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Interference and Energy Density
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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Update: June 2012
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