Beats are heard only if the two frequencies differ by:

  1. a very large amount
  2. zero
  3. a small amount (less than about 10–15 Hz)
  4. exactly double
Answer

C) a small amount (less than about 10–15 Hz)

Otherwise the ear hears two separate notes. SLO P-11-D-15 · Understanding

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