Two identical light waves, A and B, are emitted from different sources and meet at point P. The distance from the source of A to point P is LA. The distance from the source of B to point P is LB. Which of the following statements is necessarily true concerning the interference of the two waves?
  1. A and B will interfere constructively because their amplitudes are the same.
  2. A and B will interfere constructively if LA= LB
  3. A and B will interfere destructively if LA-LB=mλ where m=0,1,2,3,...
  4. A and B will interfere destructively if LA is not equal to LB
  5. A and B will interfere constructively because their wavelengths are the same.