Unit of Length - SI Unit and Other Common Units

Edited By Vishal kumar | Updated on Sep 24, 2024 06:40 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.

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Unit of Length - SI Unit and Other Common Units

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).

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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 or . Similarly, the minimum length that a vernier caliper can measure accurately is or . 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 m and the range of the observable universe extends up to a distance of m. 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.

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

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 = m.

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

1 angstrom = 1m.

1 micron = 1m = m.

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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)

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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 × m

2. 1 Angstrom = 1 Å = 1 × m

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

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

5. 1 parsec = 3.08 × 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:

Frequently Asked Questions (FAQs)

1. Which of the following is not the unit of length? (A) meter (B) centimeter (C) kilometer (D) Newton

Option (D) is not the unit of length .Newton is the unit of force.

2. What is length in physics?

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

3. Meter is the standard unit of?

Meter is the standard unit of length.

4. What is the standard unit of length?

The standard unit of length is meter (m).

5. What is the fundamental unit of length in the metric system?

The fundamental unit of length in the metric system or MKS system is meter (m).

6. Length is one of the fundamental quantities. Justify this statement.

The length of an object is measured in metres. One metre is equal to the length of path travelled by light in vacuum in time interval 1/299,792,458 of a second. Since the value is always the same, it is a fundamental quantity.

7. How can we measure the distance of a star which is nearly 50 light years away from us? Can we measure the distance from a star 150 light years away using the same method?

We can measure the distance of a star that is 50 light years away using the parallax method. The star will be observed from two different locations on earth and by measuring the distance between both the locations and angle subtended by the star on both positions, the star distance can be calculated. This method cannot be used to measure a star which is more than 100 light years as the accuracy of the result is not achieved. Thus, we cannot measure the star 150 light years away from us using the same method.