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Graphs - Lesson Summary


A graph is a pictorial representation of two sets of numerical data. The saying, "A picture is worth a thousand words," is exactly true in the case of graphs. The data represented in a graph is self explanatory.

Types of Graphs

There are three types of graphs: Bar graphs, pie charts and line graphs.
���� •� A bar graph is also known as a histogram. A bar graph consists of horizontal or vertical bars that show the values of one quantity against another. These are useful when there is a numerical comparison. For example, it compares the performance of a team across matches in a series.
���� •� A pie chart is a circular graph used to represent relative percentages or shares of a total. �It looks like a pie cut into several slices, and hence the name pie chart. Each slice is called a sector of the chart. A pie chart is used to showcase a whole quantity and the whole quantity is broken into parts.
���� •� A line that joins dots plotted on a graph paper is called a line graph. It is used to show the variation of a quantity with respect to another. A line graph represents two pieces of information that are usually related. It is useful when comparisons are needed.

Uses of Graphs

Graphs are used for better understanding of numerical data. They are useful in establishing a relation between two quantities measured in an experiment. They are also useful in comparing different sets of data. For example, using graphs, the performance of two batsmen can be compared. Also, in population studies, these graphs are used to compare the birth and the death rate, and other kinds of data.

Motion of objects can be presented in pictorial form by their distance-time (d-t) graphs. From the shape of the d-t graph one can say what type of motion is executed by a body. For a body in uniform motion, the d-t graph is a straight line making an angle with the horizontal axis. For a body at rest the d-t graph is a straight line parallel to the horizontal axis. For a body in non-uniform motion, the d-t graph is not a straight line and it can be of any shape.

Plotting a Graph

To plot a graph on a graph sheet:
���� •� Take a graph paper.
���� •� At the centre of the paper, draw two lines perpendicular to each other.
���� •� Mark the point of intersection of the lines as ‘O.’
���� •� The horizontal line is called the X-axis, while the vertical line is called the Y-axis. The point of intersection of the two axes is called the origin, "O".
���� •� Take one quantity along the X-axis and the other along the Y-axis, after choosing suitable scales for both. For every value along one axis, mark a point matching the related value on the other axis.
���� •� Join the points, and your graph is ready.

While choosing the scale for the graph, it is important to keep in mind the following points: �the difference between the maximum and the minimum values of each quantity,�the intermediate values of each quantity, so that with the scale chosen it is convenient to mark the values on the graph, and to utilise the maximum part of the graph paper.


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