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25 Cards in this Set
- Front
- Back
- 3rd side (hint)
Transverse waves |
Oscillations are perpendicular to the direction of energy transfer (wave movement) |
Electromagnetic waves (vibrating electric and magnetic fields) Secondary seismic waves |
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Longitudinal waves |
Oscillations are parallel to the direction of energy transfer (wave movement) |
Sound (alternating compressions and rarefactions of the medium) Primary seismic waves |
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Cycle |
One complete oscillation of a point on the wave |
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Displacement |
Distance and direction of a point on the wave away from its equilibrium position |
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Amplitude |
Maximum displacement of a point on the wave away from its equilibrium position |
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Wavelength |
Distance between a point on a wave and the same point on an adjacent wave |
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Period |
Time taken for a complete wave to pass a given point |
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Frequency |
Number of complete waves passing a given point per second / number of cycles per second |
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Phase |
Distance of a point along the wave as a fraction of the wave cycle The fraction of the wave cycle that as oscillating particle has completed since the start of the wave cycle |
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Phase difference |
The distance between 2 oscillating points on a wave as a fraction of the wave cycle Phase difference of 0 = in phase Phase difference of 180° or π = out of phase |
Measured as as angle or fraction of the wave cycle |
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Polarisation |
A wave is polarised if the oscillations are in the same plane. Unpolarized waves consist of oscillations in many different planes. A polarizing filter filters unpolarised waves by only allowing through oscillations parallel to the slits and blocking out oscillations in other directions. Polarisation can only happen for transverse waves as the oscillations occur in different planes to the direction that the wave is moving. |
Polaroids reduce the intensity of light that passes through them, so are used in sunglasses and cameras to reduce glare from light reflected off of water or glass. Radio waves from a transmitter are polarised, so aerials of radio receivers must be aligned in same plane for best reception. |
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Mechanical waves |
Oscillations of the particles of the medium transfer energy as the wave progresses through the substance |
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Electromagnetic waves |
Oscillating electric and magnetic fields which propagate through space without the need for a medium |
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2 Polaroid filters |
If unpolarised light is passed through 2 Polaroid filters, the transmitted light intensity changes as one filter is rotated relative to the other. When one filter is at 90° to the other, they are crossed and transmitted light intensity is at a minimum as polarised light from the first filter can't pass through the second filter. |
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Wavefronts |
Points along the wave with constant phase Direction in which wave travels is perpendicular to wavefronts |
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Refraction |
When waves cross a boundary between media of different optical densities, wave speed changes , causing the wavelength to change. If the wavefronts approach at an angle to the boundary, they change direction |
Frequency doesn't change |
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Diffraction |
When waves spread out after passing through a gap or around an object. Each point along the wavefront can be considered to be a secondary emitter of wavelets, which combine to form a new wavefront which spreads beyond the gap or around the object |
Narrower gap and longer wavelength gives greater spread |
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Superposition |
When 2 waves meet and pass through each other, they combine such that the total displacement at a point is equal to the sum of the individual displacements at that point |
Constructive interference: Crest + crest = reinforcement = supercrest = max positive displacement Trough + trough = reinforcement = supertrough = max negative displacement Destructive interference: Crest + trough = cancellation: ● if the same amplitude - resultant displacement is 0 ● if different amplitudes - resultant displacement is minimum |
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Interference |
When waves continuously pass through each other at constant frequency and with constant phase difference, reinforcement and cancellation occur at fixed positions, producing an interference pattern. |
Occurs when coherent sources of waves pass through each other. Light from lamps isn't coherent, so reinforcement and cancellation occur at random positions, so an interference pattern won't form |
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Stationary waves |
Formed when two progressive waves of the same frequency pass through each other in opposite directions: ▪when in phase, reinforcement occurs ▪when out of phase 1/4 of wave cycle later, cancellation occurs No energy is transferred in a freely vibrating stationary wave. Consists of nodes and antinodes at fixed positions. All points on stationary wave, except at nodes, oscillate at same frequency. Phase difference between 2 oscillating points on stationary wave = mπ (m is no. of nodes between points) |
Nodes = points on the wave with no displacement/0 amplitude Antinodes = points on the wave with maximum displacement/amplitude |
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Stationary waves on a vibrating string |
Nth harmonic pattern of vibration = forms a stationary wave pattern = n number of antinodes Stationary wave patterns occur at frequencies of F1, 2F1, 3F1... L = length of vibrating section of the string Each loop = half λ Pitch = frequency |
■ λ is equal to different amounts of L and using f = c/λ, rearrange ■ c = √(T/μ) and combine with previous formula |
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Progressive waves |
Waves that transfer energy |
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Light sources |
Filament lamp/ sunlight contains range of wavelengths and isn't coherent as atoms emit photons at random so they have random phase differences. Laser light is highly monochromatic (very specific wavelength) and a coherent source of light, as atoms emit photons in phase with each other, so can be used to illuminate double slits directly without need for single slit |
Power of Laser beam is concentrated in very small area, so it's very dangerous to eyes as the eye lens would focus it to a single spot and destroy the retina |
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Coherence |
Waves have same frequency and constant phase difference Coherent sources emit waves with the same frequency and constant phase difference A single slit ensures that light from a non coherent source becomes coherent once it reaches the double slits |
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White light fringes |
Fringe spacing depends on wavelength of the light used. ■White light consists of a range of wavelengths of light, and each wavelength produces it's own interference pattern. ■The central fringe of each pattern is in the same position on the screen, so the central fringe is white. ■The inner fringes have blue on the inner side and red on the outer side as the red fringes are more spaced out than blue fringes and so they don't overlap. ■The outer fringes become fainter and different wavelengths of light merge and reinforce each other. |
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