# Homework Help: Amplitude of resultant waves

1. Sep 15, 2014

### somecelxis

1. The problem statement, all variables and given/known data

The energy transferred per second by a progressive waves is directly proportional to the square of amplitude . If two different amplitude waves superpose , the energy per second transferred by the resulatant waves us direcly proportional to (ANS: the diffrence of amplitude)

why the ans shouldnt be sum of amplitude?

2. Relevant equations

3. The attempt at a solution
in my opinion , when 2 waves superposed , the resultant intensity is I1 +I2 ....but intensity is directly proportional to amplitude square , so the resultant amplitude should be sqrt root of ( (I1)^2 + (I1)^2 )

2. Sep 15, 2014

### cwasdqwe

Superposition principle isn't valid for power (energy per second transferred), for it is not a linear operation.

3. Sep 15, 2014

### rude man

Second, the energy transferred per unit time depends on the phasing of the two waves.

Third, if the phase happens to be zero the intensity is proportional to the square of the sum of the two amplitudes.

4. Sep 15, 2014

### cwasdqwe

Of course it dependes on phase, and let's assume they are in phase with the purpose of understanding his question, and not adding more questions to the initial problem. Your third claim doesn't contradict my answer, though...

5. Sep 15, 2014

### rude man

I was addressing the OP, not you. Should have made that clearer.

6. Sep 15, 2014

### cwasdqwe

It's ok, I did misunderstand it too. My excuses.

7. Sep 16, 2014

### somecelxis

so the ans should be intensity is proportional to the square of the sum of the two amplitudes
?

8. Sep 16, 2014

### rude man

Yes, if they're in phase.