gamma rays knock electrons out of an atom, making it charged
why is ionising radiation so dangerous?
it can ionise and damage healthy body cells
why are x and gamma rays used in radiotherapy?
they can kill living cells
why are gamma rays used as tracers?
the gamma rays pass out of the body and can be detected so the source is tracked
what is the wavelength of an x ray the same as?
the diameter of an atom
what is radiation dose?
a measure of the damage done to a person’s body by ionising radiation
what does the radiation dose depend on? 3
the type of radiation used
how long the person is exposed to it
the energy the person absorbs from the radiation
what is radiation dose measured in?
sieverts (Sv)
how are x rays produced?
when fast moving electrons hit a target in an x ray tube
what can high doses of radiation cause?
killing live cells
what can low doses of radiation cause?
gene mutation and cancerous growths
2 natural sources of ionising radiation
cosmic radiation from space
radon gas from underground
how many millisieverts are in a sievert?
1000
how are xrays used to destroy tumours?
thick plates between x ray tube and body stops rays from damaging healthy cells
gaps in the plates allow rays to reach and destroy tumour
what is the wavelength of an xray used for imaging like compared to one used for destroying cancerous tumours?
x rays used for imaging have wavelengths that are much longer
why are longer wavelength xrays used for imaging
they don’t carry as much energy
process of x ray imaging
x rays are directed at the body
they pass through soft tissues but are absorbed by denser materials
bones appear white because this is where less x rays pass through
a CCD converts x rays to light and produces an image
what is a CCD and what does it do?
a Charge Coupled Device
sensors in the CCD convert x rays to light
light rays create electronic signals which are sent to a computer to create a visible image
use of lead plates in x rays and why
placed between the tube and the patient to stop rays reaching other body parts
lead is a good absorber of x rays
process of viewing internal organs
patient is given a barium meal
barium absorbs x rays like bones
this shows where blockages are on a radiograph
what is a contrast medium?
a material that absorbs x rays easily
what does the frequency of a wave determine?
the higher the frequency, the more energy transferred
consequences of too much UV radiation? 4
sunburn
premature skin ageing
blindness
increased risk of skin cancer
what is radiation dose?
a measure of the risk of harm from the body being exposed to radiation
what happens when an object that is hotter than its surroundings cools down?
it emits more infrared radiation than it absorbs
what do objects that are at a constant temperature do?
emit IR radiation at the same rate they are absorbing it
what is a perfect black body?
something that absorbs all radiation that hits it
why does the temperature of the earth increase in the day?
more infrared radiation is absorbed and less is emitted
why does the temperature of the earth decrease at night?
less radiation is being absorbed than emitted
what happens to the wavelengths emitted when the temperature of an object increases?
the intensity increases so the peak wavelength decreases
what are the oscillations like on a transverse wave?
they oscillate perpendicularly to the direction of energy transfer
examples of transverse waves 2
electromagnetic waves
ripples/waves on water
examples of longitudinal waves 2
sound waves in air shock waves (eg seismic waves
what are the oscillations like on a longitudinal wave?
parallel to the direction of energy transfer
how does a microphone work?
alternating currents produce oscillating EM waves
the frequency of the waves and current are equal
EM waves travel to transmitter
audio signal supplied to transmitter modulates carrier waves
alternating current causes transmitter aerial to emit radio waves carrying the audio signal
waves received by receiver aerial
oscillations cause receiver to oscillate at same frequency
receiver separates audio signal from carrier waves
audio signal supplied to speaker
sound waves similar to those in radio station are emitted
