# Standing wave

1. Mar 31, 2007

### adiputra

why there is a need to supply energy to maintain a standing wave?

2. Mar 31, 2007

### adiputra

sorry i think it is not quiite clear this is the full question. one end of a cord is attached to a vibrator while the other end is attached to a fixed position. a standing wave is resulted.althought energy is not transmitted by a standing wave, the vibrator must still provide power. Why is this?

3. Apr 1, 2007

### lpfr

A standing wave does not need to be supplied in energy to maintain its amplitude but for the losses of energy due to radiation and other causes.
Depending on the kind of wave and the "container" (string, EM cavity, drum skin, etc) and the coupling with the exterior, a standing can have heavy or almost zero losses. En electromagnetic wave in a superconducting cavity can have Q of the order of $$10^9$$. A guitar string has Q of $$10^3$$.

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