Uttar Pradesh PSC Exam: SI Derived Units

Get unlimited access to the best preparation resource for IAS : Get detailed illustrated notes covering entire syllabus: point-by-point for high retention.

Examples of SI derived units whose names and symbols include SI derived units with special names and symbols

Derived quantityNameSymbol
dynamic viscositypascal secondPa x s
moment of forcenewton meterN x m
surface tensionnewton per meterN/m
angular velocityradian per secondrad/s
angular accelerationradian per second squaredrad/s2
heat flux density, irradiancewatt per square meterW/m2
heat capacity, entropyjoule per kelvinJ/K
specific heat capacity, specific entropyjoule per kilogram kelvinJ/ (kg x K)
specific energyjoule per kilogramJ/kg
thermal conductivitywatt per meter kelvinW/ (m x K)
energy densityjoule per cubic meterJ/m3
electric field strengthvolt per meterV/m
electric charge densitycoulomb per cubic meterC/m3
electric flux densitycoulomb per square meterC/m2
permittivityfarad per meterF/m
permeabilityhenry per meterH/m
molar energyjoule per moleJ/mol
molar entropy, molar heat capacityjoule per mole kelvinJ/ (mol x K)
exposure (x and rays)coulomb per kilogramC/kg
absorbed dose rategray per secondGy/s
radiant intensitywatt per steradianW/sr
radiancewatt per square meter steradianW/ (m2 x sr)
catalytic (activity) concentrationkatal per cubic meterkat/m3

Examples of SI derived units whose names and symbols include SI derived units with special names and symbols

Units outside the SI that are accepted for use with the SI

NameSymbolValue in SI units
minute (time)min1 min = 60 s
hourh1 h = 60 min = 3600 s
dayd1 d = 24 h = 86 400 s
degree (angle)°1° = (i/180) rad
minute (angle)1 = () ° = (i/10 800)rad
second (angle)1inch = () = (i/648 000) radinch
literL1 L = 1 dm3 = 10 − 3 m3
metric ton (a)t1 t = 103 kg
neperNp1 Np = 1
bel (b)B1 B = () ln 10 Np (c)
electronvolt (d)eV1 eV = 1.602 18 × 10 − 19 J, approximately
unified atomic mass unit (e)u1 u = 1.660 54 × 10 − 27 kg, approximately
astronomical unit (f)ua1 ua = 1.495 98 × 1011 m, approximately
  1. In many countries, this unit is called tonne.
  2. The bel is most commonly used with the SI prefix deci: 1 dB = 0.1 B.
  3. Although the neper is coherent with SI units and is accepted by the CIPM, it has not been adopted by the General Conference on Weights and Measures (CGPM, Conference Generale des Poids et Mesures) and is thus not an SI unit.
  4. The electronvolt is the kinetic energy acquired by an electron passing through a potential difference of 1 V in vacuum. The value must be obtained by experiment, and is therefore not known exactly.
  5. The unified atomic mass unit is equal to of the mass of an unbound atom of the nuclide 12C, at rest and in its ground state. The value must be obtained by experiment, and is therefore not known exactly.
  6. The astronomical unit is a unit of length. Its value is such that, when used to describe the motion of bodies in the solar system, the heliocentric gravitation constant is (0.017 202 098 95) 2 ua3 × d − 2. The value must be obtained by experiment, and is therefore not known exactly.

The liter in Table given in the previous page deserves comment. This unit and its symbol l were adopted by the CIPM in 1879. The alternative symbol for the liter, L, was adopted by the CGPM in 1979 in order to avoid the risk of confusion between the letter l and the number 1. Thus, although both l and L are internationally accepted symbols for the liter, to avoid this risk the preferred symbol for use in the United States is L. Neither a lowercase script letter l nor an uppercase script letter L are approved symbols for the liter.

Other units outside the SI that are currently accepted for use with the SI by NIST are given in Table 7. These units, which are subject to future review, should be defined in relation to the SI in every document in which they are used; their continued use is not encouraged. The CIPM currently accepts the use of all of the units given in Table 7 with the SI except for the curie, roentgen, rad, and rem. Because of the continued wide use of these units in the United States, NIST still accepts their use with the SI.

Other units outside the SI that are currently accepted for use with the SI, subject to further review

NameSymbolValue in SI units
1 nautical mile = 1852 mknot1 nautical mile per hour = () m/s
area1 a = 1 dam2 = 102 m2
hectareha1 ha = 1 hm2 = 104 m2
barbar1 bar = 0.1 MPa = 100 kPa = 1000 hPa = 105 Pa
Angstrom1 Å = 0.1 nm = 10 − 10 m
barnb1 b = 100 fm2 = 10 − 28 m2
curieCi1 Ci = 3.7 × 1010 Bq
roentgenR1 R = 2.58 × 10 − 4 C/kg
radrad1 rad = 1 cGy = 10 − 2 Gy
remrem1 rem = 1 cSv = 10 − 2 Sv

Developed by: