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/sci/ - Science & Math

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4157360 No.4157360 [Reply] [Original]

This part of the question concerns half-lives. Remember to show your working for any calculations.
What percentage of a sample of a radioactive isotope remains after two half-lives have passed?
If a rock initially contained 10 milligrams (mg) of a radioactive isotope, how many milligrams of the isotope remain after four half-lives?
If a sample contains 1.56% of its original radioactive isotope, roughly how many half-lives will have passed?
A radioactive isotope has a half-life of 4.5 billion years. What percentage of the original isotope would remain after 6.75 billion years has passed?


get me some university points

>> No.4157364

>What percentage of a sample of a radioactive isotope remains after two half-lives have passed?

After one half-life half of it is gone. After two all of it is gone. Easy peasy.

>> No.4157367

>>4157364
THANK YOU :D

>> No.4157380

>>4157367

Part of me wants to go along with your joke, but...

Wiki it.

>> No.4157391

>>4157380
I'm hoping OP left his thread long ago and won't see that.

>> No.4157410

>>4157364
That's shit, you are aware of that...

After two half lives, a quarter remains.

T*(1/2^n) where T is the total amount of isotope and n is the amount of half lives that have occurred.

>> No.4157411

>>4157410
>two half-lives mean a quarter
>implying 2 * 1/2 = 1/4

>> No.4157413

http://math.usask.ca/emr/examples/expdeceg.html

This is the explanation you are looking for OP.

>> No.4157414

>>4157411
Fail.

It's not 2*1/2.
It's 1/2*1/2.

Simplified to 1/2^n

>> No.4157454

more answers plox

>> No.4157466

>>4157414
Wrong, two half-lives make a whole-life. After a whole life, everything's gone. Just because this is a homework thread doesn't mean you have to try to fuck OP over.

>> No.4157473

>>4157466
Oh, of course.
You're trying to fuck the OP over.

OP: http://en.wikipedia.org/wiki/Half-life

To the right, there is a table.

Nice try, troll face.

>> No.4157478

>>4157414
>It's 1/2*1/2.

That's half of a half-life, you idiot.

>> No.4157484

>>4157478
Troll.

Read the wiki article.

>> No.4157506

>>4157484
WHY ARE YOU POSTING THIS SHIT. He came to us for answers! If he wanted to learn this shit off Wikipedia, he would've gone there first.

>> No.4157509

>>4157506
He's better off.

With trolls like you saying that a substance completely disappears after two half lives, he's better off going on wiki.