Question

The solar device used in traffic signal light, works on which of the following principles?
A. Conservation of momentum
B. Doppler effect
C. Photovoltaic effect
D. Electromagnetic induction

Answer 1

Hint: It is the phenomenon in which the voltage or current is produced when the device is subjected under the sun. When light is absorbed, it causes the excitation of the electrons and these free electrons are responsible for conduction of current.

Complete answer:
In the given question, we are given the solar device which is used in traffic signals. There is always a principle lying in a phenomenon, which explains the operation.Here, in this case, we are required to find the principle upon which the solar device used in the traffic signal light works.

To begin with, let us discuss a bit about the solar device. These are the devices which operate on solar energy. Solar energy is converted into electrical energy and fed to the system, which runs the device. This type of energy is getting much popularity as these do not need much installation costs and the generating cost is also very low. There are a number of appliances which nowadays run on solar energy. It is a termed as green energy as its installation does not make an impact on the trees, plants, etc.

There are four main types of solar energy.
1) Photovoltaic systems: Photovoltaic systems or, as they are also called, solar cell systems, which generate electricity directly from sunlight, are one of the most common methods of using solar power.
2) Solar water heating systems: A second form of solar energy is solar hot water, which means heating up water using the heat of the sun, as the name implies.
3) Solar power plants: Solar electricity is a third way we can tap the power of the sun for energy; it is typically used in industrial applications.
4) Passive solar heating

Photovoltaic effect: On exposure to light, the photovoltaic effect is the generation of voltage and electric current in a substrate. It is a process that is physical and chemical. There is a similar relationship between the photovoltaic effect and the photoelectric effect. Light is absorbed in any case, inducing excitation to a higher-energy state by an electron or other charge carrier.

The operation of the traffic signal lights is purely based on the photovoltaic effect. The correct option is C.

Note: While answering this question most of the students tend to make mistakes by choosing the principle as the electromagnetic induction. They fail to realise that to support electromagnetic induction, there a magnet should be present which induces current. However, in this case solar energy is directly converted into electrical energy.