70, 74, 80

70, 74, 80

1. A diffraction grating is a flat plane object. It has a series of regular lines formed on it that block parts of an advancing wavefront.

2. Diffraction = the bending of waves around the corners of an obstacle into the region of geometrical shadow of the obstacle

3. Superposition – is the adding together of wave displacements that occurs when waves from two or more separate sources overlap at any given location in space. The displacements simply add mathematically.

4. Path difference – is the difference in length between two (straight line) rays, e.g. one from a particular grating gap to a given point in space and the ray from the next-door grating gap to the same point.

5. Interference pattern – a stationary pattern that can result from the superposition of waves travelling in different directions, provided they are coherent. Coherent

6. Coherent – literally means ‘sticking together’ and is used to describe waves whose superposition gives a visible interference pattern. To be coherent, waves must share the same frequency and same wavelength and have a constant phase difference

7. Stationary waves

   • In a stationary wave (or standing wave) energy is stored rather than transferred to other locations.
   • Resonance – the storing of energy in an oscillation or a stationary wave, the energy coming from an external source of appropriate frequency.
   • Both stringed and wind instruments depend on resonance to produce their musical notes. In a stretched string, the oscillations are transverse, and the speed, v, at which waves travel down
   • Oscillations of different amplitudes occur along the length of the wave in a pattern that does not change over time.
   • Radio and TV antennas have a reflector element that bounces the incoming waves back and creates a stationary wave pattern. The detector is placed at an antinode position for the particular wavelength of radiation the aerial has been designed to pick up.
   • In microwave ovens, stationary wave patterns caused by reflections for the metal sides of the oven with hot and cold spots corresponding to antinodes and nodes.
   • Optical fibres
     • Broadband is used as a relative term to indicate the speed and carrying capacity of a data cha
     • Multimode fibre is the standard fibre cable used for sending optical signals over short to medium distances – for example, connections to instruments, jumpers in cabinets, small local area networks
     • Single mode fibre has an even narrower core (8 μm to10 μm), which is less than ten wavelengths of the infra-red light that is used in them
     • Analogue signal – a signal whose strength is proportional to the quantity it is representing
     • Digital signal – conveys in binary code a number that represents the size of the measured quantity.