I’ve been reading about HL, but I still don’t get why would you use it. So, if half life of coffee is 5h, how that info is relevant when we know that full life is 10 (roughly)? On top of that, how do you get the half-life of a material other than waiting to be completely ‘dead’ and say, ok full life is X, the half life is X/2.
Also, let’s take uranium which in Earth’s crust has a half-life of almost 4.5 billion years.. how did we get this number?
Thank you!
In: Chemistry
>So, if half life of coffee is 5h, how that info is relevant when we know that full life is 10 (roughly)?
It is not 10 hours.
Lets start with 1 shot of coffee. That’s around 20mg of caffine in your blood.
5 hours after drinking it there is 10mg of caffine in your blood.
10 hours after there is 5mg of caffine in your blood.
15 hours after there is 2.5mg
and so on.
It’s a half life because after the amount keeps halving every time, it doesn’t go down at the same rate from 100% to 0.
To understand what’s going on, imagine simultaneously flipping 100 coins. Any coin that lands heads you remove and flip the remaining coins again. After the first flip you’ll have around 50 coins left, after the 2nd flip you’ll have 25 and so on. In this case the coins have a half-life of 1 flip.
>Also, let’s take uranium which in Earth’s crust has a half-life of almost 4.5 billion years.. how did we get this number?
For this you can measure how radioactive a sameple of a substance is, use that to calculate the rate that radioactive atoms are individually decaying, then use that to calculate how long it would take half the atoms in the sample you have to decay.
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