Vector And Scalar Quantities

In mathematics and physics, we have physical quantities which can be categorized in two ways, namely

• Scalar Quantity
• Vector Quantity

Scalar Quantity Definition

The physical quantities which have only magnitude are known as scalar quantities. It is fully described by a magnitude or a numerical value. Scalar quantity does not have directions. In other terms, a scalar is a measure of quantity. For example, if I say that the height of a tower is 15 meters, then the height of the tower is a scalar quantity as it needs only the magnitude of height to define itself. Let’s take another example, suppose the time taken to complete a piece of work is 3 hours, then in this case also to describe time just need the magnitude i.e. 3 hours.

Scalar Quantity Examples

Other examples of scalar quantities are mass, speed, distance, time, energy, density, volume, temperature, distance, work and so on.

Vector Quantity Definition

The physical quantities for which both magnitude and direction are defined distinctly are known as vector quantities. For example, a boy is riding a bike with a velocity of 30 km/hr in a north-east direction. Then, as we see for defining the velocity, we need two things, i.e. the magnitude of the velocity and its direction. Therefore, it represents a vector quantity.

Vector Quantity Examples

Other examples of vector quantities are displacement, acceleration, force, momentum, weight, the velocity of light, a gravitational field, current, and so on.

Vector Representation

Let us have a look at the line segment drawn below. A vector quantity always has a starting point and an endpoint. The two endpoints of the given line segment are distinguishable as and. It represents a directed line segment

The directed line segment with an initial point  A and terminal point B  is symbolically denoted as  AB  in bold.

\(\begin{array}{l}\text{Also, it can be represented as} \ \overrightarrow{AB}\end{array} \)

The length a of the vector represents its magnitude which is denoted by |AB|. Instead of using double letter notation we can use a single letter notation to represent a vector as a, b, c and it denotes their magnitudes. As it is difficult to write letters in bold we use a bar above the letters to represent vectors as ā.

Therefore,

\(\begin{array}{l}\text{If} \ \overrightarrow{AB} = a,\ \text{then} |\overrightarrow{AB}| = a, \\ \text{where} \ |\overrightarrow{AB}|\ \text{indicates the magnitude of a vector.}\end{array} \)

Also, the magnitude is called the modulus.

Characteristics of Vectors

The characteristics of the vectors are as follows:

• Vectors possess magnitude as well as the direction
• It does not obey the ordinary law of algebra
• Either the magnitude or direction change or both change

Scalar and Vector Quantity Example

Question: 

Find out the scalar and vector quantity from the given list.

Force, Speed,  Electric field, Angular Momentum, Magnetic Moment, Temperature, Linear Momentum, Average Velocity.

Solution:

From the given list,

• Scalar Quantities – Speed, Temperature.
• Vector Quantities – Force, Electric field, Angular Momentum, Magnetic Moment, Linear Momentum, Average Velocity.

&

Win