Conversion of one Physical Quantity into other

We work with measurement and analysis on a daily basis. Regardless of whether we are measuring someone’s height or weight, a number and unit will be used to determine the actual measurement.

To represent this measurement, we must first associate everything we’re measuring with an amount, and these numbers must be different for various types of measurements. Physical quantities are those that allow us to represent a measurable quantity in a way that everyone can understand. Prior to these physical quantities, life was ambiguous, and measurement could not be expressed accurately, resulting in a great deal of confusion.

Physical Quantity – Definition

A physical quantity is defined by either saying how it is measured or how it is derived from other measurements. 

For example, we describe distance and time by explaining how they are measured, but we define average speed by stating that it is determined as distance travelled divided by travel time.

Physical quantity measurements are stated in units, which are standardised values.

Happiness, pain, and other life events, on the other hand, are not physical quantities since they cannot be quantified.

To determine the magnitude of a physical quantity measurement is required, compare two identical physical quantities.

Note – The numerical values convey a considerably more in-depth comprehension of physical quantities and equations than the qualitative descriptions alone.

Example – The weight of a person is a physical quantity, that is expressed in units of Kg or Pound.

Categories of Physical Quantity

The physical Quantity is categorised into two parts

1. Fundamental Quantities

The Fundamental Quantity is a physical quantity that cannot be expressed in any other physical quantity. It provides a base for other quantities, also known as Derived Quantities. 

Fundamental Quantities in Physics includes length, mass, time, electric current, thermodynamic temperature, luminous Intensity and amount of substance.

2. Derived Quantities

Derived quantities are those quantities that cannot be specified in itself and must be subdivided into base quantities. It is expressed in terms of the fundamental quantity.

Derived quantities are calculated quantities based on two or more measurements. These are dependent quantities that cannot be measured directly. They are just calculated. 

Acceleration, volume, and force are some examples of Derived Quantity.

What is a Unit?

Units are measuring standards for physical quantities that require explicit definition in order to be useful. Standard units must be reproducible and widely accepted all over the world. As a result, each number must be followed with a unit, or else it will be meaningless. 

Although different systems of units have been evolved over time, the international system of units, or SI system, was created to minimize any misunderstanding. These units are connected to one another and can be transformed into one another; it would have been so difficult in order to express a quantity without such well-defined units.

For example – if you are calculating the weight of the vegetable bag and it is 5 kg, then if you say only 5 it is meaningless, but after 5 when you will add a unit as kg it will be meaningful.

Fundamental Unit

A fundamental unit is one that is independent of any other unit. These are the fundamental units that cannot be deduced from the others and are specified using an international system of units.

Some of the Fundamental Units are:

1. Meter – A meter is defined as the distance travelled by a ray of light in a vacuum for a time period of 1/299,792,458 of a second. It is represented as m and it is a fundamental unit of length.
2. Kilogram – Kilogram is represented as Kg, and it is the fundamental unit that is used for mass. One kilogram was initially defined as the mass of a platinum-iridium alloy cylinder kept in the International Bureau of Weights and Measures. It is now determined by the fixed value of Planck’s constant (h).
3. Ampere – 1 ampere equals 1 coulomb of charge per second. An ampere is a unit of measurement for the rate of electron flow or current in a conductor. It is represented by capital A.
4. Second – It is the fundamental unit of time that is represented by s. One second elapses during 9,192,631,770 cycles of radiation produced by the transition of two levels of the cesium 133 atom.
5. Kelvin – It is the fundamental unit of temperature, temperature is represented by k. One kelvin is defined as the temperature that is 1/273.16 of the thermodynamic temperature of the triple point of water.

Derived Unit

A derived unit is a unit of measurement in the International System of Units (SI) that is derived from one or more of the seven fundamental units.

Conversion

When the value of a physical quantity is provided in one system, the method of dimensional analysis can be used to determine its value in another system. T the measurement of a physical amount is determined by:

Q = nu is the formula for measuring a physical quantity.

If the unit of a physical quantity in a system is , and the numerical value is , then

In the other system, 

If the unit is and the magnitude is , then

From Eqs. (1) and (2),

If a,b,c are the dimensions of a physical quantity in mass, length, and time, then: 

As  and are the units of mass, length, and time in the two systems.

Then the outcome equation can be used to find the value of a physical quantity in the second or new system when its value in the first system is known.

Conclusion

There can be a lot of confusion among people when there is no specified unit that will be standardized. That’s why various systems were established to give a standard name to any physical quantity so that they can be used everywhere as a standard unit for measurement. However there are only 7 fundamental units and various units are derived from them. Although you can do conversion between two units too, that is explained in the paragraph above. Hope this article will help you.