Intensity Questions

A point source emits sound equally in all directions in a non-absorbing medium. Two points P and Q are at distance of 2m and 3m respectively from the source. The ratio of the intensities of the waves at P and Q is :

Two periodic waves of intensities $I_1$ and $I_2$ pass through a region at the same time in the same direction. The sum of the maximum and minimum intensities is:

The number of photo electrons emitted for light of a frequency $\nu$ (higher than the threshold frequency ${\nu }_0$) is proportional to:

A lens having focal length $f$ and aperture of diameter $d$ forms an image of intensity $I$. Aperture of diameter $d/2$ in central region of lens is covered by a black paper. Focal length of lens and intensity of image now will be respectively:

Two sources of sound placed close to each other, are emitting progressive waves given by $y_1=4\sin 600\pi t$ and $y_2=5\sin 608\pi t$. An observer located near these two sources of sound will hear: