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Photon energy is defined as the energy carried by a single photon.
- The amount of energy is directly proportional to the electromagnetic frequency of the photon.
- It is inversely proportional to the wavelength of the photon.
- The higher the frequency of the photon, the greater its energy.
- Similarly, the energy of the photon decreases as its wavelength increases.
- Photon energy can be quantified using any unit of energy.
- The electronvolt (eV) and the joule are two commonly used units that denote photon energy.
- One joule is equal to 6.24 × 1018 eV.
| Table of Content |
Key Terms: Photon energy, Frequency, Wavelength, Quanta, Light, Energy, Kinetic energy, Planck’s constant, Electronvolt, Joule, Binding energy
What is Photon Energy?
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Photon energy is defined as the energy of a quantum of light.
- Light has the dual nature of being both a wave and a particle.
- The particle of light is referred to as a quanta or photon of light.
- The energy carried by photons of light is referred to as photon energy.
- The photon is defined by either its wavelength or its frequency.
- Different lights possess different frequencies, as do their photons.
- Photons with higher frequencies contain more energy than photons with lower frequencies.
Photon Energy
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| Charge to Mass Ratio of Electron | Activation Energy Formula | Degree of Unsaturation Formula |
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Properties of Photon
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The following are the properties of photons
- Photons have no electrical charge.
- The velocity of photons is equivalent to the speed of light.
- Photons have no mass, but their energy is E = hf = hc/ λ.
- The photon energy is inversely proportional to the electromagnetic wave's wavelength.
- The photon is more energetic when its wavelength is shorter, and less energetic when its wavelength is longer.
- Photons can be generated and destroyed with minimal loss of energy or momentum.
- When EM waves are emitted by a source, photons are emitted.
- When they come into contact with matter, they can be absorbed and their energy transferred.
- Photon always travels in a straight line.
Photon Energy Formula
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The formula of photon energy can be expressed in the way given below:
E = hf
Where
- E is the energy of a photon
- h is Planck’s constant
- f is the frequency of the photon
In addition, the frequency of the photon is c/ λ, therefore
E = hc/λ
Where
- λ is the wavelength of a photon.
- c is the speed of light in a vacuum
We observe from the energy of photon equation that the energy of a photon depends on the following parameters:
- The energy of a photon is directly proportional to the electromagnetic frequency of the photon.
- The energy of the photon is inversely proportional to the wavelength.
- The higher the photon energy frequency, the more its energy.
- However, on the other hand, the longer the photon’s wavelength, the lower its energy.
Photon Energy in Electronvolts
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Energy is often measured in electron volts. The equation for calculating photon energy in electronvolts based on wavelength in micrometers is approximately
\(E(eV)=\frac {1.2398}{\lambda (\mu m) }\)
The above equation holds only when the wavelength is measured in micrometers. The photon energy at 1 μm, the wavelength of near-infrared light, is about 1.2398 eV.
Kinetic Energy of Photon Formula
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The photoelectric effect demonstrates that electrons are strongly bonded to the metal surface. In the photoemission process, electrons emitted have some energy. The formula gives the maximum kinetic energy of emitted electrons.
KEe = hf - BE
Where
- hf = E is the photon energy
- BE = binding energy/ the Work function of the electron, that is particular to the given material.
- KEe = kinetic energy (in Joules)
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Things to Remember
- Photon energy is defined as the energy of a quantum of light.
- The energy carried by photons of light is referred to as photon energy.
- Photons with higher frequencies contain more energy than photons with lower frequencies.
- The energy of a photon is given by E = hf.
- In terms of wavelength, photon energy is given by E = hc/λ.
- The kinetic energy of a photon is given by KEe = hf - BE.
Sample Questions
Ques. What is photon energy? (2 Marks)
Ans. Photon energy is defined as the energy carried by a single photon. The amount of energy is related to the photon's electromagnetic frequency, and consequently inversely proportional to its wavelength. The higher the photon's frequency, the greater its energy.
Ques. What is the relation between photon energy and electromagnetic frequency? (1 Mark)
Ans. The energy of a photon is directly proportional to the photon's electromagnetic frequency.
Ques. What is the relationship between joule and electronvolt? (1 Mark)
Ans. 1 Joule is given by
1 Joule = 6.24 × 1018 eV
Ques. What purpose does photon energy serve? (2 Marks)
Ans. Although photon energy (light energy as quantum energy) is more valuable than heat energy, most solar beams tend to convert to ambient heat. Solar beams' most efficient work will be done by using their quantum characteristics, just as plants' photosynthetic processes do.
Ques. What is the mechanism by which a photon transports energy? (2 Marks)
Ans. Despite its lack of bulk, light does carry energy via its motion. Because photons (light particles) have no mass, they must obey E = pc and derive their whole energy from their momentum. In the general equation, there is now an interesting additional impact.
Ques. Is a photon a particle or a wave? (2 Marks)
Ans. Light is a particle (photon), and the passage of photons is a wave, according to Einstein. Einstein's light quantum theory's fundamental premise is that light's energy is proportional to its oscillation frequency.
Ques. Is it true that photons have spin? (2 Marks)
Ans. Electrons and quarks (matter particles) can have spins of –1/2 or +1/2; photons (light particles) can have spins of –1 or +1, and Higgs bosons must have spins of 0. Particle spins, despite their small size, have a significant impact on our daily lives. We can make 3D movies thanks to photons' spin characteristics.
Ques. A sodium lamp emits yellow light with a frequency of 5.10 x 1014 Hz. How much energy is contained in 1.5 mol of photons? h=6.63∗10−34 J⋅s. (3 Marks)
Ans. The energy of a single photon is given by the equation:
E = hf
We are given the frequency and the value of the constant, allowing us to solve.
E= (6.63 x 10−34 J⋅s) (5.10 x 1014 Hz) =3.38 x 10−19 J
The above gives the energy contained in one photon. Next, solve for the energy contained in 1.5mol using Avogadro's number:
(1.5mol x 6.022 x 1023photons/1mol) x (3.38 x 10−19J/1photon) = 3.1 x 105J
Ques. What happens when a photon is created? (2 Marks)
Ans. When an electron in a higher-than-normal orbit returns to its normal orbit, a photon is produced. During the transition from high to low energy, the electron emits a photon, which is a packet of energy with highly precise properties. Photons are generated when sodium atoms are energized by a sodium vapor light.
Ques. If the energy of a photon is 350 × 10−10 J, determine the wavelength of that photon. (3 Marks)
Ans. Given parameters are,
E = 350×10−10J
c = 3×108m/s
h = 6.626×10−34Js
The Photon energy formula is given by,
E = hc / λ
λ = hc / E
λ = 6.626×10−34×3×108 / 350×10−10
λ = 19.87 x 10-28 / 350 x 10−10
λ = 0.056 x 10-16 m
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