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Chapter 11 - Coggle Diagram
Chapter 11
Terminology
displacement, s (m)
distance from the equlibrium position in a particular direction, vector so can have +ve or -ve value
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wave speed, v or c (ms^-1)
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wavelength, λ(m)
minimum distance between two points in phase on adjacent waves, e.g. distance between one peak to another
period of oscillation, T (s)
time taken for one oscillation or time taken for wave to move one whole wavelength past a given point
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Refraction
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sound waves normally speed up when they enter a denser medium, whereas electromagnetic waves normally slow down
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polarisation
polarisation means that the particles oscillate along one direction only (e.g. up and down in the vertical direction
this means that the wave is confined to a single plane and this 'plane of oscillation' contain the oscillation of the particles and the direction of travel of the wave
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light from an unpolarised source like a filament lamp is made up of oscillations in many possible planes
these oscillations are always at 90 degrees to the direction of energy transffer as light is a transverse wave
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longitudinal waves cannot be polarised as the oscillations are always parallel to the direction of energy transfer
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Diffraction
is a property unique to waves. When waves pass through a gap or travel around an obstacle, they spread out
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speed, wavelength and frequency of a wave do not change when diffraction occurs
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Electromagnetic waves
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Do not need a medium unlike all other waves, so can travel through a vacuum
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EM wave can be reflected, refracted, and diffracted like all waves.
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Progressive waves
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Transverse waves
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have peaks and troughs where to oscillating particles are at maximum displacement from their equilibrium position
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Intensity
As a progressive wave travels from its source, it spreads out. the energy and power transferred becomes less concentrated.
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in the case of light from the andromeda galaxy for example, the drop in brightness can be used to calculate how far the source is from the reciever.
intensity of a progressive wave is defined as the radiant power passing through a surface per unit are
I = P/A
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radiant power passing through the surface, P (W)
cross sectional area of the surface, A (m^2)
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Phase difference
describes the difference between the displacements of particle along a wave, or the difference between the displacements of particles on different waves.
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if particles are oscillating perfectly in step with each other, they are described as in phase.
phase difference of zero
when they are separated by whole wavelengths. i.e. 360 degrees, 720 degrees, 2pi radiants, 4 pi radians etc
if particles are completely out of step with each other, then they are in antiphase. Phase difference of 180 degrees or pi radians
Reflection
occurs when a wave changing direction at a boundary between two different media, remaining in the original medium
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when waves are reflected, their wavelength and frequency do not change
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we can see this from this wavefront diagram representing the series of wavefronts which can be thought of as the peak of each ripple
therefore, the distance between each wavefront is the wavelength.
when circular waves reflect off surfaces, their wavelength and frequency remains the same just like plane waves
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