imaging + signalling Flashcards
how is most information transferred?
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by waves
what are some examples of information being transferred by waves?
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some examples are:
• scientific imaging
• remote sensing (infrared)
• heat cameras (infrared)
• communications
• data streaming
where does the wave transfer energy to?
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wave transfers energy away from its source
what does a progressive wave do?
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a progressive (moving) wave carries energy (+ usually information) from one place to another without transferring material
how can you tell if a wave is carrying energy?
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ways to tell if a wave is carrying energy:
• em waves can cause things to heat up
• x-rays + gamma rays knock electrons out of their orbits, causing ionisation
• loud sounds make things vibrate
• wave power can be used to generate electricity
what happens when waves carry energy away from their source?
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since waves carry energy away from their source, source of wave loses energy
what parts of a wave do you need to know?
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you have to know these parts of wave:
• displacement, x
• amplitude, A
• wavelength, λ
• time period, T
• frequency, f
• phase difference
what is definition + units for displacement, x
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displacement is how far point on wave has moved from equilibrium/resting point
units: metres, m
what is definition + units for amplitude, A
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amplitude is maximum displacement of wave from its equilibrium/resting position
units: metres,m
what is definition + units for wavelength, λ
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wavelength is distance from one point on wave to equivalent point on next consecutive wave
units: metres, m
what is the definition + units for time period, T
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time period is the time taken for one whole oscillation (of a wave)
units: seconds, s
what is the definition + units for frequency, f
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frequency is the number of whole oscillations passing a given point per second
units: hertz, Hz or per second, s^-1
what is the definition + units for phase difference
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phase difference is the amount by which one wave lags behind another wave
units: degrees or radians
what is the relationship between the frequency + time period?
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frequency is inverse of time period
f = 1/T
what is equation for frequency?
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f = 1/T
therefore 1 Hz = 1 s^-1
what equation links wave speed, frequency + wavelength
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the wave equation
what is the wave equation?
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wave speed = frequency x wavelength
v = f x λ
what is a feature of all electromagnetic waves?
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all electromagnetic waves are transverse waves
what is a transverse wave?
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a transverse wave is a wave where the direction of oscillation is perpendicular to the wave’s direction of travel
what are the two main ways of drawing traverse waves?
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the two main ways of drawing transverse waves are:
1) displacement against time graphs
2) displacement against distance graphs
what are the features of a displacement against distance graph for a transverse wave?
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what are the features of a displacement against time graph for a transverse wave?
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why should you be careful when looking at displacement-distance and displacement-time graphs for transverse waves?
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both displacement-distance and displacement-time graphs give the same shape, so check label on x-axis to figure out which one it is
are all waves transverse?
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NO
eg) sound is a longitudinal wave
what are longitudinal waves?
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longitudinal waves are waves where the oscillations are parallel to the direction of the waves travel
what are the definition + units for intensity?
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intensity is the rate of flow of energy per unit area perpendicular to the direction of travel of the wave
units: Watts per square metre, W m^-2
what is the equation for intensity?
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intensity = power/area
I = P/A
what would intensity be a good measure for in real life?
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the amount of light energy that hits your retina per second
what is a simple definition for intensity?
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intensity is the measure of how much energy a wave is carrying
when does refraction happen?
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refraction happens when a wave changes speed at a boundary between two mediums
what exactly happens to a wave’s/ray’s energy when it meets a boundary between two mediums?
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when a wave/ray meets a boundary between two mediums, some of it’s energy is reflected back into the first medium and the rest of the energy is transmitted through into the second medium
what happens when light meets a boundary between two mediums at an angle to the normal?
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when light meets the boundary at an angle, the TRANSMITTED light is bent - “refracted” - as it travels at a different speed in each medium
what happens if light is transmitted through a very optically dense material?
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• the more optically dense a material is, the more slowly light travels in it
• so if light travels through a very optically dense material, light will slow down A LOT
what does the amount of refraction depend on and what does this mean?
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• the amount of refraction depends on the λ of the light
• this means that the focal length for a given lens will change depending on the λ of light passing through it
what does a converging lens do?
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a converging lens changes the curvature of wavefronts
how do lenses change the curvature of wavefronts?
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lenses change the curvature of wavefronts by adding curvature to waves via refraction as they pass through the lens
(converging lens adds positive curvature, convex lens adds negative curvature)
what happens to waves that are initially uncurved (+ are also parallel to the lens axis) as they pass through a converging lens?
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if a wave has zero curvature before passing through a converging lens (and the wavefronts are also parallel to the lens axis), the wave will be given a spherical curvature, centred on the focal point of the lens
how does a converging lens curve the wavefronts passing through it?
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a converging lens curves the wavefronts by slowing down the light travelling through the middle of the lens more than the light travelling through the lens’ edges
how long does it take for points on a wave to reach the focus point of a lens?
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all points on a wave take the same amount of time to get to the focus point of the lens
what is the focal length of a lens?
the focal length is the distance between the lens [axis] and the focus of the lens
what are the different ways of showing lens diagrams?
you can show lens diagrams in the following two ways:
• lens diagram using wavefronts
or
• lens diagram using rays (aka ray diagram)
example of lens diagram using wavefronts:
example of ray diagram
what happens as the power of the lens increases?
the more powerful (thicker) the lens, the more it will curve wavefronts that travel through it, so the shorter the lens’ focal length
what is the focus [aka focal point] of a converging lens?
the focus of a converging lens is the point where all the wavefronts that have passed through the lens converge
what is the equation for lens power?
lens power = 1/focal length
P = 1/f
when working out the power of a lens, the focal length HAS to be in METRES
what is the power of a lens + the units for it?
the power of a lens is the amount of curvature added by the lens to a wave passing through the lens
units: dioptres
what is the equation for the curvature of a wave?
curvature of a wave = 1/radius of wave’s curvature
curvature = 1/r
what is the relationship between the curvature added to a wave by a lens and the thickness of the lens?
the thicker the lens, the more curved its sides and so the more curvature the lens adds to the wave
what can you use the lens equation for?
you can use the lens equation to find where an image will be formed
what does the lens equation link together?
the distances between the lens, the image and the source of light
what is the lens equation?
the lens equation:
1/v = 1/u + 1/f
where:
* v = image distance (the distance between a lens and the image)
* u = object distance (the distance between a lens and the object (object == “light source”)
* f = focal length (the distance between a lens and it’s focal point)
showing the lens equation using a ray diagram:
what does the lens equation assume?
the lens equation assumes that the lens is thin