The power of such sources is increasing, and we can now approach the ultimate diffraction limitation of beamwidth for light as for microwave radio. In the 1960s, coherent sources of light became available. The higher-order the reflection, the further the wave has travelled and the. Runnymede College of 56 (i) She uses a loudspeaker to send a sound wave of frequency 2. The fence behaves as a diffraction grating for sound waves. These waves are detected by the aerial in. Second order reflections are like shots played off two cushions, third order off three etc etc. The microwaves from the transmitter are polarised. You can imagine the waves bouncing around like balls on a pool table. Scientists have grown accustomed, however, to accepting another limitation on the angular width of a beam of light, and that is the angular width of the incoherent source. In small rooms, first order reflections tend to be loud and arrive very soon after the direct sound. Apertures in optical systems, on the other hand, are very rarely less than one hundred times the wavelength. The diameter of a radar antenna is somewhat greater than this, but rarely more than one hundred wavelengths in diameter. In dealing with sound waves, the aperture of a loudspeaker will not be more than a few wavelengths in diameter. The phenomena are essentially the same for light waves too, but these electromagnetic waves are shorter than radar waves and sound waves by a factor of about a million, and as a result the manner of observing the pattern tends to be different. Short radio waves such as used in radar have much the same wavelengths as audible sound waves, so that even the scale of the patterns is similar. Thus the diagrams and relations developed for sound waves are applicable to radio waves. Broadcasting Radio waves are good at broad casting (sending out to lots of receivers) and that is how we get to listen to radio and TV broadcasts. Diffraction phenomena are essentially the same for electromagnetic waves as for sound waves.
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