topic 3 - waves and the em spectrum Flashcards
7 groups of the EM spectrum
radio micro infrared visible light ultra violet x-rays gamma rays
wavelength range radiowaves
1m - 10^-4m
wavelength range microwaves
10^-2m
wavelength range infrared
10^-5m
wavelength range visible light
10^-7m
wavelength range ultraviolet
10^-8m
wavelength range x-rays
10^-10m
wavelength range gamma rays
10^-15m
what colour has the longest wavelength
red
what colour has the shortest wavelength
violet
how are EM waves made with a.c
alternating currents are made up oscillating charges
as charges oscillate, they produce oscillating electric and magnetic fields (EM waves)
how do radiowaves in a transmitter induce a.c in a receiver (5)
1) a.c supplied to transmitter
2) electrons oscillate to produce EM waves
3) emitted radio waves transfer energy
4) at receiver, EM waves are absorbed, causing electrons in the receiver to oscillate
5) this produces a.c in the receiver
uses of radiowaves (2)
broadcasting
communications and satellite transmissions
how are radiowaves used in broadcasting (3)
long wave radiowaves can be received halway around the world from where they started as they bend around the Earth’s curved surface
short wave radiowaves can be received at long distances from the transmitter as they are reflected by the Earth’s atmosphere (used by bluetooth)
very short wavelengths are used for tv and fm transmissions but in order to get a signal, the receiver has be in direct sight
uses of microwaves (2)
cooking
communications and satellite transmissions
how are microwaves used in cooking
microwaves are absorbed by water molecules in the food
they can penetrate a few cm before being absorbed and transferring the energy they are carrying to the water molecules causing it to heat up
water molecules transfer energy to rest of food molecules by heating
how are radiowaves and microwaves used in communications and satellite transmissions
microwaves or high frequency radiowaves
they pass easily through the Earth’s watery atmosphere to a satellite receiver dish orbiting the eearth
that transmits the signal back to earth in a different direction where it is received by a satellite dish
what is infrared radiation used for (6)
cooking thermal imaging short range communications optical fibres TV remote controls security systems
how is infrared radiation used for cooking
absorbing IR radiation causes objects to get hotter so food can be cooked using IR radiation as the temperature of the food increases
how is infrared radiation used for thermal imaging
infrared cameras can be used to detect infrared radiation and monitor temperature
camera detects IR radiation, converts it to an electrical signal and this is displayed on a screen as a picture
this is used by the police to see suspects trying to escape or hide in the dark
how is infrared radiation used for short range communications
transfer of information across short distances
the receiver has to be in the line of sight of the emitter
can be used to send files between mobile phones or laptops
how is infrared radiation used for optical fibres
thin glass or plastic fibres can carry data over long distances as pulses of IR radiation (usually uses one wavelength to prevent dispersion)
uses total internal reflection to send data over long distances
how is infrared radiation used in tv remote controls
transfer data over a short distance from the remote to the TV
some phones have the software builtin to do this now
how is infrared radiation used in security systems
if a change in infrared radiation is detected, an alarm sounds or a security light turns on
what is visible light used for (3)
vision
photography
illumination
how is visible light used for vision
visible light is the light we see
how is visible light used for illumination
we use the light we see for lighting up things in order to be able to see them
how is visible light used for photography
traditional photography uses photographic film which reacts to form an image
digital photography contains image sensors that detected visible light and generate an electrical signal which is converted to an image that can be stored digitally or printed
what is UV light used for (4)
security marking
fluorescent lamps
disinfecting water
detecting forgery
how is UV light used for security marking
security pens can mark property
under UV light the ink will glow but it is invisible otherwise , helping to identify stolen property
how is UV light used for fluorescent lamps
fluorescent chemicals absorb UV radiation and then emit visible light
fluorescent lights use UV to emit visible light and are energy efficient
how is UV light used for disinfecting water
used to sterilise water sometimes
it kills bacteria in the water making it safe to drink
how is UV light used for detecting forgery
genuine bank notes and passports have special markings that only show up under UV light
what are X-rays used for (3)
internal structure observation
airport security scanners
medical x-rays
how are x-rays used for internal structure observation
x-rays affect photographic film in the same way as light
so you can take x-way photographs to view internal structure
how are x-rays used for airport security scanners
used to detect hidden objects that can’t be detected using metal detectors
how are x-rays used for medical x-rays
radiographers take x-rays to help identify broken bones
x-rays are transmitted by flesh by absorbed by denser materials
radiation is passed through the object or body onto a detector (the brighter parts are where fewer x-rays got though) producing a negative image
what are gamma rays used for (3)
sterilisation of food/medical equipment
cancer detection
cancer treatment
how are gamma rays used for sterilisation of food/medical equipment
works by gamma rays killing microbes
this keeps food fresh to eat for longer
sterilising medical equipment by killing microbes is good
how are gamma rays used for cancer detection
can be detected using tracers which use gamma rays
how are gamma rays used for cancer treatment
we can target cells with gamma radiation but doctors have to be careful not to cause damage to healthy cells nearby
dangers of microwaves
some wavelengths of microwaves can be absorbed causing internal heating of cells which can be dangerous
dangers of IR radiation
can cause burns if skin gets too hot
dangers of UV light (3)
ionising radiation
damage to surface cells that could lead to skin cancer
damager to eyes causes eye conditions or blindness
dangers of x-rays and gamma rays
can potentially cause mutations and damage to cells
potentially leading to cancer
due to higher frequencies, more energy is transferred so more damage
