Solving Problems in Science

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Solving Problems in Science
International Junior Science Olympiad (IJSO)
Dr. Yu-San Cheung yscheung_at_cuhk.edu.hk Department
of Chemistry The Chinese University of Hong Kong
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Scientific Method
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Precision vs. Accuracy

• Precision(???)
• representing the agreement between repeated
  measurements of the same quantity
• Accuracy(???)
• representing the agreement between a measured
  value and the true quantity

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• Significant figure
• Multiplication and division keep the smaller
  number of significant figure
• Decimal place
• Addition and subtraction keep the smaller number
  of decimal place

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Exercise

• Determine the answer for (a) to (f) below. Use
  the correct number
• of significant digits in your answer.
• 7.2 mm x 1.56 mm
• 99.5 cm2 x 0.0084 cm
• 63.6 g/ 2.7 cm3
• 288 g/16.9 cm3
• 0.001 g 5.3 g 162 g
• 32.58 cm3 5.2 cm3

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Control Experiment
A method of scientific investigation to
demonstrate a cause and effect hypothesis. For
example, a phenomenon occurs after a certain
treatment is given to a subject, and that the
phenomenon does not occur in the absence of the
treatment.
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Variable in Control Experiment

• Dependent variable
• Quantity to be measured
• Quantity which is thought to be affected during
  the experiment
• Results of the experiment.
• Independent variable
• Quantity to be varied
• Quantity which is thought to affect the dependent
  variable(s)
• Quantity which can be manipulated or controlled.
• Controlled variable
• Quantity kept constant or unchanged.

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Experiment Set-up
Control Group vs Experiment Group

• Control Group
• Set-up
• Procedures
• Control Variables

• Experiment Group
• Set-up
• Procedures
• Control Variables
• Independent Variables

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A Photosynthesis(????) Problem
The following experiment is designed to find out
whether light is necessary of photosynthesis.

1. What is the hypothesis of this experiment?
2. If starch is present in region A but absent in
   region B after exposing the plant to sunlight for
   several hours, what would your conclusion be?
3. Which region is the control? Explain briefly.