Energy Talk!

kemunkhimhun asked:


Energy is proportional the square of amplitude but in interference the resultant amplitude is 2 times the original amplitude implies energy becomes 4 times of initial wave energy.It violets energy conservation.
How it actually happens?

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One Response to “Energy conservation in interference of light?”

1. Somu Says:
   December 10th, 2007 at 4:27 am

   Let E1 = amplitude of first wave,
   E2 = amplitude of second wave
   Then total energy before inteference = 1/2 E1^2 + 1/2 E2^2
   = 1/2 (E1^2 + E2^2)
   Total energy after interference = 1/2 (E1+E2)^2
   = 1/2 (E1^2 + E2^2 + 2E1E2)
   1/2 (E1^2 + E2^2) + E1E2
   So E1E2 is extra. This is what you are talking. Right?

   Here is the explanation.
   E1 and E2 are vectors. So, in place of E1E2 you should take
   E1.E2 which means dot product of E1 and E2. There are constructive and destructive interferences. When the waves meet, then in some places the dot product is positive and other places negative so that when you add all of them, then total value of the dot product becomes zero.
   Thus energy is conserved.