Waves - Electromagnetic Waves Flashcards
what is the electromagnetic spectrum
a continuous spectrum of all the possible wavelengths of electromagnetic waves
are electromagnetic waves transverse or longitudinal
transverse
can electromagnetic waves travel through vacuums
yes
do electromagnetic waves with longer wavelengths have higher or lower frequencies
lower
list the basic types of electromagnetic waves in order of increasing wavelength
gamma, x ray, ultraviolet, visible, infrared, microwave, radio
what speed do EM waves travel at
3 x 10^8
how is a EM wave produced due to electron changes
atom absorbs energy and some electrons move to higher energy level. when electron falls back to original level an EM wave is produced
will the EM wave be a high or low frequency if the atomic change that causes the wave has a lot of energy
high
what allows a wide range of frequencies of EM waves to be absorbed by electrons
the huge number of possible changes whiten an atom
how does a nuclear change produce gamma rays
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
what 3 things may a wave do when it reaches a boundary
reflected, absorbed or transmitted
how are radio waves produced
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
how are radio waves received
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.
what is long wave radio used for
(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
what is short length radio wave used for
(10 - 100m) reflected between earth and ionosphere( electrically charged layer in earths upper atmosphere. e.g. Bluetooth
what is medium wave radio used for
can reflect from ionosphere but depends on conditions and time of day
what type of em wave do tv and radio signals use
short wavelength so must be in direct sight of transmitter
why is microwave used for satellite transition
certain wavelength of microwave can pass easily through atmosphere without being reflected, diffracted or absorbed.
what are some applications of satellite communications
satellite tv, phones, internet and military communications
how do satellites work
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
how are microwaves used in cooking
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
all objects emit infrared radiation. why do some objects emit more than others
hotter the object, the more IR
what are infrared radiation cameras used for
detect Ir radiation and monitor temperature. it detects IR radiation and turns it into an electrical signal which is then displayed as a picture
how is infrared radiation used in cooking
temp of food increases when it absorbs IR radiation
how is infrared radiation used in electric heaters
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
what are fibre optic cables
thin glass or plastic fibres that carry data over long distances
how do optical fibres work
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.
where does ultraviolet radiation come from
sun
how do sun tanning lamps work
exposure to UV radiation
how is UV radiation used in security ink
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
how do uv lights work
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.
how are x rays used in medicine
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.
why are x rays good for taking x rays of ppl
x rays pass easily through flesh but not denser material
why are gamma rays good to use as a medical tracker
a gamma emitting isotope can be traced as it travels because gamma rays can easily be passed through the body
what type of rays are used in radiotherapy
x rays and gamma rays
what type of waves cause the most damage
high frequency waves like UV and x ray and gamma rays because they transfer a lot of energy
what damage does UV radiation cause
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
what damage do x ray and gamma ray cause
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
what is the radiation dose
a measure of the risk of harm from the body being exposed to radiation. measured in Sieverts
what 3 things does radiation dosage take account for
total amount of radiation absorbed
how harmful the radiation is
the type of body tissue absorbing the radiation
what do the colour in the colour spectrum correspond to in terms of waves
wavelength
when all the colours in the visible light spectrum are put together what is the name of the light
white light
what are opaque objects
do not transmit light - they absorb some wavelengths of light and reflect others
what does the colour of an object depend on
which wavelength of light they reflect most strongly
what are 2 options to why a banana may be yellow
reflecting yellow light
reflecting red and green light
why is an object white
reflect all wavelengths of visible light equally
why is an object black
absorb all wavelength of visible light
what’s a transparent object
transmit light in straight lines e.g still water or clear glass
whats a translucent object
transmit light but also scatter it so you cant see clearly through them
do translucent and transparent objects absorb and reflect light
may absorb or reflect some
what are colour filters
only transmits certain wavelengths ( colours) and absorbs all other wavelengths. This has the effect of only letting some colours through
if u looked at a red hat through a blue colour filter what colour would it be
black because the blue filter would absorb all colours apart from blue so it would absorb the red pf the hat
what colours would a purple filter let through
let through the wavelengths of the colours that make up purple so blue and red and everything in-between.
if an object which is cooler than its surroundings absorbs more IR radiation than it emits what will happen
warm up
is an object that emits more radiation than than it absorbs hotter or colder than its surroundings
cooling down
how does the surface effect how good it is at emitting and absorbing radiation
black is better than white
matt is better than shiny
what reflects solar radiation back into space
snow
clouds
atmosphere
bright surfaces
radiation is absorbed by the earths surface and the atmosphere. what do they do with the radiation
emit radiation as infrared radiation
what does the overall temperature of the earth depend on
rates at which radiation is absorbed reflected or emitted
