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Name:  Eric D.
Status: educator
Age: 50s
Location: N/A
Country: N/A
Date: 2000-2001

I understand the effects of constructive & destructive interference relative to light waves (eg Young's double-slit). My question is, when two light waves of the same wavelength destructively interfere, where does the wave's energy go? Is the energy density at the point of interference zero?

Eric, When destructive interference of light waves occurs, the energy does not disappear. It is no longer distributed evenly. Light from a two-slit device forms a pattern with very bright and very dark parts. There is practically no energy at dark fringe, zero energy density. There is a great deal of energy at the bright fringe, a large energy density. The total energy over the entire pattern equals the energy from one slit plus the energy from the second slit. Interference re-directs the energy.

Dr. Ken Mellendorf
Illinois Central College

The waves' energies simply add together. In places where the interference is destructive, one wave cancels out the other. (up + down = nothing.) Where it is constructive, however, they reinforce each other (up + up = 2 * up, down + down = 2 * down.) That is all there is to it.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois

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