The displacements of two interfering light waves are y1=4  sinωt and y2=3  cos(ωt) . The amplitude of the resultant wave is (y1  and y2  are in CGS system)

The given values are A1=4cm,  A2=3cm,   ϕ=π2 Resultant amplitude A=A12+A22+2A1A2cosϕ                                            =42+32+2×4×3 cos (π2)                                            =16+9+24 cos 900                                            =16+9+24 (0)                                            =25                                             =5 cm