Transcript 1.1 Mole Concept & Avogadro’s Constant

11.3 Graphical Techniques
Assessment statement
Teacher’s notes
11.3.1
Sketch graphs to represent dependences and interpret
graph behaviour.
Students should be able to give a
qualitative physical interpretation
of a particular graph, for example,
the variables are proportional or
inversely proportional.
11.3.2
Construct graphs from experimental data.
This involves the choice of axes
and scale, and the plotting of
points.
11.3.3
Draw best-fit lines through data points on a graph.
These can be curves or straight
lines.
11.3.4
Determine the values of physical quantities from graphs.
Include measuring and
interpreting the slope (gradient),
and stating the units for these
quantities.
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11.3 Graphical Techniques
Graphing is used extensively in Science and is a very
powerful method to show the relationship between
two variables.
Additionally, it is often the best method of
presenting and analyzing data. It also gives an
indication of the reliability of the measurements.
The relationship is between an independent
variable (the cause) (on the horizontal axis) and a
dependent variable(the effect) (on the vertical axis).
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11.3 Graphical Techniques
The relationship is between an independent
variable and a dependant variable.
•The independent variable is the variable that the
experiment intentionally changes.
•The dependent variable is then measured to find if
it changes, to determine if it is dependent on the
independent variable.
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11.3 Graphical Techniques
With a few notable exceptions, a graph is made
with the independent variable plotted on the x-axis,
and the dependent variable on the y-axis.
The shape of the graph will give us a strong
indication of the relationship between the
variables.
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11.3 Graphical Techniques
When data has been plotted and establishing a best
fit line, the line can be “extended” beyond the
recorded data. Using this technique of estimating
data not directly measured is known as
Extrapolation.
When data has been plotted and establishing a best
fit line, it can be assumed that the trend between
two data points is consistent with the present data.
This is called Interpolation.
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11.3 Graphical Techniques
Pointers:
•Give your graph a title (helps to put the reader into
the right context)
•Label both axes with quantities and units (so the
reader understands what you’re talking about)
•Use the space effectively (don’t plot only using a
small corner if your graph covers the entire page)
•Use sensible linear scales (make sure there are no
uneven “jumps” in the units along an axis)
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11.3 Graphical Techniques
Pointers (cont.):
•Plot all the points correctly (your data is your data, you get
what you get!)
•A Best Fit line should be drawn smoothly and clearly. (It does
NOT need to go through all the points, but show an overall
trend of the points).
•If your Best Fit line passes through the origin shows the
dependent and independent variables are proportional.
Don’t forget the equation for a straight line: y = mx + b
y = dependent variable,
m = gradient/slope,
x = independent variable
b= intercept on the vertical (y) axis).
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