Meaning of Conversion of Units
In physics, we usually need to convert units from one standard to another, such as mile to meter, hour to second, meter to an inch, feet to meter, kilogram to the gram, and so on. You'll need to know how to convert meter to the inch, a kilometer to a mile, and so on, such as 1m = 39.37in or 1km = 0.6214mi.
When the quantity expressed is not in our familiar format, such as when we want to convert units to SI units, unit conversions are required (in physics, we always convert units to SI units). We may not be familiar with the value of a physical quantity when expressed in a different unit format. Instead, you might want to add the values in a calculation that involves another unit. In this article, we have provided different conversion units for measuring different parameters. Let us start by understanding the conversion of units in the coming section.
Conversion of Units
The primary focus of this chapter is to tackle the conversion of units of measurement of various quantities. However, before we start, it is essential to understand fundamental and derived physical quantities and their units.
To learn how to convert units of physical quantities, it is necessary to be aware of the terms–dimensional formula and dimension equation. First, check these details about fundamental and derived quantities.
Fundamental Quantities and Derived Quantities
All measurable physical quantities can be primarily classified into two types, which are –
Fundamental Quantities
A small group of physical quantities are considered as fundamental quantities or primary quantities which are used to derive other physical quantities.
For Example: Mass, time, length, electric current, the luminous intensity of light, temperature, amount of substance are all fundamental quantities.
Derived Quantities
Also referred to as secondary quantities, derived quantities are formed from primary or fundamental quantities.
For Example: By dividing distance by time, we can calculate the speed of an object. Hence, speed is a prime example of a derived quantity.
Additionally, if we multiply the breadth, length and height of an object, we get to derive the volume. So volume is also another example of a derived quantity.
Fundamental and Derived Units
Units selected for primary physical quantities are known as fundamental units. Meanwhile, those units which are formed with the help of fundamental units are termed derived units.
For Example: Speed is a derived quantity whose unit is determined as distance/time, i.e. metre/second. Here, you can notice that metre and second are fundamental units while the unit of speed, i.e, metre/second, is a derived unit.
A Complete Unit Conversion Table
To solve numerical problems in the case of unit conversion questions in physics, consulting a tabulated form of unit conversions is highly important, especially for beginners.
Several tables containing the unit conversion formulas are given below, which sum up almost every essential physical quantity. Each table contains various units and their conversions of a specific physical quantity, fundamental or derived. Let us now learn unit conversion with the help of the unit conversion table.
Basic Unit Conversion Table – Length
Unit Conversion List – Mass
Units of Measurement Conversion Table – Volume
Units and Conversions – Time
Unit Conversion Table – Energy
Unit Conversion Table- Power
Numerical Problems from Unit Conversion Tables
Numerical problems with the conversion of units in physics are quite common in exams. For example, the following question is frequently asked –
1. State the Relationship Between Dyne and Newton?
Ans: As we know, dyne and Newton are units of force. The dimensional formula of force is [MLT-2].
Hence, 1 Newton = 1 x kg x m x s-2 = 1 x 103 g x 103cm x s-2 = 1 x 106 g x cm x s-2
So, Newton = 106 dyne.
At Vedantu, we hope that this discussion on the Conversion of Units will help you attain high marks in the upcoming physics exams. Moreover, make sure to download our Vedantu app to access study materials and online classes easily.
FAQs on Conversion of Units
1. What is meant by conversion of units in physics?
Conversion of units in physics refers to the process of expressing a physical quantity in different measurement systems or units, such as converting distance from metres to kilometres or time from seconds to minutes. This is essential for calculations, consistency, and accuracy in scientific communication as per CBSE standards.
2. Why is it important to use SI units in all scientific calculations?
Using SI units ensures uniformity and avoids confusion when performing calculations or comparing results globally. It helps prevent errors due to mixed units, which is crucial for exams and scientific understanding in the 2025–26 CBSE Physics Syllabus.
3. How can you convert derived units, such as speed, from one system to another?
To convert derived units like speed, convert each base unit separately using the conversion factor. For example, to convert speed from km/h to m/s, multiply the value by 1000/3600 (since 1 km = 1000 m and 1 hour = 3600 seconds).
4. What is a unit conversion factor and how is it applied?
A unit conversion factor is a numerical value used to convert one unit to another without altering the actual quantity. It is applied by multiplying or dividing the original value by this factor. For example, to convert 2 inches to centimetres, multiply by 2.54 (as 1 inch = 2.54 cm).
5. What are the fundamental and derived units, and how do they relate in unit conversions?
Fundamental units are basic physical measurements like metre (length), kilogram (mass), and second (time). Derived units are combinations of these, such as newton (force) or joule (energy). In unit conversions, derived units require conversion of all constituent fundamental units.
6. Can using incorrect units affect the outcome of physics numericals?
Yes, using incorrect units leads to wrong answers and may result in loss of marks. Physics numericals must be solved using the correct units throughout, as per the latest CBSE exam pattern, to ensure full credit and conceptual clarity.
7. How do you approach solving numerical problems that involve multiple unit conversions?
When multiple unit conversions are involved,
- List all physical quantities and their given units.
- Convert each value to SI units using appropriate conversion factors.
- Proceed with calculations only after all quantities are in compatible units.
- Express the final answer with correct units as per CBSE guidelines.
8. What conceptual mistakes should students avoid in unit conversions during CBSE board exams?
Common mistakes include forgetting to convert all units to SI, ignoring conversion factors in derived units, and mismatching units in equations. Always check unit consistency before and after calculations to avoid these pitfalls.
9. Explain with an example: How is force converted from dyne to newton?
The SI unit of force is newton (N), and in the CGS system, it is dyne.
- 1 newton = 105 dyne
- To convert 300,000 dyne to newton: 300,000 dyne ÷ 100,000 = 3 N
10. How can mastering unit conversions help in competitive exams besides the CBSE board?
Proficiency in unit conversions saves time during calculations, reduces mistakes, and boosts scores not just in CBSE board exams but also in entrance tests like JEE and NEET, where conceptual clarity and speed are essential.
