Interference and Energy Density
Name: Eric D.
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?
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.
PG Research Foundation, Darien, Illinois
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Update: June 2012