Waves Pt. 1

Waves Pt. 1

1. Progressive Waves

   • Wave Speed
     • The speed of a wave is calculated by frequency x wavelength (c = fλ).
     • The speed of sound can be measured using two microphones in a straight line, with a distance of "d" between them. The microphones should have separate inputs so the signals from each can be recorded separately.
       • Use the signal generator to produce a sound from the loudspeaker and use the computer to record the time between the first and second microphone picking up the sound. Do this by measuring the time delay between the first peak of the signal received by each microphone on a graph of voltage against time. you can then use speed = distance / time to calculate the speed of the sound waves.
   • Definitions
     • Amplitude - The greatest displacement from the equilibrium position of a particle in the medium through which the wave travels.
     • Frequency - The number of wave oscillations per second. Frequency = 1 ÷ T, where T = periodic time.
     • Wavelength - The distance between corresponding points in successive waveforms. These points are in phase.
     • Displacement - How far a point on the wave has moved from its equilibrium position.
     • Phase - Behaviour of wave particles at any instant in comparison with other wave (or other particles). Phase Difference is the amount by which one wave lags behind another wave. Phase difference can be measured in angles or fractions of a cycle.
     • Period - Time taken for one whole wave cycle to be completed.
     • A wave is caused by something making particles or fields oscillate (or vibrate) at a source. These oscillations pass through the medium as the wave travels, carrying energy with it. A wave transfers this energy away from its source - so the source of the wave loses energy.
     • Reflection - The wave is bounced back when it hits a boundary.
     • Refraction - The wave changes direction as it enters a different medium. The change in direction is a result of the wave speeding up or slowing down.
   • A progressive wave consists of a disturbance moving from a source to surrounding places as a result of which energy is transferred from one point to another. Put simply, a progressive wave carries energy from one place to another without transferring any material. The vibrations of the particles in a progressive wave are of the same amplitude and frequency. But this phase of the vibrations changes for different points along the wave.

2. Transverse and Longitudinal Waves

   • Transverse - The direction associated with the disturbance is at right angles to the direction of travel of the wave. Examples: waves plucked on strings, waves on water, EM Waves.
   • Longitudinal - Vibrations in this wave occur in the same direction as the wave's direction of travel. Displacements of particles cause compressions and rarefractions. Most common example of a longitudinal wave is sound.
   • Polarisation
     • A transverse wave is oscillating in all directions. It passes through the first slot, which only allows oscillations in the vertical plane. The transmitted wave from this slot is plane polarised. The next slot only allows oscillations in the horizontal plane. Therefore, the wave is unable to pass through this slot. The two slots are therefore crossed.
     • Longitudinal waves would emerge from both slots whatever their relative position, so only transverse waves can be polarised.
     • Polarisation in the real world - When light is reflected off some surfaces, it can cause glare, as they are partially polarised. Therefore, if you view the light with polarising filters at the right angle, some of the reflected light can be blocked out. This ultimately reduces the intensity of light entering the eye. This is used in polaroid sunglasses and in photography.
     • When radio waves are transmitted, they are polarised. An aerial is used as part of a radio receiver and this must be aligned in the same plane as the incoming radio waves to get the best reception.

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