What is Photoemissive cell used for?

Consider the following statements regarding the photoelectric effect experiment:

(I) Photoelectrons are emitted as soon as the metal is exposed to light.

(II) There is a minimum frequency below which no photo-current is observed.

(III) The stopping potential is proportional to the frequency of light.

(IV) The photo-current varies linearly with the intensity of the light.

Which of the above statements indicate that light consists of quanta (photons) with energy proportional to frequency?

Explain the working of photo emissive cell. Write any two applications of photoelectric cells.

It is essential to consider light as a stream of photons to explain?

Which of the following is/are correct graph for photoelectric effect?

Represent the union of two sets by Venn diagram for each of the following.

$X=\{x | x$ is a prime number between $80$ and $100\}$

$Y=\{y | y$ is an odd number between $90$ and $100\}$

Describe the construction of a photoelectric cell.