00:01
Right, so this question we're looking at the decay of uranium 238, and we know that the earth at a start has some amount of uranium 238, right, some amounts.
00:14
And after some time, after its formation, and today, we have a little bit left, right, because most of it, some of it has decay.
00:27
So we want to find out why it's the fraction, right, of this decay.
00:33
And first of all we need the half -life of uranium 238 that is given as 4 .468 times 10 power of 9 years.
00:49
This is years.
00:53
Now we know that from the decay equation that the amount of uranium 238 at any point in time t is equal to the initial amount multiplied by half, power of t over t half.
01:14
In order to get a fraction left, we divide by n -knot.
01:21
And we get half t over t -half, right? on the right side, we can solve for this very simply.
01:29
Since we are all given the values over here, our t is 4 .5, understand to power 9, and our t -half is 4 .468, 10 to power 9, we get approximately 0 .5.
01:48
So this is the fraction of uranium 23 that still exists today after decaying for 4 .5 times 10 % of 9 years...