Question

Assertion: In the street light circuits, photo-cells are used to switch on and off the lights automatically at dusk and dawn.
Reason: A photocell can convert a change in intensity of illumination into a change in photocurrent that can be used to control lightning systems.
A. Both the assertion and the reason are correct and reason is the correct explanation for the assertion
B. Both the assertion and the reason are correct and reason is not the correct explanation for the assertion
C. Assertion is correct but reason is incorrect
D. Both assertion and reason are incorrect

Answer 1

A solid-state device that by generating a voltage, transforms light into electrical energy, as in a photovoltaic cell, or uses light to regulate current flow, as in a photoconductive cell: used in automatic door control systems, illumination, etc.

Complete answer:
In the given question, we are talking about the photocells and their operation in the street lights. We must have wondered that the streetlights are automatically switched on during the dusk and automatically switched on at dawn. There is a certain mechanism inside the street lights which contains photocells.

Let us discuss photocells in order to understand in a better way. Electronic instruments that can be used to control indoor or outdoor lighting are photocells and motion sensors. These sensors boost your home's protection and protection, automatically switch on lights when it gets dark or motion is sensed. When excess light is unnecessary, they often conserve electricity by shutting themselves off. A photocell is a resistor that, based on the amount of light impacting on it, alters resistance. Semiconductor photoconductivity is operated by a photocell: the energy of photons entering the semiconductor frees electrons to flow, minimising resistance.

So, these are installed inside the street lights, which need to power on the street lights according to the weather. Such an efficient way of operation can drastically reduce the accidents on the road, which often takes place due to combination of bad weather and low light, which reduces the visibility of vehicles on the road. So, it is absolutely correct that a photocell can convert a change in intensity of illumination into a change in photocurrent that can be used to control lightning systems.

Hence, both the assertion and the reason are correct and reason is the correct explanation for the assertion.The correct option is A.

Note: Photocells are electronic devices and these can go bad too. If the light glows continuously, then we can be sure that the photocell is no longer active in it and it should be replaced. It is important to note that a special type of metal is used in the photocells, which is Caesium.