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### Constructive and Destructive Interference

Posted: Thu Oct 10, 2019 8:26 pm
I just finished the module explaining the wave properties of electrons. I need some clarification on constructive interference and destructive interference. How does each type interference affect the outcome of the diffraction pattern? Does the energy of the resulting wave have a correlation with the diffraction pattern?

### Re: Constructive and Destructive Interference

Posted: Thu Oct 10, 2019 8:38 pm
Hello!

Constructive interference occurs when two different waves are acting IN phase and the result is more energy.
Destructive interference occurs when two different waves are acting OUT OF phase and the result is less energy.

Waves are in phase when their troughs and peaks match up and they are out if phase when they don't match up.

So how I like to think of it in terms of a sine graph.

So, for 2 waves IN PHASE I think of 2 sine waves where they start at the same point x=0.
for 2 waves OUT OF PHASE I think of 2 sine waves where one starts at x=0 and another starts at x= pi/2.

I hope this helps.

### Re: Constructive and Destructive Interference

Posted: Fri Oct 11, 2019 10:49 am
Yes, you can see the effect of the interference in the diffraction pattern, and depending on how in-phase/out of phase the waves are, you will see different patterns. If you have two waves undergoing constructive interference, the amplitude of the resulting wave gets larger, so the light will be brighter/more intense. Destructive interference will result in a lower amplitude of the resulting wave, so the light is less bright/intense.

### Re: Constructive and Destructive Interference

Posted: Fri Oct 11, 2019 6:05 pm
why does destructive interference/waves that are out of phase sometimes cause there to be no wave at all?

### Re: Constructive and Destructive Interference

Posted: Sat Oct 12, 2019 1:06 pm
Another way to think of constructive v destructive waves is that when two waves are in phase, meaning they are both peaks or both troughs at the same moment, you add them. These are constructive waves. Moreover, when two waves are out of phase, meaning one is a trough and the other is a peak at the same moment, you subtract them, thereby being an example of destructive interference.