According to the modern theory concerning atoms, electrons move in orbits around the nucleus.If an electron absorbs energy it is promoted to a higher energy orbit.
The wavelength of light λ (in meters), is related to the frequency v (in HZ) and to the speed of light c, by the equation:
λ = c/v
where c is the speed of light with a constant value of 300 million meters per second, is the frequency of the light in hertz (Hz) or cycles per second, and is the wavelength of the light in meters. From this relationship it is clear that the wavelength of light in inversely proportional to the frequency. An increase in frequency produces a proportional decrease in the wavelength of light with a corresponding increase in the energy of the photons that make up the light. Upon entering a new medium (such as glass or water), the speed and wavelength of light is reduced, although the frequency remains unaltered.
Explore how an electron absorbs energy, is excited into a higher energy state, and then decays at the Laboratory of Light
The relationship between the energy of a photon and it's frequency is dictated by another simple equation:
E = hv = hc/λ
where E is the energy in kiloJoules per mole, h is Planck's constant with a value of 6.626 x 10-34 Joule-seconds per particle, and the other variables were defined above.
Next figure illustrates the propagation of an electromagnetic wave in a direction from upper left to lower right. This wave travels at the speed of light and is known as a transverse wave where the direction of wave energy lies at right angles to the direction of propagation.
In this example, the wave is generating both electric and magnetic oscillating fields that are oriented at 90 degree angles with respect to each other and also to the direction of energy. The distance between two successive peaks in the illustration equals the wavelength of the radiation. The number of oscillations (equal to a single sinusoidal) per second equals the frequency of the radiation, which is usually measured in hertz (cycles per second).
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i.e., Planck's constant times the frequency, which is the energy of the photon, is sufficient to overcome the work function of the material, and the liberated electrons move under the influence of an applied electric field. From: Modern Dictionary of Electronics (Seventh Edition), 1999
Photon energy is the energy carried by a single photon. The amount of energy is directly proportional to the photon's electromagnetic frequency and thus, equivalently, is inversely proportional to the wavelength. The higher the photon's frequency, the higher its energy. Equivalently, the longer the photon's wavelength, the lower its energy.
Photon energy can be expressed using any unit of energy. Among the units commonly used to denote photon energy are the electronvolt (eV) and the joule (as well as its multiples, such as the microjoule). As one joule equals 6.24 × 1018 eV, the larger units may be more useful in denoting the energy of photons with higher frequency and higher energy, such as gamma rays, as opposed to lower energy photons, such as those in the radio frequency region of the electromagnetic spectrum.
Photon energy is directly proportional to frequency.[1]
E
=
h
f
{\displaystyle E=hf}
- E {\displaystyle E} is energy
- h {\displaystyle h} is the Planck constant
- f {\displaystyle f} is frequency
This equation is known as the Planck–Einstein relation.
Additionally,
E = h c λ {\displaystyle E={\frac {hc}{\lambda }}}
where- E is photon energy
- λ is the photon's wavelength
- c is the speed of light in vacuum
- h is the Planck constant
The photon energy at 1 Hz is equal to 6.62607015 × 10−34 J
That is equal to 4.135667697 × 10−15 eV
Electronvolt
Energy is often measured in electronvolts.
To find the photon energy in electronvolts using the wavelength in micrometres, the equation is approximately
E (eV) = 1.2398 λ (μm) {\displaystyle E{\text{ (eV)}}={\frac {1.2398}{\lambda {\text{ (μm)}}}}}This equation only holds if the wavelength is measured in micrometers.
The photon energy at 1 μm wavelength, the wavelength of near infrared radiation, is approximately 1.2398 eV.
In chemistry, quantum physics and optical engineering
See [2]
E = h ν {\displaystyle E=h{\nu }}
where- E is photon energy (joules),
- h is the Planck constant
- The Greek letter ν (nu) is the photon's frequency.
An FM radio station transmitting at 100 MHz emits photons with an energy of about 4.1357 × 10−7 eV. This minuscule amount of energy is approximately 8 × 10−13 times the electron's mass (via mass-energy equivalence).
Very-high-energy gamma rays have photon energies of 100 GeV to over 1 PeV (1011 to 1015 electronvolts) or 16 nanojoules to 160 microjoules.[3] This corresponds to frequencies of 2.42 × 1025 to 2.42 × 1029 Hz.
During photosynthesis, specific chlorophyll molecules absorb red-light photons at a wavelength of 700 nm in the photosystem I, corresponding to an energy of each photon of ≈ 2 eV ≈ 3 × 10−19 J ≈ 75 kBT, where kBT denotes the thermal energy. A minimum of 48 photons is needed for the synthesis of a single glucose molecule from CO2 and water (chemical potential difference 5 × 10−18 J) with a maximal energy conversion efficiency of 35%.
- Photon
- Electromagnetic radiation
- Electromagnetic spectrum
- Planck constant
- Planck–Einstein relation
- Soft photon
- ^ "Energy of Photon". Photovoltaic Education Network, pveducation.org. Archived from the original on 2016-07-12. Retrieved 2015-06-21.
- ^ Andrew Liddle (27 April 2015). An Introduction to Modern Cosmology. John Wiley & Sons. p. 16. ISBN 978-1-118-69025-3.
- ^ Sciences, Chinese Academy of. "Observatory discovers a dozen PeVatrons and photons exceeding 1 PeV, launches ultra-high-energy gamma astronomy era". phys.org. Retrieved 2021-11-25.
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