Physical Quantity

Solve by difficulty

Which of the following statements is true regarding physical quantities?

Physical quantities can be defined only by their units.

Physical quantities can be defined only by their magnitudes.

Physical quantities can be defined by both their units and magnitudes.

Physical quantities cannot be defined.

Concepts Covered - 1

Physical quantity

A quantity that can be measured and expressed in the form of laws is called a Physical quantity.
A physical quantity is expressed completely by its magnitude and unit.
One physical quantity can be represented in terms of one or more units.

$\text{Amount of physical quantity(Q)}=nu$

$n= numerical \: value \ \ or \ \ magnitude$

$u= unit$

nu =constant

So $n_{1}u_{1}=n_{2}u_{2}= constant$

So $n\alpha \frac{1}{u}$

So larger the unit smaller will be the magnitude.

Types of the physical quantity

1) Scalar Quantity

The quantities having magnitude only are known as a scalar quantity.
It does not specify the direction.
Scalar quantity can be added or subtracted by the laws of addition or subtraction.
Examples-Distance, time, work, energy, etc

2) Vector Quantity

The quantities having both directions as well as magnitude are known as vector quantities.
It has a specific direction.
Vector quantity can be added and subtracted according to vector laws of addition.
Examples - Displacement, force, velocity, acceleration, momentum, etc.

3) Tensor Quantity

Scalar and vector are special cases of a tensor.

Tensors are represented in the multi-dimensional array, i.e, in different directions, tensors will have different magnitudes.
If a tensor has only magnitude and no direction, it is called scalar (a tensor of rank zero).
If a tensor has magnitude and one direction, it is called a vector (a tensor of rank one).
Examples- Stress, The moment of inertia, coefficient of viscosity.

4) Ratio Quantity

When a physical quantity is the ratio of two similar quantities.

$eg.\ Relative \: density = \frac{density\: of \: object}{density\: of\: water at\ 4^{\circ}c}$