Physical Quantity - Practice Questions & MCQ

• 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.   

Amount of physical quantity $(\mathrm{Q})=n u$

$$
\begin{aligned}
& n=\text { numerical value or magnitude } \\
& u=\text { unit }
\end{aligned}
$$

- For a given amount of physical quantity|
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 $=\frac{\text { density of object }}{\text { density of waterat } 4^{\circ} \mathrm{C}}$