In Young's double slit experiment, one of the slit is wider than other, so that the amplitude of the light from one slit is double of that from other slit. If $$I_m$$ be the maximum intensity, the resultant intensity $$I$$ when they interfere at phase difference $$\phi$$ is given by

A

$$\frac{I_m}{9}(4 + 5\cos\phi)$$

B

$$\frac{I_m}{3}\left(1 + 2\cos^2\frac{\phi}{2}\right)$$

C

$$\frac{I_m}{5}\left(1 + 4\cos^2\frac{\phi}{2}\right)$$

D

$$\frac{I_m}{9}\left(1 + 8\cos^2\frac{\phi}{2}\right)$$