Ch 24-3 Quiz

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Ch 24-3 Quiz

Post  helping on Tue Apr 14, 2009 1:12 am

Question 1: ((ln(factor))/(decay constant))/31536000

The number in the denominator is the amount of seconds in a year.

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Re: Ch 24-3 Quiz

Post  helping on Tue Apr 14, 2009 1:23 am

Question 2:

decays per day/(e^-("thousand years ago value"*365000*(.69315/(half life * 365))))

Answer is negative.

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Re: Ch 24-3 Quiz

Post  helping on Tue Apr 14, 2009 2:20 am

Question 3:

(9*10^9*(# of protons)*(1.6*10^-19)^2)/(distance)

Answer is positive.

Question 4:

((9*10^9*2*(# of protons)*(1.6*10^-19)^2)/distance)/(1.6*10^-13)

Answer is negative.


Good luck!

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Re: Ch 24-3 Quiz

Post  hey on Tue Apr 14, 2009 2:47 am

for number 4 y did you divide by 1.6E-13

hey
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Re: Ch 24-3 Quiz

Post  Helping on Tue Apr 14, 2009 12:20 pm

To convert to MeV, you multiply 10^6 to your usual 10^-19.

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4

Post  4 on Tue Apr 14, 2009 8:39 pm

I am getting # 4 WRONG

any help

4
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Re: Ch 24-3 Quiz

Post  helping on Tue Apr 14, 2009 9:03 pm

Number 4 is exactly like number 3 except that you multiply by two in the numerator and then divide the whole answer by 1.6E-13.

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4

Post  a on Tue Apr 14, 2009 9:11 pm

thanx a lot i got it now Smile

a
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Question 2

Post  Guest786 on Wed Apr 15, 2009 1:23 am

I am having problems figuring out number 2. I am using the formula provided above but it doesn't seem to work for me.

The half life of radioactive C14 nuclei is 5730 years. If the activity of a sample today is 24.61 decays per day, what was its activity 2.426 thousand years ago (in decays per day) (sheet 23,23') ? Indicate with a negative (positive) sign whether the number of radioactive nuclei as a function of time obeys the same (a different) exponential decay law as the activity as a function of time.

24.61/(e^(2.426*365000*9.69315/(5730*365)))) and I get my answer as -18.3510....what am i doing wrong?

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question 2 correction

Post  Guest786 on Wed Apr 15, 2009 1:24 am

this is what i did



24.61/(e^(2.426*365000*(.69315/(5730*365)))) and I get my answer as -18.3510....what am i doing wrong?

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Re: Ch 24-3 Quiz

Post  guest123 on Wed Apr 15, 2009 2:30 am

this is what i did



24.61/(e^(2.426*365000*(.69315/(5730*365)))) and I get my answer as -18.3510....what am i doing wrong?


ur missing a (-) sign after e^
it should be 24.61/(e^-(2.426*365000*(.69315/(5730*365))))

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Number 2

Post  Money23 on Wed Apr 15, 2009 10:53 am

Hey guys, I got the other 3 but for some strange reason im stuck on number 2. I tried to follow all the appropriate steps but keep getting an incorrect answer on mapleTA @ . This is my question...
2) The half life of radioactive C14 nuclei is 5730 years. If the activity of a sample today is 20.85 decays per day, what was its activity 8.613 thousand years ago (in decays per day) (sheet 23,23') ? Indicate with a negative (positive) sign whether the number of radioactive nuclei as a function of time obeys the same (a different) exponential decay law as the activity as a function of time

This is what i did...
20.85/ (e^-(8.163 * 365000 * (.69315/ (5730* 365))))= 55.97
mapleTA says im wrong. Maybe one of you guys can help me Smile .
Obviously im making a retarded mistake somewhere and I cant seem to figure out where lol so pleaseee. Will be eternally grateful!!! Like a Star @ heaven

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n/m

Post  Money23 on Wed Apr 15, 2009 11:04 am

Nevermind guys i got it!!! finally... cheers

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Re: Ch 24-3 Quiz

Post  asda on Thu Apr 16, 2009 2:53 pm

Can you explain number one please?

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Re: Ch 24-3 Quiz

Post  zZtoP on Tue May 12, 2009 5:22 pm

ditto, can someone please explain the mathematical formulation that brings one to the answer for number one?

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Re: Ch 24-3 Quiz

Post  PhyPhy on Tue May 12, 2009 10:56 pm

You use the formula on Sheet 23 N(t)=Noe^-lambdat
divide No over so you get N/No which is the same thing as the factor of decrease or increase.
N/No = e^-lamdat
ln(N/No) = lamdat
(ln(N/No)/lamda) = t
and once you solve for t you gotta convert it to years which is the big number you divide by.

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Re: Ch 24-3 Quiz

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