Date post: | 15-Apr-2017 |
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Education |
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• About different types of graphs,
• How to draw them when you are doing your practical work,
• How to interpret the different shapes.
Learning Objectives
You should learn :
Drawing a graphWhen should I
draw a line-graph…?
…and when should
I draw a bar-graph…?
…and when should I draw a histogram
or circle graph?
Drawing a graphLook at the table of your results:
If this column has• Many continuous ranges
of values,use a histogram:
• Continuous values,use a line-graph:
• Fixed items that are usually not numerical,Use a bar graph:
• Percentage of any kind,Use a circle graph
5 steps in drawing a graph1. Choose simple scales.For example:1 large square = 1 meter (1 m)or1 large square = 2 m, or 5 m, or 10 mBut never choose an awkward scale, like 1 square = 3 m or 7 mChoose a scale that will make your graph use most of the space available.
5 steps in drawing a graph1. Choose simple scales.Put the dependent variable on the ‘y-axis’
and the independent variable on the ‘x-axis’
5 steps in drawing a graph2a. Plot the points
neatly.To mark the points we usually use an X
xx
xx
xx
Re-check each one before your next step.
Usually you need 5 or more points for the graph.
5 steps in drawing a graph2b. Alternative plotting.•To mark the points we can also use a dot in a circle .
Re-check each one before your next step.
•Make sure the dot is very
small and the circle has a diameter no greater than
2mm
5 steps in drawing a graph3. If the points form a straight
line……draw the best straight line through them
xx
xx
xx
Check that it looks the best straight line.
‘line of best fit’
5 steps in drawing a graph4. If the points form a curve……draw a free-hand curve of best fit
Do not join the points like a ‘dot-to-dot’.
5 steps in drawing a graph5. If a point is not on the line……use your apparatus to check this measurement again
You should ignore anomalous points.
This is called an anomalous point. x
x
xx
xx
5 steps in drawing a graphIn summary:1. Choose good scales,
with the dependent variable on the y-axis
2. Plot the points carefully3. Draw a line of best fit
using a ruler for a straight line graph,4. or draw free-hand for a curved graph5. Check anomalous points.
A special case is when the straight line goes through the origin :
origin
In this case the two quantities are directly proportional.
Don’t forget to place both, the 0 for the x-axis and the 0 for the y-axis.
0 1 2 3 4 5 6 Time/days
Height/cm
543210
A curved graph, rising :
The dependent variable rises quickly at first and then more slowlyHere is an example:
Example : the volume of O2 produced in the catalase reaction against the time.
Volu
me
of O
2
/ml
Time/s
Eventually the reaction will stop producing O2 gas.
A curved graph, falling :
The dependent variable falls quickly at first
and then more slowlyHere is an example:
Example: The mass of starch left in the amylase reaction.
Mass of starch/g
Time/s
Starch Maltose
Amylase