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Electronvolt

What Is Electronvolt?

An electronvolt is a very small unit of energy. Scientists use it to talk about the energy of tiny things like electrons, atoms and particles in space or in big machines like particle colliders. It helps make very small energies easier to read and compare than using joules alone.

Definition

An electronvolt, written as eV, is the energy that one electron gets or loses when it moves through an electric potential difference of one volt.

In the International System of Units, or SI units, energy is measured in joules. One electronvolt is equal to:

1 eV ≈ 1.602 × 10-19 joule

This number is extremely small, so electronvolts are useful when we talk about single atoms, light particles and nuclear reactions.

History / Origin

The idea of the electronvolt came from early studies of electricity and electrons in the late 1800s and early 1900s.

  • Scientists learned that electrons carry a fixed electric charge.
  • They also used the volt to measure electric potential, or how strongly charges are pushed.
  • They combined these ideas to make a simple unit for the energy of one electron moved through one volt.

The electronvolt quickly became popular in atomic, nuclear and later particle physics, because it made the math and the numbers easier to work with than always using joules.

Symbol & Abbreviation

The standard symbol for electronvolt is:

  • eV for electronvolt

Larger amounts of energy often use prefixes in front of eV:

  • eV electronvolt
  • keV kiloelectronvolt 1 keV = 1 000 eV
  • MeV megaelectronvolt 1 MeV = 1 000 000 eV
  • GeV gigaelectronvolt 1 GeV = 1 000 000 000 eV
  • TeV teraelectronvolt 1 TeV = 1 000 000 000 000 eV

These prefixes help write very large or very small energies in a clean and simple way.

Current Use Around the World

The electronvolt is not an official SI unit, but it is accepted for use with SI and is used worldwide in many fields of physics.

Common areas that use electronvolts include:

  • Atomic physics to describe the energy of electrons in atoms and ions
  • Nuclear physics to measure the energy released in nuclear reactions and decays
  • Particle physics to describe the energy and mass of particles in accelerators like the Large Hadron Collider
  • Astrophysics and space science to talk about cosmic rays, X rays and gamma rays
  • Solid state physics to explain energy bands in materials and semiconductors

In these fields, scientists often write particle masses in eV divided by the speed of light squared, as eV/c2. This comes from Einstein’s famous relation E = mc2, which links energy and mass.

Example Conversions

Here are some helpful, rounded conversion examples between electronvolts and joules.

From electronvolts to joules

  • 1 eV ≈ 1.602 × 10-19 J
  • 1 keV = 1 000 eV ≈ 1.602 × 10-16 J
  • 1 MeV = 1 000 000 eV ≈ 1.602 × 10-13 J
  • 1 GeV = 1 000 000 000 eV ≈ 1.602 × 10-10 J

From joules to electronvolts

  • 1 J ≈ 6.242 × 1018 eV
  • 1 × 10-19 J ≈ 0.624 eV
  • 1 × 10-13 J ≈ 6.24 × 105 eV about 624 keV

Simple picture of the size

  • The energy of visible light photons is a few eV.
  • X ray photons are often in the range of thousands of eV keV.
  • Gamma rays and high energy particles can reach MeV, GeV or even TeV.

Electronvolt is one way to measure energy. Here are some related units and ideas.

  • Joule (J) the main SI unit of energy. All electronvolt values can be written in joules.
  • Volt (V) the unit of electric potential. The definition of 1 eV uses 1 volt and the charge of one electron.
  • Calorie (cal) an older unit for heat energy, mostly used in food and chemistry, not in particle physics.
  • Kilowatt hour (kWh) a unit of energy used for electricity bills, very large compared with electronvolts.
  • Electronvolt per particle sometimes used to describe average energy per particle in a gas or plasma.

In high energy physics, mass is often described in eV/c2 to show how mass and energy are closely linked.

FAQs

What is an electronvolt in simple words?

An electronvolt is the tiny amount of energy an electron gains or loses when it moves through an electric push of one volt. It helps describe the energy of very small things like atoms and particles.

Is electronvolt an SI unit?

No, electronvolt is not one of the base SI units. The official SI unit for energy is the joule. However, the electronvolt is accepted for use with SI and is widely used in physics.

Why do scientists use electronvolts instead of joules?

For atomic and particle physics, the energies are extremely small when written in joules. Using electronvolts makes the numbers easier to read and work with, so scientists can compare and calculate more clearly.

How is electronvolt different from volt?

The volt, V, is a unit of electric potential, like how strong an electric push is. The electronvolt, eV, is a unit of energy. One electronvolt is the energy gained by one electron moving through a potential difference of one volt.

How big is 1 eV compared to everyday energy?

One electronvolt is extremely small. It is about 1.6 × 10-19 joule. A simple action like dropping a small ball from your hand has many billions of billions of times more energy than 1 eV.

How do I convert between eV and joule?

Use these simple rules:

  • To go from eV to joule, multiply by 1.602 × 10-19.
  • To go from joule to eV, multiply by about 6.242 × 1018.

Where are electronvolts used in real life?

Electronvolts are used in designing X ray machines, studying radiation from the Sun and stars, building particle accelerators, making better computer chips and LEDs, and understanding nuclear energy and medical imaging.

What are keV, MeV and GeV?

These are larger units based on the electronvolt.

  • 1 keV is 1 000 eV.
  • 1 MeV is 1 000 000 eV.
  • 1 GeV is 1 000 000 000 eV.

They help write big energies, like those in nuclear reactions and particle collisions, in a short and simple way.

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