Content Curator
Unit of Length: Length is defined as the measurement of something from one end to the other. The SI unit of length is m, but there are many other units of length in other systems of measurement. Let us look at the various units of length that are used around the world.
Length
Length is the measurement of something from one end to the other. In other words, the length defines how long something is. It is defined as a quantity with dimension distance in the International System of Quantities.
The length of the path travelled by light in a vacuum within 1/299792458 seconds.
Units and Measurements Video Lecture
Unit
Any physical amount is measured by comparing it to a basic, arbitrarily chosen and internationally accepted reference standard known as a unit.
Different systems of units for measurement
- CGS system include centimetre, gram, and second
- FPS system include foot, pound, and second
- MKS system include metre, kilogram, and second
The Système Internationale' Unites (French for International System of Units), abbreviated as SI, is the international measurement system which is currently in use. The SI was established and recommended by the General Conference on Weights and Measures in 1971 for international use in scientific, technical, industrial, and commercial activities, with a consistent scheme of symbols, units, and abbreviations.
Unit of Length
The metre is the base unit for length in the International System of Units (SI). It is abbreviated as m.
This is possible when the length is given in appropriate units, such as 2 metres or 200 centimetres for a table, 15 metres for a string, and so on.
Other Units of Length
| 10 millimeters (mm) | 1 centimeter (cm) |
| 10 centimeters | 1 decimeter (d) |
| 10 decimeters | 1 meter (m) |
| 10 meters | 1 decameter (da) |
| 10 decameter | 1 hectometer (h) |
| 10 hectometers | 1 kilometers (km) |
Conversion of Units of Length
| Units | Conversion |
|---|---|
| Km to Cm | 1 km = 100000 cm |
| Km to M | 1 km = 1000m |
| Cm to m | 1 cm = 0.01m |
| M to mm | 1 m = 1000 mm |
| Cm to mm | 1cm = 10 mm |
Scientific Units of Length
Astronomical Unit: The mean distance between the Earth and the Sun is measured in astronomical units. It is used to calculate orbits and trajectories throughout the Solar System.
1 UA = 149,597,871 km
Light Year: The distance travelled by light in one average solar year is measured in light-years. It is used to measure extraordinarily long distances in astronomy.
1 light-year = 9,461,000,000,000 km
Parsec: A parsec is an astronomical unit of measurement that equals the distance between the earth and an astronomical object with a one-second parallax angle.
1 parsec = 30,857,000,000,000 km
Things to Remember Based on Unit of Length
- Length is the measurement of something from one end to the other.
- CGS system- centimetre, gram, and second
- FPS system- foot, pound, and second
- MKS system- metre, kilogram, and second
- Metre is the SI unit for length. It is abbreviated as m.
- The mean distance between the Earth and the Sun is measured in astronomical units. 1 UA = 149,597,871 km
- The distance travelled by light in one average solar year is measured in light-years. 1 light-year = 9,461,000,000,000 km
- A parsec is an astronomical unit of measurement. 1 parsec = 30,857,000,000,000 km
Important Questions Based on Unit of Length
Ques: What is the difference between Ao and A.U.? (1 Mark)
Ans: Ao and A.U. both are units of length. The major difference between both of the units is- 1Ao = 10-10m and 1 A.U. = 1.496 x 1011m.
Ques: Do A.U. and Ao represents the same magnitudes of length? (1 Mark)
Ans: No, A.U. and Ao do not represent the same magnitudes of length 1 A.U. = 1.496 x 1011 m and 1 Ao= 10-10 m.
Ques: Suggest a length corresponding to each of the following order of length:
(a) 10-4 m
(b) 10-9 m
(c) 104 m
(d) 107 m
(e) 109 m. (2 Marks)
Ans: (a) Size of the atomic nucleus
(b)Size of the oil molecule
(c) Height of Mount Everest
(d) Radius of Earth
(e) The radius of the Sun.
Ques: Define dimensions of a physical quantity. (2 Marks)
Ans: Dimensions of a physical quantity are defined as the powers to which the fundamental units of mass, length, and time have to be raised to obtain its units. For Example- The unit of area is [M0 L2 T0]. Thus its dimensions are 1 zero in mass, 2 in length, and zero in time.
Ques: Define standard meter. (2 Marks)
Ans: Standard meter is equal to exactly 1650763.73 wavelengths of orange-red light emitted in vacuum by krypton-86 atom i.e. kr86.
- e. 1 metre = 16,50,763.73 wavelengths.
It is also defined as the distance traveled by light in 1/299792458 seconds.
Here, the exact value of the velocity of light is 299792458 ms-1.
Practically, c = 2.9 × 108 ms-1 = 3.0 × 108 ms-1.
Ques: Define one parsec. (2 Marks)
Ans: One parsec is defined as the distance at which an arc of length equal to one astronomical unit subtends an angle of one second at a point.
Ques: The unit of length convenient on the atomic scale is known as an angstrom and is denoted by Ao (1Ao = 10-10 m). The size of a hydrogen atom is about 0.5 Ao what is the total atomic volume in m3 of a mole of hydrogen atoms? (3 Marks)
Ans: Radius of hydrogen atom, r = 0.5 Ao = 0.5 x 10-10 m =
Volume of hydrogen atom =4/3π r3
= 4/3 x 22/7 x (0.5x 10-10 )3
= 0.524 x 10-30m3
1 mole of hydrogen has 6.023 x 1023 hydrogen atoms.
∴ Volume of 1 mole of hydrogen atoms = 6.023 x 1023 x 0.524 x 10-30
= 3.16 x 10-7 m3
Ques: Convert the following- (3 Marks)
- 5 cm to mm
- 10 m to cm
- 15 km to m
Ans: a) 5 cm to mm –
We know, 1 cm=10 mm
5cm = 5 * 10 = 50 mm.
- 10m to cm-
We know, 1m = 100 cm
10m = 10 * 100 = 1000cm .
- 15km to m
We know, 1 km = 1000m
15km = 15 * 1000 = 15000m
Ques: Convert the following -
- 52.8 cm to mm
- 68.7 m to cm
- 6.26 m to mm
- 8.75 km to mm (4 Marks)
Ans: a) 52.8 cm to mm
1 cm = 10 mm
52.8 cm = 52.8 * 10 = 528mm
- 68.7 m to cm
1m = 100 cm
7 m = 68.7 * 100 = 6870 cm
- 6.26 m to mm
1 m = 10 mm
26 m = 6.26 * 10 = 62.6 mm.
- 8.75 km to mm
1 km = 1000 m
75 km = 8.75 * 1000 = 8750m
1m = 100 cm
8750 m = 8750 * 100= 875000 cm
1 cm = 10 mm
875000 cm = 875000 * 10 = 8750000 mm
Comments