Unit of Distance - SI Unit And CGS Unit, FAQs
The unit of distance in physics is used to measure the length between two points accurately. Distance is a fundamental physical quantity and is expressed in specific units depending on the measurement system. In the International System of Units (SI), the standard unit of distance is the metre (m). Smaller units like millimetre (mm) and centimetre (cm), and larger units like kilometre (km), are commonly used for practical measurements. In scientific studies, systems such as CGS and MKS define standard units for consistency in calculations. For extremely large distances in astronomy, the light-year is used. Understanding units of distance and their conversions is essential for Class 11 Physics, board exams, and competitive exams like JEE and NEET.
This Story also Contains
- Unit of Distance in Physics:
- SI Unit of Distance:
- Distance Conversion
Unit of Distance in Physics:
Distance is the measurement of length between two points and the numerical value of distance calculated in a specific unit and these units are known as unit of distance. For example, when we say the distance between Delhi and Mumbai is 1412Km then Km represents some unit and this is the unit of distance measured between two places. There are many units of distance in physics and used according to the need.
SI Unit of Distance:
The term SI stands for Standard system of units and there are fundamental units that are defined in SI system and are used by all countries to avoid conflict while doing physical experiments and calculations. The SI unit of distance is known as the meter. The SI unit of distance meter is denoted by the letter ‘m’.
Also read -
- NCERT Solutions for Class 11 Physics
- NCERT Solutions for Class 12 Physics
- NCERT Solutions for All Subjects
Smallest Unit of Length
The smallest measurable unit of length commonly used in daily life is the millimetre (mm).
$
1 \mathrm{~mm}=10^{-3} \mathrm{~m}
$
In the microscopic world, especially in nuclear physics, extremely small distances are measured in Fermi metre (fm).
$
1 \mathrm{fm}=10^{-15} \mathrm{~m}
$
The Fermi metre is used to measure the size of atomic nuclei.
Largest Unit of Length
The commonly used largest unit of length in everyday measurement is the kilometre (km).
$
1 \mathrm{~km}=1000 \mathrm{~m}
$
It is used to measure long distances such as between cities.
CGS Unit of Distance
The CGS system (Centimetre-Gram-Second) uses centimetre (cm) as the unit of length.
$
1 \mathrm{~cm}=0.01 \mathrm{~m}
$
MKS Unit of Length
The MKS system (Metre-Kilogram-Second) uses metre (m) as the unit of length.
The metre is also the SI unit of length.
Unit of Distance in Astronomy
In astronomy, extremely large distances are measured in Light-Year (ly).
A light-year is the distance travelled by light in one year in vacuum.
$
1 \text { Light-Year }=9.46 \times 10^{15} \mathrm{~m}
$
This unit is used to measure distances between stars and galaxies.
Also Read:
Distance Conversion
Here are the standard conversion values between common units of length:
| Unit | mm | cm | m | km |
| 1 millimetre (mm) | 1 | 0.1 | 0.001 | 0.000001 |
| 1 centimetre (cm) | 10 | 1 | 0.01 | 0.00001 |
| 1 metre (m) | 1000 | 100 | 1 | 0.001 |
| 1 kilometre (km) | 1,000,000 | 100,000 | 1000 | 1 |
| 1 inch (in) | 25.4 | 2.54 | 0.0254 | 0.0000254 |
Important Points
-
1 m = 100 cm
-
1 km = 1000 m
-
1 cm = 10 mm
-
1 inch = 2.54 cm
Also check-
- NCERT Exemplar Class 11th Physics Solutions
- NCERT Exemplar Class 12th Physics Solutions
- NCERT Exemplar Solutions for All Subjects
NCERT Physics Notes:
Frequently Asked Questions (FAQs)
The metre is the SI unit of distance while the centimetre is the unit of distance in CGS systems and the Light year is the unit of distance in astronomy but the Year is the unit of time. Hence, (C) Year is not a unit of distance.
In physics, Parsec is a unit of distance and it is defined as when the radius of our planet earth makes an angle of a second of an arc, then the distance at which this angle subtended by earth is referred as a parsec. Mathematically 1Parsec=3.26Light years. Hence, (D) Distance parsec is a unit of measurement of Distance.
1m=0.001Km
1Km=100000cm
