AS Physic Unit 2 Waves

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  • Waves
    • The nature of waves
      • Progressive wave
        • A pattern of disturbances travelling through a medium and carrying energy with it.
        • It involves the particles of the medium oscillating about equilibrium position.
        • It does not involve the transfer of matter.
      • Transverse Waves
        • Particle oscillations are at right angles to the direction of travel of the wave.
        • Example of a transverse waves is light.
      • Longitudinal waves
        • The particles oscillations are parallel to the direction of travel of the wave.
        • An example of a longitudinal wave is a sound waves.
      • Displacement - distance graph is a snapshot of the wave at a particular time.
      • A displacement-time graph follows the movement of one particle over a given time.
      • Characteristic
        • Wavelength
          • the minimum distance between two points on the wave oscillating in phase.
        • Frequency
          • the number of cycles of a wave that pass a given point in one second
        • Amplitude
          • distance from the middle of the wave to the crest
        • Speed
          • the distance traveled by the wave one second
      • Phase
        • The relationship between the pattern of vibration of two points on a wave.
        • Points oscillating in phase  will be multipliers of 360
        • Points oscillating in anti phase will be 180  out of phase.
      • Wave Equation
        • Speed = frequency x wavelength
          • Speed is in ms                   Frequency is in Hz               Wavelength is in m
      • Polarization
        • A transverse wave in which the particle oscillations occur in only one of the directions at right angles to wave propagation.
        • If you try to view polarized light through a second polarizer filter rotating 360  the what you would see would be alternating light and dark.
    • Wave poperties
      • Reflection
        • As the waves strike a plane barrier they are reflected. This is very similar to a beam of light reflecting on a plane mirror.
        • If a cruve barrier is used, the waves can be made to converge at a point. the angle of incidence is equal to the angle of reflection.
      • Refraction
        • the change in direction of a wave at a boundary between two materials. This is caused by the change in speed.
      • Diffraction
        • The spreading out of a wave when it meets an obstacle into regions where it would not be seen if it moved only in straight lines.
      • principle of Superposition
        • If the waves from two sources occupy the same region then the total displacement at a point is the vector sum of the displacements of the individual waves at that point.
        • there are two types of interference when this takes place. Constructive and Destructive interference.
          • Constructive Interference - if two waves arrive at a point in phase, have the same frequency and equal amplitude.
          • destructive Interference - if the peak of one wave arrive at the same time as the toughs fro the other. There will be a smaller amplitude and sometimes cancel out
        • Coherence
          • There is a constant phase difference and same frequency.
          • An example is a laser light.
      • Path Difference
        • A measure of the distance between two waves arriving at a point in terms of their wavelength.
        • If we consider the effect of superposition at many points, an interference pattern will develop showing areas with constructive and destructive interference.
        • if the path difference is S2P - S1P equals a whole number of wavelengths then the waves arriving at point P in phase will produce constructive interference
        • If S2P - S1P is equal to multipliers of half wavelengths then waves arriving in anti-phase at point P will produce destructive interference.
      • Young's Double Slit Experiment
        • Two light sources at the double slits are produce. Because these two light sources originate from the same primary source, they are coherent and create an interference pattern.
        • Bright fringes can be created when the diffracted waves overlap and are caused by constructive interference.
        • Dark fringes can also be created from destructive interference.
      • The diffraction grating
        • Its a plate on which there are a very large number of parallel, identical and closely spaced slits.
        • If monochromatic light is incident n this plate, a pattern of narrow bright fringes are produces.
        • As there are many slits, the bright fringes are extremely narrow, and usually much further apart than the double slit experiment.
        • dsin0 = n
          • d = slit width n= order        number           = wavelength 0 = angle
          • A very small d makes the orders much further apart and a large number of slits makes the beams much brights and sharper.
        • With white light
          • Each wavelength making up the white light is diffracted differently. Red is diffracted the most and violet is diffracted the least.

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