Solving Problems in Science
International Junior
Science Olympiad (IJSO)
Dr. Yu-San Cheung
yscheung@cuhk.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
2
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:
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 significant digits in your answer.
a. 7.2 mm x 1.56 mm =
b. 99.5 cm2 x 0.0084 cm =
c.
63.6 g/ 2.7 cm3 =
d. 288 g/16.9 cm3=
e. 0.001 g + 5.3 g + 162 g =
f.
32.58 cm3 – 5.2 cm3 =
5
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
8
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.
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