Idea 6of 7Builds onThree kinds of leak
The halving clock
A tracer reads 800. Six hours later, 400. Then?
Today you'll discover
- what a radioactive sample does in a fixed time
- why the next step is not the same amount
- the name of the clock
Think first800 counts, then 400 six hours later
The reading fell from 800 to 400 in six hours. Six more hours: what will it read?
Predict first, then press Next. Compare each bar with the one before it.
A row of bars, each half the height of the one before, with a clock in the corner. After a prediction, more bars appear with the fractions half, quarter, eighth along the bottom, and the clock is named. The last step switches to an eight-day isotope and asks what remains after three half-lives.
See the whole ideathe big idea and the key word, in one place
The big idea
Every half-life halves what is left: a fixed fraction.
Easy to get wrongTwo half-lives do not finish a sample. They leave a quarter. Halving never reaches zero; it only shrinks.
Key word
- half-life
- the time for half of the nuclei in a radioactive sample to decay; fixed for each isotope
About this modelEach half-life halves what is left. Halving never reaches zero; it only shrinks.
Each half-life halves what is left. Halving never reaches zero; it only shrinks.
Ready to use it?
- Find what remains of a sample after a given number of half-lives.