# Question Video: Identifying the Nature of the Interference between Two Waves Interfering Physics • 9th Grade

Two waves with the same frequency have a phase difference of 360°. Which of the following is the interference produced by the waves? [A] Constructive interference [B] Destructive interference [C] Neither constructive nor destructive interference

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### Video Transcript

Two waves with the same frequency have a phase difference of 360 degrees. Which of the following is the interference produced by the waves? (A) Constructive interference, (B) destructive interference, (C) neither constructive nor destructive interference.

Here, this problem tells us there are two waves with the same frequencies with a phase difference of 360 degrees. We are asked to figure out what kind of interference is produced by the waves when they interact with each other. In order to solve this problem, we should refresh our memories on how waves interact with each other in space. When two waves are occupying the same space at the same time, they will interfere with each other. If they have the same frequency, they will have a constant phase difference as they travel.

We are told that the two waves do have the same frequency in this problem, so they will have a constant phase difference throughout their interaction. There are two types of interference that can occur: constructive interference or destructive interference. Constructive interference happens when the interfering waves have a phase difference of zero. Notice how the highs and lows of the two waves match up. This means the resulting wave will have an amplitude equal to the sum of the amplitude of the two waves.

On the other hand, when the waves have a phase difference of 180 degrees, so that the peaks of one wave line up with the troughs of the other, they will interfere destructively. Notice how the highs and lows of these waves are opposite of each other. This will cause the equal amplitudes of the waves to cancel each other out like we see here, and the resulting wave will have an amplitude of zero. We′ve seen that the phase difference of waves that interfere destructively is 180 degrees. The phase difference of constructively interfering waves is zero degrees, which is the same as a phase difference of 360 degrees.

We are told that the waves in this example have a phase difference of 360 degrees. Therefore, there will be constructive interference between these two waves when they meet in space. So, the first option, constructive interference, is the correct answer.