Two coherent sources can have:

  1. a constant non-zero phase difference
  2. different frequencies
  3. only zero phase difference
  4. a random phase difference
Answer

A) a constant non-zero phase difference

Phase difference must be constant, not necessarily zero. SLO P-11-D-14 · Understanding

Physics MCQ · More Superposition, Stationary Waves and Beats MCQs · Practise