Half time (physics)

Half time in physics refers to the time taken for half of the atoms to decay in a radioactive substance. Let's pretend we have 100 jelly beans in a jar.

Now imagine that each jelly bean has a little light inside of it, and the light goes out when that jelly bean 'decays'. The time it takes for half of the jellybeans to lose their light is what we call the half-time.

So let's say every minute, ten jelly beans lose their light because they decay. After one minute, 10/100 of the jelly beans have decayed, which means we have 90 left.

After two minutes, another 10/90 (or about 11%) of the jelly beans decay, leaving us with 80.

This keeps on happening every minute –- after three minutes, we’re left with 70 jellybeans, and after four minutes, we’re only left with 60.

Half-time is the time until we get to the point where exactly half of the jellybeans (in this case 50) have lost their light and 'decayed'.

So in our example, the half-time would be between two and three minutes, as we reach that halfway point after about 2.5 minutes.

It has many applications in physics, from determining the age of rocks to measuring the effectiveness of medication.