Half-life
This original textbook reading covers part of the AP topic. Follow the AP course outline for complete topic instruction and practice.
- Half-life
Often written as , it is the time required for a variable to be halved, compared to its initial condition. Variables can include mass, concentration, money, etc.
- Related Glossary Terms
Glossary and deeper reading · 1 refreshers
These editorial refreshers supplement the reading. Definitions and examples are added guidance; original source wording and recorded answers remain in their original context.
-
Half-life
A half-life is the time required for a positive exponentially decaying quantity to fall to half its current amount. For y(t)=y₀eᵏᵗ with k<0, it equals ln 2 divided by −k. For example, a quantity with half-life 3 hours falls to one quarter of its initial amount after 6 hours. The same half-life applies from any starting time within the exponential model.