# Homework Help: Superposition of waves

1. Jun 28, 2014

### desmond iking

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

when a point is intefered by 2 waves of different phase , the resultant is y1 + y2 .... but why the resultant amplitude cant be = A1 + A2 ... but is sqrt root ((A1)^2 + (A2)^2) ??

this is actually a online note.

2. Relevant equations

3. The attempt at a solution

#### Attached Files:

• ###### ll'.png
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2. Jun 28, 2014

### Staff: Mentor

It isn't, and your pic shows it isn't. The peak of the resultant amplitude is determined using the cosine rule and the phase angle difference. Only if the phase angle was 90 degrees would your equation using Pythagoras hold.

3. Jun 29, 2014

### desmond iking

sorry, i mean why cant i add up A1 and A2 to get the resultant amplitude... tHat means resultant amplitude =A1+ A2

4. Jun 29, 2014

### dauto

Because y1 and y2 never reach their maximum values at the same time. unless they're in phase (θ = 0).