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Edexcel A level Physics topic 5 waves and nature of light notes summary (A*)
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Concise summary of key points based on syllabus points, mark schemes, study guides and textbooks. (A* physics grade)
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,, KEY TERMS
Progressive waves: transfer of energy from one place to another without transferring any material; in the
same direction as direction of wave travel.
Longitudinal wave - particle motion is parallel to direction of energy
transfer. E.g. soun
Transverse wave - particle motion is perpendicular to direction of energy
transfer. E.g. electromagnetic
displacement (m) - distance of a particle from its equilibrium position
Amplitude (m) - maximum displacement of a vibrating particle or wave from its equilibrium position
Period (s) - time taken for one complete oscillation.
Frequency (Hz) - number of complete oscillations per second
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Phase (degrees / radians)- position of a certain point along the wave cycl
Phase difference - difference in vibration between two points of a wave at a single point in tim
Path difference ( /m) - difference in length of the distances from their sources and the point of interferenc
Wave speed (m/s) - speed at which the energy is transmitted.V=wavelength / perio
Coherent - waves with a constant phase relationship / that have the same wavelength and frequency and a
constant phase difference
Wavefront - line / surface in a wave in which all points are in phase
Principles of superposition - when two or more waves meet at a point, the resulting displacement is the
vector sum of the individual displacement of the wave
Interference - when 2 or more waves superpose at a point, there’s a change in overall intensity /
displacement
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Stationary / standing waves - superposition of two progressive
waves with the same wavelength moving in opposite directions
Node - when amplitude is zero; distance between nodes is 1/2 λ
Antinode - point on a stationary wave where the incoming and
re ected wave are in phase forming a maximum poin
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Diffraction - spread of a wave as it passes through / around a ga
Refraction - when a wave changes speed when it crosses the boundary into a new medium
Refractive index - A measure of how much the speed of light changes between two different medi
Critical angle (c) - angle of incidence when the angle of refraction is exactly 90 ; when refracted ray travels
along the boundary line
Total internal re ection - When the angle of incidence is greater than the critical angle and the ray re ects
at the surface and remains within the medium
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, Power - measure of a lens’ ability to bend light
Real image - When rays of light have actually converged to produce an image that can be projected onto a
screen
Virtual image - When rays of light only appear to have converged but can’t be projected onto a screen
Polarised wave - transfer waves in which oscillations occur in a single plan
Focal point - point where parallel rays of light meet or appear to diverge fro
Focal length - distance between optical centre of lens and the focal poin
Principle axis - line that passes normally through the optic centre of the len
Optical centre - point through which rays of light will pass without deviation
Equations
Angle in radians = π/180 x angle in degrees | Angle in degrees = 180/π x angle in radian
F = 1/T | Frequency = 1/perio
V = fλ
Phase difference:
Δx = path difference; Δϕ= phase difference
Distance between adjacent maxima / minima = λ /
Speed of Transverse wave on a string:
v = speed, T = tension in string, u = mad per unit length of strin
Intensity of radiation:
I = P/A; P = power, A = amplitude
Critical angle
Sin c = 1/
Magni cation
m = image height / object height = v/
Diffraction grating
d sinθ = nλ
d = distance between slits, θ = angle to the normal from 1st order, n = order, λ = wavelengt
Refractive index:
- higher RI - more optically dens
Photon energy
E = hf / E = hc/λ
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,Waves
Wave Graphs
Displacement-Distance Displacement-Time
Each point represents a separate wave particle Represents di erent positions of one wave particle
Particles can only move up or down
Electromagnetic waves
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, Superposition and coherence
• Superpositio
Constructive
- when waves meet in phase and produce a wave with maximum resultant amplitude
- As intensity ∝ (amplitude)², increase amplitude = louder sound &
brighter ligh
-path difference = nλ; phase difference = 2π radian
Destructive
- Waves meet in antiphase and produce a wave with minimum / zero
resultant amplitud
- Path difference = (n + 1/2) λ; phase difference = (2n + 1) π radian
- Used for active noise cancellation
• Interferenc
- Two sources can produce a pattern of maxima and minima, where the waves combine constructively /
destructively at xed position
- Stable interference patterns only occur if
- Waves are the same typ
- Sources are coheren
- Waves have similar amplitude at point of superpositio
• Phase difference (degrees / radians):
- In phase - when two particles are both at the same point in the wave cycle, and have the same
displacement and velocity; phase difference = 0 / multiples of 360
- Out of phase - when one particle reaches its maximum positive displacement at the same time as the
other reached its maximum negative displacement; phase difference = odd-number multiples of 180º /
π radians
• Path difference (metres):
- Difference in distance travelled by two waves
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