1) Two identical light waves having phase difference 'ϕ' propagate in same direction, when they superpose , the intensity of resultant wave is proportional to A) cos2ϕ B) cos2ϕ2 C) cos2ϕ3 D) cos2ϕ4 Answer: Option BExplanation:For two coherent sources , the resultant intensity is given as, lR=l1+l2+2√l1l2cosϕ ∴ Fror two identical light waves, l1=l2=l ⇒ lR=4lcos2ϕ2 ∴ lR∝cos2ϕ2