Use of Graphs: You may find it more appropriate to use graphs to present your results. You may refer to Box that tells about the procedure for plotting a graph. Graphs are particularly useful in showing the relationship between quantities rather than the actual quantities themselves. As an example, refer back to Figure which shows the relationship between temperature and time in the experiment to determine the freezing point of octadecanoic acid. This is a linear or straight line graph.
Box : Procedure for Plotting a Simple Graph.
In case you have any difficulty with elementary graphs and graph plotting, we have included some information to help you, although this material does not require learning for this unit.
When plotting graphs, use a sharp, fine pencil -grade HB or H. Do not use ink or felt tipped pens on your graph, and ensure that you place your graph paper on a hard flat surface.
Imagine that you have a table of figures connecting two variables and you want to express them as a graph. Follow this procedure as an easy guide.
1. Count the squares on the graph paper along the two adjacent sides. Note the two ranges of values of the variables to be plotted. The range is obtained from the maximum minus the minimum values.
2. Fit two ranges to the numbers of squares by choosing a scale for each variable. Le., work out how much of each variable there will be to each square. This should be as simple a value as possible, e.g., 0.1, 100 or some round number. Your scale should be such that you use up more than half the graph side.
3, Draw two lines (the axes) at right angles on the graph paper lines, near the sides. If possible, your lines should be ten small squares in from both sides and, for preassurance, include the values zero for each axis. The "co-ordinates" of this point are 0, O - the. First value is the horizontal value, preferably the measurement you alter.
4. Every point in the rectangle of the graph represents a possible pair of values (or set of co-ordinates). You have to mark the points representing each pair of values - horizontally from 0,O for the measurement that was altered and then vertically up to the measurement that resulted. Use either dots, or crosses, or circles to mark the point.
5. Draw the best single line you can through the points. If you think or know it should be a straight line but can't see where to draw it, try this:
a) Using a transparent straight edge, draw, faintly the most and least steep lines which seem satisfactory.
b) Then bisect the angle between the lines.
c) Draw this line in as your final line or curve.
6. The slope of the line can then be measured.
7. Label the axes of the graph and write your name and the date on the graph paper.