NCERT Class 11 Physics Physics Part-I: Chapter 3 — 1 INTRODUCTION
This chapter introduces the concepts of vectors necessary to describe motion in two or three dimensions, building upon the one-dimensional concepts of position, displacement, velocity, and acceleration from the previous chapter. It distinguishes between scalar quantities (magnitude only, like mass and temperature) and vector quantities (magnitude and direction, like displacement and force), explaining how they are represented and combined. The chapter details position and displacement vectors, defining them geometrically and illustrating their independence from the actual path taken. It also introduces the notation for vectors and the condition for vector equality. The text sets the stage for discussing motion in a plane, including projectile motion and uniform circular motion, which are crucial for understanding various physical phenomena.
Quick info
| Board | CBSE / NCERT |
|---|---|
| Class | Class 11 |
| Subject | Physics |
| Book | Physics Part-I |
| Chapter | Chapter 3 — 1 INTRODUCTION |
| Language | English |
| PDF type | NCERT Textbook |
| Session | CBSE 2026 |
| Reading time | 6 minutes |
| Word count | 1111 |
Learning outcomes
- Distinguish between scalar and vector quantities.
- Understand the representation and properties of position and displacement vectors.
- Define and identify vector quantities like velocity, acceleration, and force.
- Grasp the concept of vector equality.
- Prepare for the study of motion in two and three dimensions.
Vocabulary
| Word | Meaning |
|---|---|
| Scalar | A quantity with magnitude only. |
| Vector | A quantity with both magnitude and direction. |
| Position vector | A vector representing the location of an object from an origin. |
| Displacement vector | A vector representing the change in position of an object. |
| Magnitude | The size or length of a vector. |
| Direction | The orientation of a vector in space. |
| Triangle law of addition | A rule for adding vectors graphically. |
| Parallelogram law of addition | An equivalent rule for adding vectors graphically. |
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Practice questions
- What is the main difference between a scalar and a vector quantity? Answer: A scalar quantity has only magnitude, while a vector quantity has both magnitude and direction.
- Give two examples of scalar quantities and two examples of vector quantities. Answer: Scalar examples: mass, temperature. Vector examples: displacement, force.
- What does a displacement vector represent? Answer: A displacement vector represents the straight-line change in position from an initial point to a final point, irrespective of the path taken.
- Under what conditions are two vectors considered equal? Answer: Two vectors are equal if they have the same magnitude and the same direction.
Practice MCQs
Q1. Which of the following is a scalar quantity?
Explanation: Mass is a scalar quantity as it only has magnitude. Velocity, acceleration, and force are vector quantities as they have both magnitude and direction.
Q2. A vector quantity must have:
Explanation: Vector quantities are defined by having both a magnitude (size) and a direction.
Q3. The displacement vector is independent of:
Explanation: The displacement vector connects the initial and final positions directly and does not depend on the path followed between them.
Q4. Which of the following obeys the triangle law of addition?
Explanation: Vector quantities are defined by their adherence to vector addition laws like the triangle law or parallelogram law.
Q5. If a vector is represented by an arrow, the length of the arrow indicates its:
Explanation: The length of the arrow used to represent a vector is proportional to its magnitude.
Frequently asked questions
What is the primary purpose of introducing vectors in Chapter 3 of NCERT Physics Part-I?
Vectors are introduced to describe motion in two or three dimensions, where simple + and - signs are insufficient to represent direction.
What is the key difference between a scalar and a vector?
A scalar has only magnitude, while a vector has both magnitude and direction.
Can you give examples of scalar and vector quantities from everyday life?
Scalar examples include temperature, mass, and speed. Vector examples include displacement, velocity, and force.
How is a displacement vector different from the actual path taken by an object?
The displacement vector is a straight line from the initial to the final position, regardless of the path followed, while the path length is the total distance covered.
What does it mean for two vectors to be equal?
Two vectors are equal if they possess the same magnitude and point in the same direction.
What are the main topics covered in the 'Motion in a Plane' chapter?
The chapter covers scalars and vectors, their addition/subtraction, motion in a plane, projectile motion, and uniform circular motion.
Related resources
Important topics
Topics covered
NCERT Class 11 Physics — Physics Part-I — Chapter 3 — 1 INTRODUCTION. Verified by NCERT Help Editorial Team. Reviewed on 29 Jul 2026. Last updated 10 Aug 2026.