| Terajoules (TJ) | Electronvolts (eV) |
|---|---|
| 1 Terajoule | 6.24150907446 × 1030 eV |
| 2 Terajoules | 1.24830181489 × 1031 eV |
| 3 Terajoules | 1.87245272234 × 1031 eV |
| 4 Terajoules | 2.49660362978 × 1031 eV |
| 5 Terajoules | 3.12075453723 × 1031 eV |
| 10 Terajoules | 6.24150907446 × 1031 eV |
| 20 Terajoules | 1.24830181489 × 1032 eV |
| 25 Terajoules | 1.56037726862 × 1032 eV |
| 50 Terajoules | 3.12075453723 × 1032 eV |
| 100 Terajoules | 6.24150907446 × 1032 eV |
| Reference | Terajoules (TJ) | Electronvolts (eV) |
|---|---|---|
| One food calorie (kcal) | 0.000000004184 TJ | 2.61145 × 1022 eV |
| An AA alkaline battery | 0.00000001 TJ | 6.24151 × 1022 eV |
| Daily adult food intake | 0.000008368 TJ | 5.22289 × 1025 eV |
| One unit on an electricity bill | 0.0000036 TJ | 2.24694 × 1025 eV |
| A lightning strike | 0.001 TJ | 6.24151 × 1027 eV |
The terajoule is a unit of energy equal to a thousand gigajoules, or 1,000,000,000,000 joules. Its symbol is TJ. It is the unit in which countries account for their energy, and it appears far more often in official statistics than in any engineering catalogue, because it is sized for the annual consumption of a town rather than of a machine.
International energy accounting runs on it. The International Energy Agency publishes national energy balances in terajoules, and greenhouse-gas inventories submitted under the United Nations climate framework report fuel use in the same unit. Emission factors are expressed to match: burning a terajoule of natural gas releases about 56 tonnes of carbon dioxide, diesel about 74, and hard coal about 95, which turns any energy figure directly into an emissions figure.
Generation is described here too. A three-megawatt wind turbine running at a realistic capacity factor produces roughly 33 terajoules in a year. A single cargo of liquefied natural gas in a large carrier holds close to 3800 terajoules, which is why one shipment can cover a small country's gas demand for weeks. Grid-scale batteries, by contrast, are still measured in fractions of a terajoule.
Destructive energy reaches the scale as well. A kilotonne of TNT equals 4.184 terajoules exactly, so the bomb dropped on Hiroshima released roughly 63 terajoules. An earthquake of magnitude five radiates about two terajoules of seismic energy, and each whole step up the magnitude scale multiplies that by about thirty-two, which is what makes a magnitude seven event a thousand times the size of a magnitude five one.
The unit also marks a boundary in how energy is discussed. Below it, quantities belong to buildings, vehicles and appliances, and people argue about efficiency. At and above it, quantities belong to policy: fuel imports, subsidy schemes, emission targets and grid planning. The same physics is being measured, but the terajoule is where the conversation stops being technical and becomes political.
Above the terajoule the ladder continues with the petajoule, used for whole national sectors, and the exajoule, used for world totals: global primary energy consumption runs to something over 600 exajoules a year. Reading any of these back down is a matter of moving the decimal point three places at a time.
One terajoule equals 1,000,000,000,000 joules, about 277.8 megawatt-hours, or about 239 gigacalories.
The electronvolt is a unit of energy equal to the work done on a single electron moved through a potential difference of one volt. Its symbol is eV. Since the 2019 redefinition of the SI it has an exact value, 1.602176634 times ten to the power minus nineteen joules, because the elementary charge itself is now a defined constant.
It exists because the joule is hopelessly large for the atomic world. A single visible photon carries between about 1.6 and 3.3 electronvolts, and expressing that in joules requires nineteen leading zeros. Working in electronvolts lets a physicist state the energy of a chemical bond, an atomic transition or a subatomic collision as a number between one and a few, which is what a unit is supposed to do.
The scale organises whole disciplines. Chemistry lives at a few electronvolts, the energy of bonds and of the visible and ultraviolet photons that break them. X-rays occupy kiloelectronvolts. Nuclear physics works in megaelectronvolts, the scale of binding energies and radioactive decay. Particle physics uses gigaelectronvolts, where the proton's rest mass is 0.938, and teraelectronvolts at the Large Hadron Collider, whose protons carry 6.8 each.
Mass is quoted in the same unit through the mass-energy relation. A particle's rest mass is given in electronvolts divided by the speed of light squared, and physicists routinely drop the divisor and simply say that the electron is 511 kiloelectronvolts. The Higgs boson is 125 gigaelectronvolts on the same convention.
Semiconductor engineering depends on it. The band gap that determines what a material does electrically and optically is an energy in electronvolts: about 1.1 for silicon, 3.4 for gallium nitride, and this single number decides whether a device is a solar cell, a transistor or a blue light-emitting diode.
Astronomy inherits the convention for high-energy photons, so gamma-ray telescopes report observations in gigaelectronvolts and teraelectronvolts rather than in wavelengths.
Particle accelerators are named after the energies they reach, which is why their names track the prefixes. The Cockcroft-Walton machine that first split a nucleus in 1932 worked at a few hundred kiloelectronvolts; the Bevatron of the 1950s reached billions and found the antiproton; and the Large Hadron Collider brings protons to 6.8 teraelectronvolts each. Cosmic rays put all of this in perspective by arriving with energies up to 10 to the twentieth electronvolts, tens of millions of times more than any machine can produce, though only a handful of such particles strike the Earth in a century over a square kilometre.
One electronvolt equals about 1.602 times ten to the power minus nineteen joules, or roughly 3.83 times ten to the power minus twenty calories.