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Glossary Science & Engineering

Half-life

A half-life is the time it takes for half of a quantity to decay or disappear, whether a radioactive isotope or a drug in the body.

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In more detail

The remaining amount is N₀ × (½)^(t / T). 80 g with a half-life of 5 days is 10 g after 15 days, three half-lives. Caffeine in the body has a half-life of roughly five hours.

Try these tools

Half-Life Calculator

Solve for remaining quantity, initial quantity, elapsed time, or half-life itself using N = N0 * (1/2)^(t / half-life).

Caffeine Calculator

Add your coffee, tea, energy drinks and more to total your daily caffeine.

See also

  • Glossary Exponent
    An exponent says how many times to multiply a base by itself: in `2³` the base is 2, the exponent is 3, and the value is 8.
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