Diffraction and interference of light suggest

Two light sources have amplitudes $a$ and $2a$ respectively. If they interfere with a phase difference of $\pi$,what is the resultant minimum intensity?

When a light wave goes from air into water,the quality that remains unchanged is its

Two coherent monochromatic light beams of intensities $I$ and $4I$ are superposed. The maximum and minimum possible intensities in the resulting beam are

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

Two coherent sources of intensities,$I_1$ and $I_2$ produce an interference pattern. The maximum intensity in the interference pattern will be