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# half life watch

1. can sum1 do this question i really don't understand it:

the idea of half- life can be used to find the age of the rock.

radioactive uranium is trapped in a rock when rock is formed.
the half-life of uranium is 4500million years.

explain how you can find the age of the rock. (4)
2. (Original post by starcrossed)
can sum1 do this question i really don't understand it:

the idea of half- life can be used to find the age of the rock.

radioactive uranium is trapped in a rock when rock is formed.
the half-life of uranium is 4500million years.

explain how you can find the age of the rock. (4)
the half life of an object is the time taken for the radioactivity to halve. if you know the half life, you can work out the age of the rock by measuring the radioactivity, then working out how long it must have taken for the rock to decrease in radioactivity to its current level.
3. (Original post by allisandro)
the half life of an object is the time taken for the radioactivity to halve. if you know the half life, you can work out the age of the rock by measuring the radioactivity, then working out how long it must have taken for the rock to decrease in radioactivity to its current level.
thanks, i think i understand it now.
4. has ne1 else got any ways they would answer this question?

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