Particle Nature of Light Explanation and Duality
Max Planck, a renowned German scientist, found in 1900 that particular types of metals ejected free electrons in contact with light. This experiment duly dealt with the photoelectric effect. Later on, Albert Einstein followed up on this experiment and discovered the particle nature of light. He stated that the electromagnetic energy comes in packets or quanta, also termed 'photons'.
According to the former observations, the wavelength of light had a massive influence on the ejected electrons. Also, the intensity of light directly impacts the electrons thus released. This fact pointed to the particle nature of light, which scientists previously considered a wave.
What is Particle Nature of Light?
Until 1900, physicists assumed that light travelled in the form of waves. However, the photoelectric effect experiment suggested that it also possesses energy packets. Even other forms of electromagnetic energy comprise quanta of energy.
What we call 'photons' today are nothing but constituents of energy. Photons are energy-containing packets.
Some of the examples of photons are
When the sun converts particles both into heat and light, it's in the form of photons.
A carrier of an electromagnetic force.
In turn, it helped them arrive at the particle nature of light.
Moreover, scientists such as Albert Einstein observed a few highlights mentioned below.
- Light sources with longer wavelengths contain lesser energy. This mainly refers to red and orange.
- Contrarily, shorter wavelengths contain higher photons or packets of energy.
- Consequently, wavelengths with higher energy content displaced a more significant number of free electrons from metal surfaces.
This last observation helped Planck find out that the frequency of a light source was directly proportional to the radiation of such electrons.
What is Wave-Particle Duality?
As you know now, light contains photons or quanta of energy that assigns particle nature to it. Yet, it also comes in the form of waves, as the English scientist Thomas Young concluded through his Interference experiment.
Young's Double-Slit Experiment
In Young's double-slit experiment, electrons were struck on the double-slit, resulting in definitive proof of the wave character of light.
In conclusion, Young's double-slit experiment supported the 'duality nature of light'.
Therefore, you can recall the famous adage that "light is not only a wave but also a particle". It refers to wave-particle duality as it is known today. Consequently, a photon possesses both the characteristics of a particle and a wave. Scientists of that time arrived at this conclusion after conducting a series of quantum-mechanical experiments.
As a result, the particle nature of light comes into play when it interacts with metals and irradiates free electrons. Contrarily, wave nature is prominent when seen in the field of propagation of light. Besides, photons assume an essential role in the electromagnetic propagation of energy.
Thus, light exhibits a wave-particle duality.
De-Broglie’s Dual Nature of Matter
According to de Broglie’s dual nature of matter, it exhibits wave properties such as diffraction and interference when the matter is moving. Whereas when the matter is at rest, it exhibits particle properties. Therefore, de Broglie’s wavelength supported the fact that 'matter has dual nature', and so does light.
The relation between wave and particle properties is also given by 'the de Broglie’s relation.'
According to de Broglie’s relation, light exhibits 'wavelike' and 'particle-like' properties.
E= hv , p= hc/(λ)
here, c = velocity of light
v = frequency
h = Planck constant = 6.627× 1027
E = energy
λ = de-Broglie wavelength of light
Hence, the de Broglie's relation
Now that you know the relation between the photoelectric effect and the nature of light, it is time to discuss some of the properties of photons.
These are some more basic concepts and theories related to the 'wave-particle duality.
Heisenberg's uncertainty principle
quantum field theory
The concept of wave-particle duality is an ongoing vexed question in modern physics.
What are the Characteristics of Photons?
Some of the most prominent characteristics of photons include the following -
Photons are theoretically the smallest quantum of electromagnetic energy or radiation. Therefore, it forms the essential constituent of light.
The letter 'c' denotes it in mathematical expressions. Also, it possesses a speed of 2.99 X 108 m s¹. Besides, it is never restive, meaning that it is always in motion. On the other hand, photons travel only in a vacuum at this speed.
The energy of a photon is equivalent to the product of the oscillation frequency of the light source and Planck's constant. Therefore, E=hv, where 'v' refers to frequency. 'h' in this equation implies Planck's constant, which is 6.62607004 X 10-34 m2kg/s. You can also express it as E = hv hc/nλ, where A stands for = wavelength.
However, the formula for a photon's momentum is p = hv/c.
It is stable and lacks an electric charge.
When a photon interacts with other subatomic particles like electrons, the successive phenomenon is referred to as the Compton effect. Besides, such a collision duly conserves total energy and momentum. Therefore, you can refer to it as an elastic collision, preserving overall energy and momentum.
It is also theoretically massless. However, these quantum packets transfer energy only after collisions with other particles.
When an empty space, photons can travel at the speed of light.
Some More Facts About Photons
Not only light but all the electromagnetic energy such as microwaves, radio waves, X-rays are made up of photons.
Gilbert N. Lewis first used the word 'photon' to describe it, but actually, the concept of the photon was first used by Albert Einstein.
Photons do not decay on their own.
The overall charge on the photon is always '0', i.e., it is always 'electrically neutral'.
Therefore, the answer to the question of which phenomenon shows the particle nature of light is the photoelectric effect.
Photoelectric Effect
In this phenomenon, when electromagnetic radiation (such as light) hits the material, the emission of electrons takes place. It was first discovered by Heinrich Hertz in 1887.
In the photoelectric effect, if the frequency is too low, no electron is seen getting freed. But, if the frequency is high enough, some electrons can be observed.
These observations prove that.
Light is made of particles.
The energy of the particle increases with the frequency
Each particle gives its energy to just one electron.
FAQs on Particle Nature of Light
1. What is Light, What is its Nature?
Light implies a range of electromagnetic waves which the human eye can perceive. It can also be described as the massless packets of energy that travel in the form of waves with light speed. It has both wave and particle nature. The experiments on diffraction and interference helped illustrate the wave nature of light. Like all the other electromagnetic waves, light can travel through a vacuum. Light can travel as a 'wave' or a 'photon'.
2. Name a Phenomenon Which illustrates the Particle Nature of Light? Give reason for the following?
Photoelectric effect illustrates the particle nature of light. In the photoelectric effect, If we shine a light on metal with energy below the binding energy of an electron, no electrons from the metal will be ejected. But, if the frequency of light is high enough such that the energy exceeds the binding energy, the electrons from the metal are knocked off the metal. Therefore, the energy will be conserved, and 'conservation of energy in a collision is particle-like behaviour. Thus, the photoelectric effect explains light's particle behaviour.
3. Is Light a Particle or a Wave?
Light has a dual nature, which suggests that it comprises both wave and particle. Einstein believed that light is a particle (photon) but according to Quantum mechanics, we came to know that light can act simultaneously as a particle or a wave. Light mainly behaves as a wave, but due to the 'photons' or the 'tiny packages of energy, light is also considered to be a particle in nature. Hence, studies have shown the dual nature of light, which varies with the amount of energy and frequency of light.
4. How does the Heisenberg Uncertainty Principle relate to wave-particle duality?
According to wave-particle duality, it states that every particle or quantum can be classified as either a particle or a wave. On the other hand, the uncertainty principle is the idea that specific pairs of things about a quantum particle are impossible to be known at once. Hence, the Uncertainty Principle is a statement of the effect of wave-particle duality on the properties of subatomic objects.
5. Differentiate between particle and wave nature of light.
Particle nature of light | Wave nature of light |
Particle nature of light states that light consists of particles called 'Photons'. | Wave nature of light states that light behaves as an electromagnetic wave. |
Particles do not interfere. That is, when the space is occupied by some particle, other particles cannot occupy the same space. | Waves can interfere. That is, a number of waves can exist in the same space simultaneously. |
When a number of particles are present in a space, its total value is equal to its sum. | When a number of waves are present in the same space, the resultant wave can be 'smaller' or 'larger' in magnitude and will be directed to the side where the majority of waves are pointing. This is due to the phenomenon of 'interference'. |