Lecture 2-Experimental Design Define the scientific method Learn how to design a scientific experiment calculate exposure times limit experimental error collect data analyze data present results write a technical report

1. Experimental
Design
Chapter 3
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2. Objectives
Define the scientific method
Learn how to
design a scientific experiment
calculate exposure times
limit experimental error
collect data
analyze data
present results
write a technical report
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3. The Scientific Method
The process by which scientists, over
time, attempt to build an accurate
representation of the world.
Who we are and what we believe can
influence our perceptions and our
interpretations of the world around us.
As a result, scientists use standard
procedures and criteria to minimize
those influences (biases) when
developing a theory.
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4. The Four Steps
Observe and describe a phenomenon or
group of phenomena
Formulate an hypothesis to explain the
phenomena
Use the hypothesis to
Predict the existence of other
phenomena, or
To predict quantitatively the results of
new observations
Test the predictions by several
independent experimenters and properly
performed experiments
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5. Creating and Testing a
Hypothesis
Example: Radiation
What do you/we know about
radiation exposure?
Create a hypothesis about
radiation dose:
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6. Designing a Scientific
Experiment
How would you test your
hypothesis?
What end result would you look
for?
How might you bias your
experiment?
How would you minimize it?
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7. Testing a Hypothesis
How would you know if you have
proven or disproven your
hypothesis?
How would you compare
everyone’s results?
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8. Reporting Results
How would you report your
results?
Would you construct a table or a
graph?
How would you label it/them?
How would you present your
results?
Where do you go to find
instructions?
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9. An Experiment: Radiation
Effects on Pinto Beans
The experiment you are starting
today will do four things:
Demonstrate the use of one of our
irradiation facilities;
Make you familiar with the unit of
absorbed dose (the gray or rad);
Promote a class discussion on
experimental design; And,
Allow you to see the effects of
radiation on plant growth.
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10. Irradiated Pinto Beans
Irradiated in the OSU Radiation Center
60
Co gamma cell.
Each group of seeds was irradiated to
different doses.
Neither the students nor the instructor
knows the dose given to any of the
groups.
The groups have been named: Marvin,
Rhonda, Walter, Shiela, Betty, and Fred
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11. Radiation Doses
Absorbed Dose, rads
0 (control)
5,000
10,000
15,000
30,000
80,000
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12. GammaCell 220 60Co
A device for providing
uniform radiation doses
throughout a large
volume
Approximately 8” h by
6” wide
Several small sources
surround the irradiation
chamber
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13. Exposure Map
Within the
Gammacell 220
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14. Planting Directions
Plant 5 beans (of the same dose group)
in each Styrofoam cup
Label each cup with the name of the
student group and the bean seed
treatment (dose) group
Punch drainage hole(s) in each cup
Fill cup approximately 3/4 full with dry
potting soil
Using a pencil or stick, make holes in the
soil to a uniform depth (e.g., five bean
seeds, five planting holes)
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15. Planting Directions,
cont’d
Lightly pat soil over beans
Place styrofoam cups in the aluminum
baking pans..
Place baking pans on window sill
Fill baking pans with water
Periodically
water the plants in the same way.
Do not let the soil dry out completely
Do not over-water
observe the behavior and growth of the
seeds.
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16. Science – It’s Great Stuff
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17. Summary
Design a scientific experiment
Calculate exposure times
Limit experimental error
Collect data
Analyze data
Present results
Write a technical report
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