For a distinct interference pattern,the condition is that the ratio of intensities of light produced by both sources must be .....

Two light waves of intensity $I$ and $4I$ superpose at point $A$ with zero phase difference and at point $B$ with a phase difference of $\frac{\pi}{2}$. Calculate the difference of resultant intensities at point $A$ and $B$. (in $I$)

The phenomenon of interference is exhibited by:

If the wavelength of light is $4000 \text{ Å}$, then the number of waves in $1 \text{ mm}$ length will be . . . . . . -

Consider the following statements about interference of light.
$A$-When crest of one wave coincides with crest of another wave at a point,this point is a point of destructive interference.
$B$-Two coherent sources emit waves of the same frequency with a constant phase difference.
Choose the correct option from the following.

Two beams of light having intensities $I$ and $4I$ interfere to produce fringes on a screen. The phase difference between the beams at point $A$ is $\pi/2$ and at point $B$ is $2\pi$. Find the resultant intensities at points $A$ and $B$.