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
