Solving Problems in Science International Junior Science Olympiad

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Solving Problems in Science International Junior Science Olympiad (IJSO) Dr. Yu-San Cheung yscheung@cuhk. edu.

Solving Problems in Science International Junior Science Olympiad (IJSO) Dr. Yu-San Cheung [email protected] edu. hk Department of Chemistry The Chinese University of Hong Kong 1

Scientific Method Modifying theory as needed Observation Hypothesis Experiment Analysis Theory Prediction Experiment Law

Scientific Method Modifying theory as needed Observation Hypothesis Experiment Analysis Theory Prediction Experiment Law 2

Precision vs. Accuracy Precision(精密度) -representing the agreement between repeated measurements of the same quantity

Precision vs. Accuracy Precision(精密度) -representing the agreement between repeated measurements of the same quantity Accuracy(準確度) -representing the agreement between a measured value and the true quantity 3

Significant figure: Multiplication and division: keep the smaller number of significant figure Decimal place:

Significant figure: Multiplication and division: keep the smaller number of significant figure Decimal place: Addition and subtraction: keep the smaller number of decimal place 4

Exercise Determine the answer for (a) to (f) below. Use the correct number of

Exercise Determine the answer for (a) to (f) below. Use the correct number of significant digits in your answer. a. 7. 2 mm x 1. 56 mm = b. 99. 5 cm 2 x 0. 0084 cm = c. 63. 6 g/ 2. 7 cm 3 = d. 288 g/16. 9 cm 3= e. 0. 001 g + 5. 3 g + 162 g = f. 32. 58 cm 3 – 5. 2 cm 3 = 5

Control Experiment A method of scientific investigation to demonstrate a cause and effect hypothesis.

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. 6

Variable in Control Experiment Dependent variable • Quantity to be measured; • Quantity which

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. 7

Experiment Set-up Control Group vs Experiment Group Control Group • Set-up • Procedures •

Experiment Set-up Control Group vs Experiment Group Control Group • Set-up • Procedures • Control Variables Experiment Group • Set-up • Procedures • Control Variables • Independent Variables 8

A Photosynthesis(光合作用) Problem The following experiment is designed to find out whether light is

A Photosynthesis(光合作用) Problem The following experiment is designed to find out whether light is necessary of photosynthesis. A. What is the hypothesis of this experiment? B. 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? C. Which region is the control? Explain briefly. 9