Waves and Vibrations

• Phase is the fraction of a wave cycle that has elapsed relative to a given origin.
• Phase difference is the difference in the fraction of a cycle that has elapsed between two waves, measured in radians (rad.) One cycle is equal to 360 degrees or 2π.
• Amplitude is a wave's maximum displacement from its equilibrium position, measured in metres, m
• Frequency is the number of waves that pass a point in a unit time period. It is the inverse of the time period (1/t).
• Wavelength is the distance between two identical positions on two adjacent waves. It is commonly measure from peak to peak or trough to trough.
• Electromagnetic waves are oscillating electric and magnetic fields that progress through space without the need for a substance. The vibrating electric field generates a vibrating magnetic field, which generates a vibrating electric field further away, and so on. Electromagnetic waves include radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma radiation.
• Progressive waves carries energy from one place to another and are a specific type of mechanical wave, as they involve the transfer of energy through the oscillation of particles in a medium.
• Longitudinal waves are waves in which the energy transfer in the wave travels parallel to the direction of propagation of the wave.
• Transverse waves are waves in which the energy transfer occurs perpendicular to the direction of propagation of the wave.
• All electromagnetic waves travel at the same speed in a vacuum.
• Polarisation is a phenomenon exclusive to transverse waves. Polarisation is evidence of transverse nature as transverse waves can oscillate in any plane, and polarisation is the process in which the waves are made to oscillate in one plane only.
• Polarisation is done by passing the waves through a grid so that only waves in the correct plane can pass through. Longitudinal waves cannot be polarised.
• Transverse waves are plane-polarised if the vibrations stay in one plane only. If the vibrations change from one plane to another, the waves are unpolarised.
• Light from a filament lamp or a candle is unpolarised. If unpolarised light is passed through a polaroid filter, the transmitted light is polarised as the filter only allows through light which vibrates in a certain direction, according to the alignment of its molecules.
• If two polaroids are placed with their axes crossed (at right angles), no light will get through because there is no component of electric field parallel to either axis.
• The angle between the directions of maximum transmission of two polaroids is called the relative retardation.
• Polarisation is used in polaroid glasses, where it attempts to reduce the amount of light reaching the eye by polarising the light. Also it can be taken into account when transmitting and receiving waves, an aerial has to be aligned to the plane of the polarised waves for it to receive maximum signal.
• Mechanical waves are a type of waves that pass through a substance. When waves progress through a substance, the particles of the substance vibrate in a certain way which makes nearby particles vibrate in the same way, and so on.
• One complete cycle of a wave is from maximum displacement to the next maximum displacement.
• The period of a wave is the time for one complete wave to pass through a fixed point
• The phase difference in radians equation: (2pi * diameter)/wavelength

  
• Coherent waves mean that the waves will have the same wavelength, frequency and a fixed phase difference between them.