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Lecture 2-Experimental Design


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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

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Lecture 2-Experimental Design

  1. 1. Experimental Design Chapter 3 Jump to first page
  2. 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 Jump to first page
  3. 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. Jump to first page
  4. 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 Jump to first page
  5. 5. Creating and Testing a Hypothesis Example: Radiation What do you/we know about radiation exposure? Create a hypothesis about radiation dose: Jump to first page
  6. 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? Jump to first page
  7. 7. Testing a Hypothesis How would you know if you have proven or disproven your hypothesis? How would you compare everyone’s results? Jump to first page
  8. 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? Jump to first page
  9. 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. Jump to first page
  10. 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 Jump to first page
  11. 11. Radiation Doses Absorbed Dose, rads 0 (control) 5,000 10,000 15,000 30,000 80,000 Jump to first page
  12. 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 Jump to first page
  13. 13. Exposure Map Within the Gammacell 220 Jump to first page
  14. 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) Jump to first page
  15. 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. Jump to first page
  16. 16. Science – It’s Great Stuff Jump to first page
  17. 17. Summary Design a scientific experiment Calculate exposure times Limit experimental error Collect data Analyze data Present results Write a technical report Jump to first page