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


Question:
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?


Replies:
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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