Joule to Electron Volt
J
eV
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Quick Reference Table (Joule to Electron Volt)
| Joule (J) | Electron Volt (eV) |
|---|---|
| 1 | 6,241,509,074,460,762,607.77624098093044589989 |
| 10 | 62,415,090,744,607,626,077.76240980930445899887 |
| 100 | 624,150,907,446,076,260,777.6240980930445899887 |
| 1,000 | 6,241,509,074,460,762,607,776.24098093044589988697 |
| 4,184 | 26,114,473,967,543,830,750,935.79226421298564512707 |
| 3,600,000 | 22,469,432,668,058,745,387,994,467.53134960523959307723 |
About Joule (J)
The joule (J) is the SI unit of energy, defined as the work done when a force of one newton displaces an object one meter in the direction of the force. It is also the energy dissipated as heat when one ampere flows through one ohm of resistance for one second. The joule underpins all other energy units in science: calories, watt-hours, and electron volts are all defined relative to it. At human scale, one joule is a small quantity — lifting a 100 g apple by one meter requires about one joule.
Lifting a medium apple (100 g) by 1 meter requires about 1 J. A typical sneeze releases roughly 1 J of kinetic energy.
Etymology: Named after English physicist James Prescott Joule (1818–1889), who experimentally established the mechanical equivalent of heat, demonstrating that work and heat are interconvertible forms of the same quantity.
About Electron Volt (eV)
An electron volt (eV) is the kinetic energy gained by a single electron accelerating through an electric potential difference of one volt — equal to approximately 1.602 × 10⁻¹⁹ joules. It is the natural energy unit of particle physics, atomic physics, and chemistry, where joules would yield unwieldy powers of 10. Photon energies, ionisation energies, bandgaps in semiconductors, and masses of subatomic particles (via E = mc²) are all expressed in eV, keV, MeV, or GeV.
Visible light photons carry 1.8–3.1 eV of energy. The proton rest mass is 938 MeV. The Large Hadron Collider accelerates protons to 6.5 TeV (6.5 × 10¹² eV).
Joule – Frequently Asked Questions
Why is the joule named after James Prescott Joule and not after a more famous physicist?
Joule was the first to prove experimentally that heat and mechanical work are the same thing — he measured the temperature rise of water churned by a falling weight. That 1845 brewery-funded experiment settled a centuries-old debate and earned the SI energy unit his name in 1889, well before units were named after Einstein or Feynman.
How many joules are in a kilowatt-hour on an electricity bill?
Exactly 3,600,000 joules. A kilowatt-hour is simply 1,000 watts sustained for 3,600 seconds. Utilities chose kWh because quoting home energy use in megajoules (e.g., "your fridge used 129.6 MJ this month") would confuse most customers.
What everyday action uses about one joule of energy?
Lifting a medium apple one meter off the ground takes roughly 1 J. Clicking a computer mouse uses about 1.5 mJ (0.0015 J), a heartbeat expends ~1 J, and a single typed keystroke on a mechanical keyboard is around 10–40 mJ. A joule is a surprisingly tiny amount of energy at human scale.
What is the difference between a joule and a watt?
A joule measures total energy; a watt measures the rate of energy flow (power). One watt equals one joule per second. A 60 W lightbulb consumes 60 joules every second — leave it on for an hour and it uses 216,000 J (0.06 kWh). Think of joules as liters of water and watts as the flow rate of the tap.
How does the joule relate to the calorie?
One thermochemical calorie equals exactly 4.184 joules. The "calorie" on food labels is actually a kilocalorie (4,184 J). So a 2,000-Calorie daily diet supplies about 8.4 million joules — enough energy to lift a small car roughly 850 meters straight up, if your body were 100% efficient (it is not).
Electron Volt – Frequently Asked Questions
Why do particle physicists use electron volts instead of joules?
Because subatomic energies in joules have absurdly small exponents — a visible-light photon carries about 3 × 10⁻¹⁹ J, but a convenient 1.9 eV. The electron volt is scaled to the quantum world, making numbers human-readable. It also doubles as a mass unit (via E = mc²): a proton is 938.3 MeV/c², far easier to work with than 1.673 × 10⁻²⁷ kg.
How much energy in electron volts does visible light carry?
Visible light photons range from about 1.65 eV (deep red, 750 nm) to 3.1 eV (violet, 400 nm). Green light, where the human eye is most sensitive, sits around 2.3 eV. Ultraviolet photons start at 3.1 eV and can exceed 100 eV in the extreme UV. These energies are why UV can damage DNA (breaking molecular bonds of 3–5 eV) while visible light cannot.
What is the relationship between electron volts and semiconductor bandgaps?
A semiconductor's bandgap — the minimum energy to free an electron from its bond — is expressed in eV. Silicon has a bandgap of 1.12 eV, gallium arsenide 1.42 eV, and gallium nitride 3.4 eV. The bandgap determines which wavelengths of light a solar cell can absorb and what color an LED emits. Lower bandgap means longer-wavelength (redder) light.
How many electron volts does the Large Hadron Collider produce?
The LHC accelerates protons to 6.5 TeV (6.5 × 10¹² eV) per beam, giving collisions a center-of-mass energy of 13 TeV. That sounds enormous, but 13 TeV is only about 2 microjoules — the kinetic energy of a flying mosquito. The power of the LHC lies in concentrating that energy into a space a million times smaller than an atom.
How do you convert electron volts to joules?
Multiply by 1.602 176 634 × 10⁻¹⁹. So 1 eV = 1.602 × 10⁻¹⁹ J, 1 keV = 1.602 × 10⁻¹⁶ J, and 1 MeV = 1.602 × 10⁻¹³ J. This conversion factor is exactly the elementary charge in coulombs, because an electron volt is defined as the energy gained by one electron charge crossing one volt of potential.