For effective cancellation, the delay in generating anti-noise must be:

  1. very small compared with the period of the noise
  2. exactly one second
  3. unimportant
  4. much longer than the period
Answer

A) very small compared with the period of the noise

Otherwise the phase will be wrong. SLO P-11-D-09 · Understanding

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