-- Posted by rosiewantspancakes at 6:12 am on Nov. 19, 2008 i have my science gcse exam tomorrow, and i just don't get half life. i understand vaguely what it means, sort of.. but i don't get how to work it out. also... if anyone can explain 'red shift' to me too.. that'd be great :) -- Posted by Medevac at 6:14 am on Nov. 19, 2008 okay let's say you've got a 100 balls and the half life of the balls is 50 years after 50 years you'll have 50 balls after 100 years you'll have 25 balls and so on just google it -- Posted by hi sarah at 6:16 am on Nov. 19, 2008 i can try but i don't want the be the thing that made you fail -- Posted by Tubbz at 6:16 am on Nov. 19, 2008 Basically the half life is the time period for half the radioactive nuclei to decay. Ie. Carbon -13 Half life 1000years So in a thousand years you'll have half the amount of carbon 13 as you did when you started. in 2000 1/4, in 3000 1/8 -- Posted by rosiewantspancakes at 6:16 am on Nov. 19, 2008 thankyou for replying :) yeah.. that's the part i understand, all the examples i have are like that. but when it comes to an exam.. past paper or something.. the question is like this: "A sample of charcoal from the stone age campfire contains 12 billion carbon-14 atons. approximately how many carbon-14 atoms would the sample have contained 6000 years ago? a) 6 billion b) 12 billion 3) 24 billion 4) 48 billion" and it's those sotrs of questions i don't know how to work out. :S -- Posted by Tubbz at 6:19 am on Nov. 19, 2008 With the question, is the half life of carbon-14 given? I'd assume it's 3 or 6 thousand years. -- Posted by Medevac at 6:19 am on Nov. 19, 2008 Quote: from rosiewantspancakes at 6:16 am on Nov. 19, 2008 thankyou for replying :) yeah.. that's the part i understand, all the examples i have are like that. but when it comes to an exam.. past paper or something.. the question is like this: "A sample of charcoal from the stone age campfire contains 12 billion carbon-14 atons. approximately how many carbon-14 atoms would the sample have contained 6000 years ago? a) 6 billion b) 12 billion 3) 24 billion 4) 48 billion"   and it's those sotrs of questions i don't know how to work out. :S wiki tells me the half life is 5,730 this is GCSE so im going to assume you take the half life to be 6000 you know that every 6000 years the samply halves, so 6000 years ago it would be double what it is now or 24million -- Posted by Medevac at 6:20 am on Nov. 19, 2008 Quote: from Medevac at 6:19 am on Nov. 19, 2008 Quote: from rosiewantspancakes at 6:16 am on Nov. 19, 2008 thankyou for replying :)    yeah.. that's the part i understand, all the examples i have are like that.    but when it comes to an exam.. past paper or something.. the question is like this:    "A sample of charcoal from the stone age campfire contains 12 billion carbon-14 atons.    approximately how many carbon-14 atoms would the sample have contained 6000 years ago?    a) 6 billion    b) 12 billion    3) 24 billion    4) 48 billion"      and it's those sotrs of questions i don't know how to work out. :S wiki tells me the half life is 5,730 this is GCSE so im going to assume you take the half life to be 6000   you know that every 6000 years the samply halves, so 6000 years ago it would be double what it is now or 24million eh i mean billion -- Posted by rosiewantspancakes at 6:21 am on Nov. 19, 2008 oh sorry, yeah another part of the question just before says "carbon-14 decays by emitting beta particles and it's half like is 5730 years." -- Posted by Tubbz at 6:21 am on Nov. 19, 2008 Quote: from Medevac at 2:20 pm on Nov. 19, 2008 Quote: from Medevac at 6:19 am on Nov. 19, 2008 Quote: from rosiewantspancakes at 6:16 am on Nov. 19, 2008 thankyou for replying :)   yeah.. that's the part i understand, all the examples i have are like that.   but when it comes to an exam.. past paper or something.. the question is like this:   "A sample of charcoal from the stone age campfire contains 12 billion carbon-14 atons.   approximately how many carbon-14 atoms would the sample have contained 6000 years ago?   a) 6 billion   b) 12 billion   3) 24 billion   4) 48 billion"       and it's those sotrs of questions i don't know how to work out. :S    wiki tells me the half life is 5,730    this is GCSE so im going to assume you take the half life to be 6000  you know that every 6000 years the samply halves, so 6000 years ago it would be double what it is now    or 24million eh i mean billion ^^^^^ this 24 bil if they give you the Half life as 6k. They've changed GCSE since I did it so you may need to know certain half lives. -- Posted by Tubbz at 6:24 am on Nov. 19, 2008 Wait, does it want it exact or does it actually give you options? because I make it 24.8 x10^9 -- Posted by rosiewantspancakes at 6:26 am on Nov. 19, 2008 they give you options. "A sample of charcoal from the stone age campfire contains 12 billion carbon-14 atons. approximately how many carbon-14 atoms would the sample have contained 6000 years ago? a) 6 billion b) 12 billion 3) 24 billion 4) 48 billion" -- Posted by Tubbz at 6:30 am on Nov. 19, 2008 if it gives you options it's 24.  I don't think they usually do though, what are you doing? Dual award? -- Posted by rosiewantspancakes at 6:33 am on Nov. 19, 2008 yeah, i am. it's multichoice paper too, so at least that's a consilation! -- Posted by Tubbz at 6:36 am on Nov. 19, 2008 Quote: from rosiewantspancakes at 2:33 pm on Nov. 19, 2008 yeah, i am. it's multichoice paper too, so at least that's a consilation! I say B. I always pick a letter at the start of any multi choice exam to use as my guess.