What Is Electronvolt?
An electronvolt is a very small unit used to measure energy. Scientists use it when they study tiny things like electrons, atoms and particles inside atoms. The symbol for electronvolt is eV.
One electronvolt is the amount of energy an electron gets when it is pushed by an electric force of one volt. It is much smaller than the joule, which is the common unit of energy in the International System of Units.
Definition
In simple words, an electronvolt is:
- Energy gained or lost by one single electron
- When it moves through an electric potential difference of one volt
In standard physics units, one electronvolt is equal to:
- 1 eV ≈ 1.602 176 634 × 10−19 joule
- This is about 0.00000000000000000016 joule
Because this number is so tiny, electronvolts are very useful for talking about the energy of electrons, photons, atoms and particles without always using long decimal numbers.
History / Origin
The idea of the electronvolt came from early studies of electricity and electrons in the late 19th and early 20th century.
Scientists already used the volt to talk about electric potential. They also knew that electrons carry a fixed electric charge. So they defined a new energy unit based on these two ideas:
- The charge of one electron
- Times a one volt potential difference
The name electronvolt comes from joining the words electron and volt. Over time, as atomic and nuclear physics grew, the electronvolt became a standard unit for very small energies. Today it is widely used in research labs, particle accelerators and space science, even though the official SI energy unit is the joule.
Symbol & Abbreviation
The main symbol for electronvolt is:
- eV for electronvolt
Because one eV is so small, scientists often use larger units made from it using prefixes:
- meV milli electronvolt, 1 meV = 0.001 eV
- keV kilo electronvolt, 1 keV = 1 000 eV
- MeV mega electronvolt, 1 MeV = 1 000 000 eV
- GeV giga electronvolt, 1 GeV = 1 000 000 000 eV
- TeV tera electronvolt, 1 TeV = 1 000 000 000 000 eV
These larger units make it easier to write and compare the energies of particles in experiments and in space.
Current Use Around the World
Electronvolts are used all over the world in many parts of physics. Some common areas include:
- Atomic physics to describe the energy levels of electrons in atoms
- Nuclear physics to measure binding energies inside the nucleus
- Particle physics to show the energy of particles made in accelerators, often in GeV or TeV
- Astrophysics and space science to describe the energy of cosmic rays, x rays and gamma rays
- Solid state physics and electronics to express band gaps and energy levels inside materials and semiconductors
Even though it is not an official SI unit, the electronvolt is accepted for use with SI units and is standard in scientific papers, data tables and textbooks in these fields.
Example Conversions
Here are some simple conversion examples between electronvolts and joules, and between different electronvolt sized units.
Electronvolts to joules
| Energy | In joules (J) |
|---|---|
| 1 eV | ≈ 1.602 × 10−19 J |
| 10 eV | ≈ 1.602 × 10−18 J |
| 1 keV | ≈ 1.602 × 10−16 J |
| 1 MeV | ≈ 1.602 × 10−13 J |
| 1 GeV | ≈ 1.602 × 10−10 J |
Joules to electronvolts
- 1 J ≈ 6.242 × 1018 eV
- 1 × 10−13 J ≈ 0.624 GeV
Everyday style examples
- Visible light photons have energies of about 1 eV to 3 eV
- X rays from a hospital machine often have energies around 10 keV to 100 keV
- Particles in large accelerators like the LHC can reach energies of several TeV
Related Units
Electronvolt is one way to measure energy. Here are some related units:
- Joule (J) the main SI unit for energy, used in most science and engineering
- Erg an older unit used in the cgs system, 1 erg = 1 × 10−7 J
- Calorie (cal) a unit often used for food energy, 1 cal ≈ 4.184 J
- Kilowatt hour (kWh) a large energy unit used on electricity bills, 1 kWh = 3.6 × 106 J
All of these units, including the electronvolt, describe the same kind of thing energy but at very different size levels. Electronvolts are best for very small scale physics.
FAQs
What exactly is 1 electronvolt in joules?
One electronvolt is exactly 1.602 176 634 × 10−19 joule. This exact number is based on the defined value of the electric charge of the electron.
Why do scientists use electronvolts instead of joules?
For atomic and particle physics, the energies are extremely small. If scientists always used joules, they would have to write very tiny numbers with many zeros. Using electronvolts keeps the numbers short and easier to compare.
Is electronvolt an SI unit?
Electronvolt is not one of the basic SI units, but it is officially allowed for use with SI. It is very common and accepted in scientific work worldwide.
What is the difference between eV, keV, MeV and GeV?
They are all the same type of unit, just at different sizes. 1 keV is one thousand eV, 1 MeV is one million eV and 1 GeV is one billion eV. They help match the unit size to the size of the energy being measured.
Where do we see electronvolts in real life?
You do not see electronvolts on normal devices like batteries or electricity bills. But they are used behind the scenes in hospital x ray machines, computer chip design, solar cells, particle accelerators and astronomy research.
Can I convert electricity from volts to electronvolts?
Volts and electronvolts are different things. Volt measures electric potential and electronvolt measures energy. To get electronvolts, you need both the voltage and the charge of the particle. For one electron, energy in eV equals the number of volts it moves through.
Is electronvolt only for electrons?
No. The name comes from electrons, but the unit can be used for any particle or photon. If a particle with the same charge as an electron moves through one volt, it gains one electronvolt of energy.