In the Young's double slit experiment,if the phase difference between the two waves interfering at a point is $\phi$,the intensity at that point can be expressed by the expression:

• A
  $I = \sqrt{A^2 + B^2 \cos^2 \phi}$
• B
  $I = \frac{A}{B} \cos \phi$
• C
  $I = A + B \cos \frac{\phi}{2}$
• D
  $I = A + B \cos \phi$,where $A$ and $B$ depend upon the amplitudes of the two waves.