Summary
Chapter 13 of the Class 8 Maths NCERT textbook, "Introduction to Graphs", teaches how to represent data visually through graphs, particularly line graphs that display data changing over time, and how to interpret and draw linear graphs to show relationships between dependent and independent variables.
- Why graph over tables — Graphs make numerical facts easier to grasp than tables, and line graphs in particular capture data that changes continuously over time, such as temperature or distance-time relationships.
- Plotting and reading graphs — Students plot points on a coordinate grid and join them into linear graphs, then read the graph back to estimate values between plotted points by following the grid lines.
- Variables and direct variation — Independent variables drive dependent ones, and when two quantities keep a constant relationship they are in direct variation — always producing a straight-line graph, as with deposits and simple interest.
Key points & formulas
- 01Graphs are visual representations of data that make numerical facts easier to understand than tables
- 02A line graph displays data that changes continuously over periods of time, with a horizontal axis (x-axis) and vertical axis (y-axis)
- 03A linear graph is an unbroken line formed by joining points plotted on a coordinate grid
- 04Independent variables affect dependent variables; for example, electricity used affects the bill amount
- 05Linear graphs can help estimate values between plotted points by following grid lines to locate unmeasured positions
- 06Direct variation occurs when two quantities maintain a constant relationship; the corresponding graph is always a straight line
- 07Real-world applications include temperature tracking, financial calculations, distance-time analysis, and performance comparisons
Frequently asked questions
01What is the purpose of using graphs instead of tables to show data?
Graphs provide a visual representation of data that can be understood quickly, easily, and clearly. They make it easy to identify trends, patterns, and comparisons that might be difficult to spot in a table. For example, a graph immediately shows whether a quantity is increasing, decreasing, or remaining constant over time.
02What is a line graph and when is it used?
A line graph displays data that changes continuously over periods of time. It consists of points plotted on a coordinate grid and connected by line segments. Line graphs are used for situations like tracking body temperature over hours, recording distance traveled over time, or showing sales figures across years.
03What are independent and dependent variables in a graph?
An independent variable is a quantity you control or that changes on its own, like quantity of electricity used or litres of petrol purchased. A dependent variable is one that changes as a result of the independent variable, like the amount of the electricity bill or the cost of petrol. On a graph, the independent variable is typically shown on the horizontal axis and the dependent variable on the vertical axis.
04What is a linear graph and what does it tell us?
A linear graph is a straight-line graph formed when two quantities are in direct variation—meaning they maintain a constant relationship. For example, if the cost of apples is 5 rupees each, the total cost increases proportionally with the number of apples. A linear graph passing through the origin indicates that when one quantity is zero, the other is also zero.
05Is the Class 8 Mathematics Chapter 13 Introduction to Graphs PDF free to download?
Yes, the NCERT Chapter 13 Introduction to Graphs textbook PDF is free to download. No sign-up or payment is required. You can access it directly on cbseprepmaster.com along with other NCERT Class 8 Mathematics chapters.
More chapters in Mathematics
Read Chapter 13 of Mathematics — the Class 8 Mathematics NCERT textbook (2026-27 edition) — online for free: the complete chapter as published by NCERT with every diagram, solved example and exercise, with step-by-step solutions, answers and revision notes. Open the NCERT PDF above, or browse all NCERT Class 8 textbooks.
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