Question

Which of the following are photocells?
(i) Photoemissive cells
(ii) Photovoltaic cell
(iii) Photoconductivity cell
(iv) Solar cell
A. (i), (ii)
B. (iii), (iv)
C. (ii), (iii) and (iv)
D. (i), (ii), (iii), (iv)

Answer 1

Photocells are the cells that convert light energy into electrical energy. They have a variety of types based on their mechanism but the main functions of all remain the same, i.e. converting light energy into electrical energy. They have a wide range of applications like solar panels, solar automobiles, etc.

Complete answer:
Photoemissive cells function by emitting electrons from their surface when the light of a particular wavelength falls on it, thus converting light energy into electrical energy.Photovoltaic cells consist of one or two layers of semiconductor material, usually silicon. When light hits the battery, it creates an electric field between the layers, allowing current to flow.

The photoconductive cell is a semiconductor device with two ends, and its terminal resistance changes with the intensity of incident light (linear). When sunlight hits the solar cell, electrons will be ejected from the silicon, forming "holes"-voids left by escaping electrons. If this happens in an electric field, the electric field will move electrons to the n-layer and holes to the p-layer.

Therefore, the correct answer is D.

Note: A photocell is a sensor that allows you to perceive light. The main features of photocells include small size, energy-saving, economical, and ease to use. For these reasons, they are widely used in gadgets, toys, and equipment. These sensors are commonly referred to as cadmium sulfide (CdS) batteries. They are composed of photoresistors and LDRs.