Investigation
20A
Half-Life
Experiment:
Coin Toss
What is a half-life? What does it measure?
How can we determine the age of fossils?
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Investigation 20A:Half-Life Experiment: Coin Toss
Part 1: Simulating half-life: Short version
This experiment is quite simple. It only involves
flipping coins and graphing the results.
1. Start with 10 pennies.
Call this “t = 0” on your graph, and plot a “10” on the y axis.
2. Toss all 10 pennies on the ground or on the table.
Remove all pennies that turn up tails.
These will be the decayed atoms.
3. Count the remaining pennies and plot the number.
This point will be at “t = 1” on the x axis.
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Investigation 20A:Half-Life Experiment: Coin Toss
Part 1: Simulating half-life: Short version
4. Repeat Steps 2 and 3.
Plot this at “t = 2” on the
x axis.
5. Repeat Steps 2 and 3
until all the pennies have
“decayed.”
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Investigation 20A:Half-Life Experiment: Coin Toss
Half-life
Half-life (t1/2): the time it takes
for half of the atoms in a
sample to decay.
Every radioactive isotope has
a different half-life.
Carbon dating is based
on the knowledge that t1/2 for
carbon-14 is 5,730 years.
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Investigation 20A:Half-Life Experiment: Coin Toss
Half-life
Ratio
not to scale
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t1/2
t1/2
t1/2
Investigation 20A:Half-Life Experiment: Coin Toss
Part 2: Simulating half-life: Long version of Part 1
Repeat the experiment
from Part 1, except use
100 pennies.
Continue running until
all the pennies “decay.”
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Investigation 20A:Half-Life Experiment: Coin Toss
Part 3: Simulating half-life: Long version of Part 2
1. Repeat the experiment from Part 1,
using only 10 pennies.
2. Now repeat this experiment a total of 10 times. Add the data from
each of the 10 experiments, and plot this on a new graph.
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Investigation 20A:Half-Life Experiment: Coin Toss
Part 3: Simulating half-life: Long version of Part 2
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Investigation 20A:Half-Life Experiment: Coin Toss
Part 4: Thinking about what you have learned
1. How smooth is the graph from
Part 1? How about Part 2?
How about Part 3?
2. What similarities do you notice
about the graphs from Parts 2
and Part 3? Why is that?
3. How would you make this
experiment even more precise?
Your data should be similar to this.
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Investigation 20A:Half-Life Experiment: Coin Toss
• Half-life is only dependent on
the type of atom present.
• Half-life has nothing to do
with how many atoms there
are, how close they are to
each other, what time it is,
or any other variables.
Running 10 experiments with 10 pennies each is exactly the same
as running one half-life experiment with 100 pennies.
• No matter how many radioactive atoms you have, half
will decay after the half-life.
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Investigation 20A:Half-Life Experiment: Coin Toss