Class 11 NCERT PHYSICS • Chapter 3: Motion in a Plane • Question 2

QUESTION 2

Pick out the two scalar quantities in the following list :

force, angular momentum, work, current, linear momentum, electric field, average velocity, magnetic moment, relative velocity

SOLUTION

We need to identify the two scalar quantities from the provided list of physical parameters.

Concept: Scalar Quantity

A scalar quantity is a physical quantity that is completely described by its magnitude alone. In contrast, a vector quantity requires both magnitude and direction and must obey the laws of vector addition.

Given:

The list of quantities is: force, angular momentum, work, current, linear momentum, electric field, average velocity, magnetic moment, relative velocity.

Solving:

Force, angular momentum, linear momentum, electric field, average velocity, magnetic moment, and relative velocity are all vector quantities because they have specific directions and their addition follows vector rules (e.g., the parallelogram law).
Work ( $W$ ) is defined as the dot product of the force vector $\vec{F}$ and the displacement vector $\vec{s}$ :

W = \vec{F} \cdot \vec{s}

The result of a dot product between two vectors is always a scalar. Therefore, work is a scalar quantity.

Current ( $I$ ) has a direction (the direction of flow of positive charge), but it does not follow the laws of vector addition. For instance, at a circuit junction, the total current is the simple algebraic sum of the entering currents, regardless of the angles between the wires. Thus, current is treated as a scalar quantity.

Answer

\text{Work and Current}