Coherence (physics) facts for kids
In physics, two wave sources are perfectly coherent if they have a constant phase difference and the same frequency, and the same waveform. In such a case the waves plot as identical: their peaks and troughs occur at the same time, and they have the same amplitude.
The idea has several distinct concepts. These are limiting cases which never quite occur in reality. However, they allow an understanding of the physics of waves, and have become an important concept in quantum physics.
More generally, coherence describes all properties of the correlation between physical quantities of a single wave, or between several waves or wave packets.
Images for kids
Figure 3: The amplitude of a wavepacket whose amplitude changes significantly in time τc (red) and a copy of the same wave delayed by 2τc(green) plotted as a function of time t. At any particular time the red and green waves are uncorrelated; one oscillates while the other is constant and so there will be no interference at this delay. Another way of looking at this is the wavepackets are not overlapped in time and so at any particular time there is only one nonzero field so no interference can occur.
Coherence (physics) Facts for Kids. Kiddle Encyclopedia.