Physical quantity

Physical Quantity

An ammeter, a device used to measure electric current, which is a physical quantity.

A physical quantity is a property of a material or system that can be quantified by measurement. A physical quantity can be expressed as the product of a numerical value and a unit. Physical quantities are fundamental to the field of physics and are used to describe the laws of nature.

Types of Physical Quantities

Physical quantities can be broadly classified into two categories:

Fundamental Quantities

Fundamental quantities are those that are not defined in terms of other quantities. They form the basis for the measurement of other physical quantities. The International System of Units (SI) defines seven fundamental quantities:

• Length
• Mass
• Time
• Electric current
• Temperature
• Amount of substance
• Luminous intensity

Derived Quantities

Derived quantities are those that are defined in terms of the fundamental quantities. Examples include:

• Velocity (derived from length and time)
• Acceleration (derived from velocity and time)
• Force (derived from mass and acceleration)
• Energy (derived from force and distance)

Measurement of Physical Quantities

The measurement of physical quantities involves comparing the quantity to a standard unit. Instruments such as the ammeter (shown in the image) are used to measure specific physical quantities. The ammeter measures electric current, which is a fundamental physical quantity.

Units of Measurement

Units of measurement are standardized quantities used to express physical quantities. The SI units are the most widely used system of units. Each physical quantity has a corresponding SI unit:

• Length - metre (m)
• Mass - kilogram (kg)
• Time - second (s)
• Electric current - ampere (A)
• Temperature - kelvin (K)
• Amount of substance - mole (mol)
• Luminous intensity - candela (cd)

Dimensional Analysis

Dimensional analysis is a technique used to understand the relationships between different physical quantities by analyzing their dimensions. It is useful for checking the consistency of equations and converting units.

Related Pages

• Measurement
• SI base unit
• Dimensional analysis
• Physics