# physics

waves transfer energy but not matter
energy is transferred by oscillations in the material which the wave is travelling through
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osciallation - repetative movement back and forth a central point
amplitude - hight of the wave from point of displacement
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wave length - from trough to trough (distance of oscillation)
frequency - number of waves passing any point (measured in hertz Hz) = 1s (1 wave per second = 1 Hz
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time period - amount of time it takes for 1 wave to pass a point
f = 1/t or t=1/f
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transeverse waves
oscillation at right angles perbendicular to direction of travel
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waves on a string/wire
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longitudinal waves
oscillations occur parallel to direction of travel e.g sound waves
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speed = frequency x wave length
wave speed (m/s) frequency (Hz) wavelength (M)
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electrmagnetic waves travel at 3x108 m/s through a vaccume
rarefraction - light changing direction as it enters a different material
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waves pass from one medium to another there is a change in speed
if the waves approach the interface between media at an angle this also causes a change in direction called rarefraction
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refracted index
rafracted index is a ratio the the speed of light in a vaccume to the speed of light in the material
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n = c/v (n-refracted index, c-speed of light in a vaccume,v-speed of light in a material)
snells law - the relationship between angle and refractive index
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n = sin (i) / sing (r)
critical angle - n = 1 / sin C (refractive index = 1 / sin (critical angle)
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when waves meet the interface between two media some of those waves will keep going, they are absorbed
if they continue to travel thenn they can be said to be transmitted by the new medium e.g sound waves passing through air then water
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waves that reduce in amplitude as are transmitted are ATTENUATED
reflected waves will bounce off of the interface between two media
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the angle of reflection is equal to the angle of incidence
fibre optics
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the reason light is transmitted through an aptical fibre is because the fibre is denser than its surroundings
the difference in density allows total internal reflection to take place
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core - glass or plastic with higher index of refraction than the cladding. - carries the signal
cladding - glass or plastic with a lower index of refraction than the core
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buffer - protects fibre from damage and mositure
jacket - holds one or more fibres in place
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em spectrum
the range of frequencies of electromagnetic radiation
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infared light - anything with temperature, tv remote/night vision cameras, burns
ultra violet - very hot objects, tanning/production of vitamin D in the skin, sun burns
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x-rays - pass through solid objects, medical/scanning luggage, can cause cancerous cells
gamma rays - have a shorter wavelength than x-rays, pass through solid objects, kills cancer cells/medical, radiation
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ionising radiation can break molecules into ions (ionisation) this occurs if photons have enough energy
microwaves - wavelengths longer and frequencies lower than infared, communications, cataracts
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radio waves - have the longest wave lengths and the lowest frequencies of thr EM spectrum
what is optical fibre
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a transmitter is responsiable for converting an electrial digital signal into a light signal by changing its density and pulse rate
if the ray has to travel a long distance it will have to pass through an optical regenerator which re-boosts the strength of thr ray by copying the message and sending a duplicate onward to its destination
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finally the ray of light with the message imprinted on its arrival the optical reciever here it is decoded back into a binary digital format
analogue or digital?
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fibre opticts use digital siganls. speaker cables use analogue signals
analogue signals that change in size with the physical quantity they represent
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optical fibres are used in: telecommunications, broadband internet networks, cable television, endoscopy
optical fibres are better than copper wires because optical fibre signals;
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have lower losses so travel further before needing amplications
secure so cannot be tapped into
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higher frequencies so greater bandwidth
we dont use copper because it costs more and needs specialist installment
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bandwidth - a mesaurement of distinct signals at different frequencies the network can carry
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fibre opticts - allow very high bandwidth networks using them are called broadbands
wave phases
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when waves pass through eachother they do not damage eachother. the net displacement of the medium that they travel in at any point in space or time, is the sum of individual wave displacement this displacement is called net superposition
phase difference - the difference in cycle position between two waves this difference is normally given as a phase angle
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coherent waves - waves with the same frequency and constant phase difference
wave fronts - lines joining points on waves that are all in phase (they are one wavelength apart from eachother may also be planes in 3D)
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the principle of superposition
interference is a detectable pattern of different strengths (amplitudes) of wave oscillation e.g large and small ripples, loud and soft sounds
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it is caused by waves from different sources crossing and adding together that is superposition
interface
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when 2 waves pass through eachother they interfere to create a super position of the waves
when both waves have a positive displacement or both have a negative displacement the magnitude of the displacement will be increased. this is called constructive interference
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when one wave has a positive displacement and the other a negative displacement the magnitude of the displacement will be decreased. this is called destructive interference
diffraction
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diffraction - waves spreading out as they go through gaps
for the largest amont of diffraction through a gap, the gap width should be the same as the wavelength of the wave
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explaning two source interference
to produce dark and bright interface fringes : a path difference is created by dividing a light source so that rays of light travel at different paths
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the difference is a whole number of wavelengths (nλ )the rays will be in phase and constructive interface - bright fringes occur
dark fringes occur halfway between the bright fringes where destructive interference takes place
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diffraction patterns
diffraction patterns - occur when light passes through a narrow slit. this is due to interface
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when there are more slits there is a greater space between the bright maxima and dark minima
emission spectra
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the path difference will be different and different angles from the light source
different wave lengths of electromagnetic waves are refracted at slightly different angles so they separate out
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spectra
when light has a mixture of wavelengths, the condition for constructive interface occurs at different angles for each wave length
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so a set of coloured light spectra is produced rather than just a set of fringes
emission spectra
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photons - particles of light, each photon is a packet of energy with a corresponding frequency and wavelength
the energy of a photon is directly proportional to its frequency
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E = H X F
E - energy H - planks constant (6.63 x 10-34) F - frequency of radiation
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analogue or digital
digital: infomation enclosed as a series of numbers
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1. a sensor is connected to an ADC input, 2. the sampeling rate and sensitivity are selected, 3. a digital signal is sent to a display or data storage device
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can be sorted and processed by computer, more data fitted in the sam band width, most interference can be eliminated giving higher quality
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data accuracy limited by sampeling settings, time delay due to signal processing
stationary waves
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stationary or standing waves can be thought of as two progressive waves moving in opposite directions and super imposed onto eachother, the result is a fixed pattern of niodes/antinodes
nodes: part of a wave which dosent move
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antinodes: part of a wave which moves the most
standing waves are waves that store energy rather than transfering it. when progressive waves move in opposite directions they pass through eachother, they can interfere to create a wave that does not move
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the position that does not change in on this wave are its nodes
the position where peak/trough appear on this new wave are its antinodes
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number of antinodes, how many wavelengths in L
1 - L = λ /2, 2 -L=2 λ /2 = λ, 3 - L=3 λ /2, 4 - L4 λ /2
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on a string of specific length and mass many different standing waves can form each with their own : wave form, wavelength, frequencies, number of nodes and antinodes
these called harmonic modes of vibration (ways of vibrating) and harmonic frequencies
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stringed instruments
the fixed ends of the sting are always nodes, the fundamental mode has one, antinode so L = λ /2
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for higher harmonics any number of N antinodes can fit in the length of the string so L = λ /2N
wave speed on a string = √ T/U (T is tension, U is mass per unit length in KG/M)
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musical instruments, why do standing waves form?
waves moving in opposite directions can interefere to cause standing waves. this will happen when a wave is reflected back on itself. this happens in muscial instruments
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resonators
resonators store energy by reflecting the wave back on its self to form a stationary wave pattern, they will only efficiently recieve energy from an external source that has freqency close to their own natural frequencies; this is called resonance
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they have a fundamental (lowest) natural mode of oscillation and higher harmonics
natural frequencies
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all objects have natural frequencies, these are the frequencies that they will oscillate at best. these frequencies correspond to the wavelengths that fit on the objects like the standing waves that fit on a string
waves in communication
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short range
wifi, bluetooth and infared are considered to be short range communication types.
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wifi has a range of between 10 and 100m depending on the transmitter and reciever, bluetooth is limited around 10m, infared is just a few meters
long range
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satellite communications, mobile phones are considered long range
mobile phones communicate with transceiver towers no more than a few km away
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the area within which a tower can recieve a signal is called a cell, hence cell tower
signals can be sent to satilites from ground stations allowing them to be sent round the world
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networking
by linking devices together and transferring infomation between them communications can reach much further this is called networking
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mobile phones are networked together with cell towers to reach accross a country
satellites are networked to allow for satellite communication around the world
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bluetooth and infared however are not networked together and only work device to device
hand shaking
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short messages are sent back and forwards between devices to allow them to recoginise eachother and set up communication parameters
mobile phones handshake as they switch cell towers, bluetooth devices handshake when they connect
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handshaking also stops infomation getting lost or jumbled by ackknowledging when a message has been recieved
transmitting and recieving different frequencies
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a transceiver transmits and recieves signals, mobile phone transcievers transmit and recieve at different frequencies. they do this to avoid interference
satellites also recieve communications at one frequency then transmits at another. this is done via a trasponder unit which also filters noise from and amplifies the signal
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trasnponder unit which also filters noise from and amplifies the signal
bluetooth devices change frequencies often limits interference with wifi. this is done as wifi operates at fimilar frequencies
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## Other cards in this set

### Card 2

#### Front

amplitude - hight of the wave from point of displacement

#### Back

osciallation - repetative movement back and forth a central point

### Card 3

#### Front

frequency - number of waves passing any point (measured in hertz Hz) = 1s (1 wave per second = 1 Hz

f = 1/t or t=1/f

### Card 5

#### Front

oscillation at right angles perbendicular to direction of travel