Half Life Lab

Half-life lab Introduction: When an archeologist unearths a lost civilization, or the remains of a once great king, how does he know when that king lived? He can get an approximate guess from the architecture of the buildings or from the items left in the tomb, but such guesses are mere speculations. In order to get a more exact idea of when the king lived, or when the civilization flourished, scientists perform half-life calculations. Today’s lab activity is designed to show you (in basic terms) what half life is and how it can be used to accurately date objects buried in the earth. Materials: Pennies Data Sheet (you’re holding it) Procedure: 1) Obtain 16 pennies from your instructor 2) Divide the pennies among the members of your lab group. It does not matter if one member has more pennies than another member. 3) Flip every coin in the group once. 4) Record the number of “heads” on the data table below in the row label “1st trial”. 5) Next flip one coin for each “head” that was flipped in the previous round of flipping. Example: If the first round of coin flipping yielded 8 heads (and it should be near that because you flipped 16 coins and there’s a 50/50 chance of flipping a head) then in the next round you would flip only 8 coins. 6) Repeat this process until you have no more coins to flip. 7) Repeat steps 3-6 twice more and record your data in the 2nd and 3rd trial rows. Does it take the same number of “rounds” to eliminate your coins every time? Why not? (don’t write the answer here, just discuss it with your group) Get Creative: 16 coins are not really enough coins to accurately measure a “half life”. Devise a way to simulate the flipping of 128 coins in the first round. Explain your procedure to your instructor before moving on. Record this data in the “128 trial” row. Create more boxes if you need to. Do this once more and record your data in the “128 Part II” row. What do you notice about this data? Trial

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1st trial 2nd trial 3rd trial 128 trial 128 Part II Class _____ Questions to be addressed in the conclusion: 1) Why did the trials that started with only 16 coins yield accurate results? 2) What is noticeable about the two 128 trials? Is it more accurate? 3) What is noticeable about the whole class trial? Is it more accurate? 4) What happens to accuracy as you increase the number of coins you start with?

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Flips

5) Would you expect high accuracy if you started with 6.022*1023 coins? Why?