Which property of light made solar power possible?

You have installed the solar system at your rooftop and enjoying the smooth electricity.

Do you know that the light beam falling on the surface of the solar panels is actually made up of billions of billions small packets of energy known as Photons?

In this post, I will discuss that property of light which made solar power possible.

Before going ahead let me remind you that solar power is a source of clean energy which converts sunlight into electricity to run our electrical appliances.

Sunlight is an electromagnetic wave in which electric field and magnetic field are mutually perpendicular to each other and also to the wave propagation.

Dual nature of light

Earlier, the physicists assume that the light has the wave nature only as all the phenomenon like:

• Reflection (Throwing back or bouncing back of light from the surface)
• Refraction (Bending of light while traveling from one medium to another)
• Interference (Superposition of 2 or more waves to form a resultant wave)
• Diffraction (Bending of waves around obstacles or openings)
• Polarization (Describes the geometrical orientation of the transverse waves)

can be easily explained by assuming the wave nature of light.
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Until a new phenomenon happened, the photoelectric effect, which physicists found difficult to explain through the wave nature of light.

The Photoelectric effect is fully explained when we assume that the light has a particle nature.
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This forced the physicists to consider that the light also has particle properties on the quantum scale of the atom in addition to its wave nature.

Finally, it was concluded that light has dual nature; wave as well as a particle.

What is Photon?

The smallest discrete amount or quantum of the electromagnetic radiations is called as the Photon.  It is the basic unit of light, meaning that the light is made up of photons.
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The quantum is the smallest amount of anything and 1 quantum of electromagnetic radiation is called the Photon.

It’s concept arrived from the quantum mechanics which describes the behavior of the particle on atomic and sub-atomic levels.

I am highlighting some of their properties:

• They are always moving
• They have zero mass
• They are neutral
• They travel with the speed of light in space

The photon describes the particle property of the electromagnetic wave. In other words, the electromagnetic waves are made of individual particles called photons. 

The Photoelectric effect

It was the photoelectric effect that made physicists think that light behaves as the particle and this property of light made the solar power possible. The idea of photons originated from the property of the photoelectric effect.

The photoelectric effect occurs when the electrons are released after the light is incident on a metal. The electrons released are called photo-electrons.

This happens because the energy of photons is absorbed and transferred to the electrons of the metals. The electrons get excited and jump from valence band, crossing the band gap, to the conduction band.

The free electron in the conduction band constitutes the current.

Einstein explained this phenomenon by assuming that the energy from light comes in a discrete form called photons. The energy in each quantum or a bundle is equal to the frequency multiplied by the constant called Plank’s constant.

It can be written as:

• ​Energy = Plank’s constant (h) x Frequency of the photon (ʋ)

The Photoelectric effect

To observe the photoelectric effect the frequency of the falling photon must be higher than the frequency called the threshold frequency of the specific metal of the energy of the photon must be greater than the binding energy of the specific metal.

Notice in the above picture that the red light is not able to knock out the electrons from potassium metal as it’s energy (1.77 eV) is less than the minimum threshold energy (2 eV) to pluck the electrons. No photoelectric effect will be observed.

Whereas, the green light (2.25 eV) and the Violet light (3.1 eV) has higher energies than the minimum energy required by the metal.

Hence, the electrons will be ejected and the photoelectric effect will be observed. The excess energy available will be converted into Kinetic energy and the electrons will be set into motion, constituting the electric current.

This can be written in the equation form as follows:

• H ʋ = Binding Energy + Kinetic Energy

H= Plank’s constant (6.626176 x 10-34 joule-seconds)
ʋ = Frequency

The photons with energy collide with the electrons of the metal and in this collision, they transfer their energy to the electrons and set them into motion just like when a moving ball hits another ball at rest, setting it into motion.

The main condition is that the transferred energy of the photons must be higher than the binding energy of the metal, only then the electron will eject and will constitute a current otherwise no current is seen.

The whole phenomenon can be explained very easily when we consider light as a particle.

So, in the above case, the light energy is converted into electrical energy which made the basis of solar power. The solar panels use the photoelectric property of light to make this conversion.

Or in other words, the photoelectric property made solar power possible.

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