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Unit of Length - SI Unit and Other Common Units

Unit of Length - SI Unit and Other Common Units

Vishal kumarUpdated on 02 Jul 2025, 05:01 PM IST

Here, in this article we are going to discuss SI unit of length, unit of length, standard unit of length, what the standard unit of length is, what is the SI unit for length, what the SI unit of length is, what is the standard unit of length, what SI unit of length is, what is the unit of length, basic unit of length, the basic unit of length is, what is the basic unit for length, all units of length, which unit is not for length, name the SI unit of length, What SI unit of length is called, define length in physics, what the standard unit of length is called, meter is the standard unit of, fundamental unit of length in the metric system etc.

Unit of Length - SI Unit and Other Common Units
Unit of Length

SI unit of length

The SI unit of length is meter (m).

Define length in physics

We define length in physics as the length of the path travelled by light in a vacuum in 1⁄299792458 seconds.

What is the standard unit of length?

The standard unit of length is meter (m).

CGS unit of length

The CGS unit of length is centimeter (cm).

MKS unit of length

The MKS unit of length is meter (m).

Also read -

Standard unit of length

There are several ways to measure distance and the device needed to make the measurement depends on the range of length to be measured and requirement of the level of accuracy. Now, let us take an example of a meter scale. The divisions on the scale are made at a separation of 1mm. Hence, the minimum distance it can measure accurately is 1641202937228or 1641202936324. Similarly, the minimum length that a vernier caliper can measure accurately is 1641202938663or 1641202937795. Now let us compare the meter scale used by a tailor to measure the cloth. A tailor uses a measuring tape to measure the dimensions of the body. So, we conclude that the choice of the measuring instrument depends on what we actually want to measure. For example, a vernier caliper is suitable to measure the diameter of a rod or small ball etc.

Range of Length

The size of the proton is of the order of 1641202936887m and the range of the observable universe extends up to a distance of 1641202936714m. We can see that in physics there is a wide range of lengths. Apart from the standard SI units we often require different units to be used in different contexts for convenience. Let us know more about these units.

Astronomical Unit (AU): The average distance between the Earth and the Sun is called 1 AU.

1641202939497m.

Light Year (ly): One light year is the distance travelled by light in one year with a speed of 1641202935812m/s.

1641202939648m.

Parallactic second (parsec):- One parsec is the distance at which the average radius of Earth’s orbit subtends an angle of 1 arc second.

1 parsec = 1641202936130m.

1 fermi (f) = 1 f = 1641202937955m. It is used to describe the radius of the nucleus.

1 angstrom = 11641202937061m.

1 micron = 11641202937607m = 1641202938495m.

Related Topics Link,

All units of length

Some other units of length are:-

1. kilometer (km)

2. Hectometer (hm)

3. Decameter (dcm)

4. Decimeter (dm)

5. Nanometer (nm)

6. millimeter (mm)

Also Read:

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Other Non-SI Length Units

1. Foot

2. Yard

3. Mile

4. Inch

Special units of length:

1. 1 fermi = 1 f = 1 × 1641202938118m

2. 1 Angstrom = 1 Å = 1 × 1641202936506 m

3. 1 astronomical unit = 1 AU = 1.496 × 1641202938274 m. It is the average distance of the sun from the earth.

4. 1 light year = 1 ly = 9.46 × 1641202938814 m. It is the distance travelled by light in one year, with a velocity of 3 × 1641202937388 m/s.

5. 1 parsec = 3.08 × 1641202939000 m. It is the distance at which the average radius of earth’s orbit subtends an angle of one arc second.

Also check-

NCERT Physics Notes:

Commonly Asked Questions

Q: What is the SI unit of length and why was it chosen?
A:
The SI unit of length is the meter (m). It was chosen because it's based on a fundamental constant of nature - the speed of light in vacuum. One meter is defined as the distance light travels in 1/299,792,458 of a second. This definition provides a universal standard that can be reproduced anywhere in the world with high precision.
Q: How does the definition of a meter relate to the speed of light?
A:
The meter is defined in terms of the speed of light in vacuum. Specifically, one meter is the distance light travels in 1/299,792,458 of a second. This definition links the unit of length directly to a fundamental constant of nature, ensuring its universality and reproducibility.
Q: Why don't we use everyday objects to define units of length anymore?
A:
Everyday objects are not reliable for precise measurements because they can change over time due to factors like temperature, humidity, and wear. For example, the meter was once defined by a metal bar, but this could expand or contract slightly with temperature changes. Using fundamental constants of nature, like the speed of light, provides a more stable and universally reproducible standard.
Q: How has the definition of the meter changed over time?
A:
The definition of the meter has evolved to become more precise and universal:
Q: What's the difference between a meter and a metre?
A:
There is no difference between a meter and a metre. "Meter" is the American English spelling, while "metre" is the British English spelling. Both refer to the same SI unit of length.

Frequently Asked Questions (FAQs)

Q: What are some common misconceptions about units of length in everyday life?
A:
Common misconceptions about units of length include:
Q: Why is the speed of light in vacuum considered a universal constant, and how does this affect our definition of length?
A:
The speed of light in vacuum is considered a universal constant because:
Q: How do quantum mechanics and string theory challenge our classical notion of length?
A:
Quantum mechanics and string theory challenge classical notions of length:
Q: What is dimensional analysis and how does it relate to units of length?
A:
Dimensional analysis is a method for analyzing the relationships between different physical quantities by identifying their fundamental dimensions. For length:
Q: How do we ensure that length measurements are consistent across different laboratories worldwide?
A:
Consistency in length measurements across laboratories is ensured through:
Q: What's the difference between a light-year and a parsec?
A:
Both light-years and parsecs are units used to measure astronomical distances:
Q: Why do we still use non-SI units like feet and inches in some countries?
A:
Some countries, like the United States, still use non-SI units due to:
Q: Why don't we use the wavelength of light to define the meter anymore?
A:
The meter was previously defined using the wavelength of light emitted by krypton-86 atoms. However, this definition was replaced because:
Q: How does the angstrom (Å) relate to SI units of length?
A:
The angstrom (Å) is a non-SI unit of length equal to 10^-10 meters or 0.1 nanometers. While not an official SI unit, it's still commonly used in some scientific fields, particularly for describing atomic-scale lengths, such as atomic radii or wavelengths of light. To convert:
Q: Why do scientists prefer to use SI units over other systems?
A:
Scientists prefer SI units because:
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