(10 Marks) Physics question (2)

In phase can be understood by the phase difference between two waves.
If the phase difference of two waves is 0 at a specific moment, then, the two wave is in phase at that moment.
The condition for 2 waves be in phase all the time is that, they have the same wavelenght and phase difference is 0.

In phrase means the two waves are constructive interference.
for example, trouph and trouph, crest and crest