If two waves of same frequency and same amplitude respectively, on superposition produce a resultant disturbance of the same amplitude, the waves differ in phase by

Resultant amplitude fl is given by=a12+a22+2a1a2cos⁡θ1/2 =a2+a2+2a2cos⁡θ1/2  But R=a ∴ a=2a2(1+cos⁡θ)1/2 =4a2cos2⁡θ/21/2 a=2acos⁡θ/2  or  cos⁡(θ/2)=1/2 or θ2=π3  or  θ=2π3