Question

Two waves having intensity I and 9I produce interference . If the resultant intensity at a point is 7 I, what is the phase difference between the two waves ?

Answer 1

Answer:

120' is the phase df between 2 wave$\begin{array}{l} 7{ I_{ o } }={ I_{ o } }+a{ I_{ o } }+2\sqrt { { I_{ o } } } \sqrt { x{ I_{ o } } } \cos \Delta \phi \\ \Rightarrow 7{ I_{ o } }=10{ I_{ o } }+6\cos \Delta \phi \\ \Rightarrow -3{ I_{ o } }=6\cos \Delta \phi \\ \cos \Delta \phi ={ { -1 } }{ 2 } \\ \Delta \phi =\dfrac { { 2\pi } }{ 3 } =\dfrac { { 2\times 180 } }{ 3 } ={ 120^{ 0 } } \\ Hence, \\ option\, \, C\, \, is\, \, correct\, \, answer. \end{array}$$