electromagnetic waves (required practical) Flashcards
what type of wave are all electromagnetic waves?
transverse waves.
what are the waves on the electromagnetic spectrum in order?
radio waves. 1m - 10^4m
micro waves. 10^-2m
infrared. 10^-5m
visible light. 10^-7m
ultra violet. 10^-8m
x-rays. 10^-10m
gamma rays. 10^-15m
what is refraction?
waves changing direction at a boundary. between 2 materials
what effects how much a wave refracts?
how much the waves speeds up or slows down. depending on density where higher density gives slow speed
what happens if a wave slows down during refraction?
it bends towards the normal.* if it speeds up it bends away*
what is optical density?
a measure of how quickly light can travel through a material. high optical density means slow speed
what are electromagnetic waves made of?
oscillating electric and magnetic fields.
how are radio waves created?
an alternating current creates oscillations in electrons in a transmitter the frequency of waves is equal to the frequency of ac which emit radio waves that get picked up by a receiver which generates an alternating current of the same frequency.
why are radio waves used for communication?
long wavelengths like radio waves diffract bend around the curved earth surface around hills and into tunnels.
how are short radio waves transmitted over long distances?
short radio waves reflect of ionosphere. an electrically charged layer in the atmosphere
how are long radio waves transmitted over long distances?
long radio waves diffract bend around earths curved surface.
why are micro waves used for communication?
micro waves pass easily through the earth’s watery atmosphere. to talk to satellites
how are micro waves transmitted over long distances?
microwaves are sent into space to get picked up by a satellite which transmits the signal in a different direction and gets received by a radio dish. such as for tv
why are micro waves used in microwaves?
microwaves penetrate a few centimetres into food and heat water molecules cooking the food.
why is infrared radiation used to monitor the temperature?
infrared is emitted by all hot objects which can be detected by infrared camera. higher temperature emits more infrared
how is infrared used to heat things up?
infrared radiation can be released by heating up an object such as wires in a toaster which is absorbed by other objects. such as the toast
how do fibre optic cables transmit data?
pulses of visible light rays are reflected back and forth along a glass or plastic fibre tube until they reach the end of the fibre.
what is ultra violet radiation used for?
fluorescent lights.
security pens.
sun tan. the sun emits UV
artificial sun tan.
why are x rays used for x rays?
x rays pass easily through flesh but not as easily through bones or metal which forms an image based on how much radiation is or isn’t absorbed.
what are some uses of x rays and gamma rays?
x rays.
radiotherapy.
medical tracers.
what makes an electromagnetic wave dangerous?
if it transfers a lot of energy. high frequency waves like UV and gamma
how is ultra violet radiation harmful?
it damages surface cells which can cause sunburn and increases risk of skin cancer.
how is x ray and gamma radiation harmful?
both are types of ionising radiation which can cause gene mutation cell destruction and cancer.
what is white light made of?
all the colours of the visible spectrum.
what are the primary colours? of light (3)
red.
green.
blue.
what is the range in wavelengths of the visible spectrum?
400nm to 700nm.
what does opaque mean?
does not transmit light light cannot pass through but can absorb and reflect it.
what causes object to appear coloured?
the colour of an object depends on which wavelengths are best reflected. the other wavelengths are absorbed
how are not primary colours reflected?
combinations of the primary colours are reflected to make a new colour.
what colours do white and black objects reflect?
white reflects all colours.
black reflects no colour.
what does transparent mean?
see through.
what does translucent mean?
partially see through.
what does a colour filter do?
only transmits specific wavelengths of light.
what happens if you look at an object through a colour of colour filter the object does not reflect?
the object appears black.
how does infrared radiation change with heat?
the hotter an object is the more infrared it releases.
how can you investigate infrared radiation? with a leslie cube
- place an empty leslie cube on a heat proof mat.
- boil water in a kettle and fill the cube.
- wait some time for the cube to heat up and hold a thermometer against each of different surfaces. you should find the surfaces are the same temperature
- hold a infrared detector at a set distance from each of the surfaces and record the infrared amount. you should find more infrared radiation from a black surface and a matt surface than a white surface and a shiny surface
- repeat the experiment multiple times to make sure your results are repeatable.
what is a leslie cube?
a hollow watertight metal cube which has 4 different surfaces such as matte black or shiny metal which can be used to investigate infrared emission.
what is a perfect black body?
an object that absorbs all of the radiation that hits it and no radiation is reflected or transmitted. passed through
how does radiation affect the earth’s temperature?
radiation is absorbed by the earth’s surface which increases the temperature. (some bounces off the atmosphere clouds and the surface and radiation is also emitted by the earth)
