Topic 6 - Waves Flashcards
(31 cards)
What are transverse waves?
the oscillations are perpendicular to the direction of the energy transfer
what are examples of transverse waves?
- all electromagnetic waves e.g. light
- ripples in water
- a wave on a string
what are longitudinal waves?
the oscillations are parallel to the direction of energy transfer
what are examples of longitudinal waves?
- sound waves e.g. ultrasound
- shock waves
what 3 things can happen to waves?
absorbed, transmitted, reflected
what is the rule for all reflected waves?
angle of incidence = angle of reflection
what are the two type of reflection?
specular reflection - when a wave is reflected in a single direction by a smooth surface e.g. when light is reflected by a mirror you get a clear reflection
diffuse reflection - a wave is reflected by a rough surface (e.g. a piece of paper) and the reflected rays are scattered in lots of different directions
why are light rays scattered in diffuse reflection?
because the normal is different for each incoming ray so the angle of incidence is different for each ray
what are em waves?
- electromagnetic waves are transverse waves that transfer energy from a source to an absorber
- they all travel at the same speed through air or a vacuum
- they form a continuous spectrum split into 7 separate parts based on their frequency and wavelength
what happens to friequency and wavelength along the spectrum?
from left to right frequency increases and wavelength decreases
what is the order of the electromagnetic spectrum?
radio waves, micro waves, infra red, visible light, ultraviolet, x-rays, gamma rays
what are em waves made up of?
oscillating electric and and magnetic fields
how are radio waves produced?
- transmitters can be used to produce radio waves by using an alternating current in an electric circuit , electrons oscillate and produce radio waves
- transmitter is connected to an oscilloscope to see the frequency of the ac, the frequency of the ac determines the frequency of the wave produced
- transmitted radio waves reach a receiver and are absorbed, the energy is transferred to the electrons in the receiver causing them to oscillate and it generates another ac displayed on another oscilloscope
- current has the same frequency as the radio waves that generated it
what are the different types of radio waves?
long waves, short waves, medium waves
what are long radio waves?
- they travel huge distances (wavelengths of 1-10km)
- this is because long wavelengths diffract (bend) around the curved surface of the earth
- they can also diffract around hills, into tunnels
- this makes it possible for radio signals to be received even if the receiver isn’t in the line of sight of the transmitter
what are short radio waves?
- signals can be received at long distances (wavelengths of about 10m-100m)
- this is because they are reflected from the ionosphere (an electrically charged layer in the earths upper atmosphere)
what are medium waves?
- can also reflect from the ionosphere depending on the atmospheric conditions
what are the uses of radio waves?
- bluetooth uses short wave radio waves to send data over short distances between devices without wires
- radio waves used for TV and FM radio have very short wavelengths, they have to travel directly from the transmitter to the receiver to get reception
How are microwaves used by satellites?
- for satellite TV, the signal from a transmitter is transmitted into space
- it’s picked up by a satellite receiver dish orbiting above the earth
- the satellite transmits the signal back to earth in a different direction where it’s received by a satellite dish in the ground
- there is a slight time delay between the signal being sent and received because of the long distance the signal has to travel
its best to use microwaves which can pass easily through the earths watery atmosphere
how can microwave ovens use microwaves?
- the microwaves are absorbed by water molecules in food
- this transfers the energy they are carrying to the food molecules, causing the water to heat up
- the water molecules then transfer this energy to the rest of the molecules in the food by heating which cooks the food
How is infrared radiation used?
infrared cameras - can be used to detect radiation and monitor temperature, the camera turns the IR radiation into an electrical signal which is displayed on a screen as a picture, the hotter the object is, the brighter it appears
food can be cooked - the temperature of the food increases when it absorbs IR radiation e.g. from a toaster
electric heaters - contain a long piece of wire that heats up when current flows through it, this wire then emits lots of IR radiation (and a little visible light, the wire glows). the emitted IR radiation is absorbed by objects and the air in the room, transferring energy to by the IR waves to the thermal energy stores of the objects causing their temperature to increase
What are the uses of visible light?
Optical fibres
- optic fibres are thin glass or plastic fibres that can carry data (e.g. from telephones) over long distances as pulses of visible light
- they work because of reflection, the light rays are bounced back and forth until they reach the end
- light is not easily absorbed or scattered as it travels along a fibre
what are the uses of ultraviolet?
tanning beds - UV lamps are used to give people an artificial suntan (overexposure to UV radiation can be dangerous)
fluorescent lights - they generate UV radiation, which is absorbed and re-emitted as visible light by a layer of a compound called a phosphor on the inside of the bulb. they’re energy efficient so they’re good to use when light is needed for long periods
security pens - used to mark property with your name. under UV light the ink will glow, but it’s invisible otherwise. can help the police identify your property if it’s stolen
what is fluorescence?
a property of certain chemicals, where UV radiation is absorbed and then visible light is emitted
