Quantities, Units and Symbols

 

QUANTITY	SYMBOL	SI UNIT	SYMBOL	DERIVATION
acceleration	a	m s ^-2	–	velocity/time
acceleration due to gravity	g	m s^-2	–	velocity/time
amount of substance	n	mole	mol	mole fraction (n) used
amplification factor	μ	a ratio	–	–
angle	θ p φpα1	–	–	–
– of incidence	i	degree or radian	°	–
– of refraction	r	degree or radian	°	–
– Bragg	θ	number	–	–
– critical	с	degree or radian	°	–
anode slope resistance	RA	ohm	Ω	ДV a /ДV a
area	A	metres square	m^2	l x b
atomic number	Z	a number	–	number of protons
Avogadro constant	L, NA	number	–	–
breadth	b	metre	m	fundamental unit
capacitance	С	farad	F	charge/p.d.
charge, electric	Q	coulomb	С	current x time
on electron	e	coulomb	С	l.6 x 10^-19C
conductance	G	ohm^-1	Ω^-1	reciprocal of resistance
current, electric	I	ampere	A	fundamental unit
decay constant	λ	a ratio	–	–
density	ρ	kg m^-3	–	m/V
distance along path	s	metre	m	fundamental unit
efficiency	η	a ratio	–	work output/ work input
electrochemical equivalent	z	gC^-1	–	mass/charge
electromotive force	E	volt	V	energy/charge
electron	e
energy	E	joule	J	N m
– kinetic	Ek	joule	J	N m.Ek=Smv^2
– potential	Ep	joule	J	N m.Ep=mgh
Faraday constant	F	coulomb mol^-1	C mol^-1	96 500 С mol^-1
field strength,	E	Vm^-1	–	potential gradient:
electric				p.d./dist.
magnetic	H	ampereturns	–	current no. of turns
flux, magnetic	Ф	weber	Wb	e.m.f./rate of change of flux
flux density	В	tesla	Т	flux/area
focal length	f	metre	M	–
force	F	newton	N	kg m s^-2
free energy	ΔG	joule	J
frequency	f	hertz	Hz	oscillations/ time
gas constant	r	joule	J	energy
half-life, radioactivity	t1/2	second	s	fundamental unit
heat capacity	С	JK^-1	–	quantity of heat/ temp. rise
heat of reaction	ΔH	joule	J	heat energy
heat capacity, specific	с	J K^-1kg^-1	–	heat capacity/ mass
heat, quantity of	q	joule	J	energy
height	h	metre	m	fundamental unit
image distance	v	metre	m	fundamental unit
inductance, mutual	M	henry	H	induced e.m.f./rate of change of current
self	L	henry	H	–
intensity of radiation	I	a number	–	–
latent heat	L	joule	J	quantity of heat
–, specific	l	J kg^-1	–	quantity of heat
–, molar	Lm	joule mol^-1	J	quantity of heat
length	l	metre	m	fundamental unit
magnetizing force	H	ampereturns	–	–
magnetic moment	m	Wb m	–	torque in unit magnetic field
magnification, linear	m	a ratio	–	–
mass	m	kilogramme	kg	fundamental unit
– number	A	a number	–	number of neutrons + protons
molar volume	Vm	(dm^3)	–	volume of 1 mole
molar solution	M	a ratio		moles/dm^3
moment of force	–	N m	–	force perp. distance
neutron number	N	a number	–	number of neutrons
number	n	–	–	–
– of molecules	N	–	–	–
– of turns on coil	n	a number	–	–
– order of spectrum	p	a number	–	–
object distance	u	metre	m	fundamental unit
peak current	I0	ampere	A	see current
peak e.m.f.	E0	volt	V	see e.m.f.
period	Т	second	s	fundamental unit
permeability	μ	H m^-1	–	henry/metre
– of vacuum	μ0	H m^-1	–	–
–, relative	μr	a ratio	–	м = м / м0
permittivity	ε	F m^-1	–	farad/metre
– of vacuum	ε 0	F m^-1	–	farad/metre
–, relative	ε r	a ratio	–	е r = е / е 0
potential, electric	V	volt	V	energy/charge
potential difference	V	volt	V	energy/charge
power	P	watt	W	J s^-1
pressure	p	pascal	Pa	Nm^-2: force/area
radius	r	metre	m	fundamental unit
reactance	X	ohm	Ω	E0 /l0
refractive index	n	a ratio	–	–
resistance	R	ohm	Ω	p.d./current
resistivity, electrical	ρ	ohm-metre		resistance x length
relative density	d	a ratio	–	сsub / сwater
r.m.s. current	Irms	ampere	A	see current
r.m.s. voltage	Vrms	volt	V	see e.m.f.
slit separation	S	metre	m	fundamental unit
tension	Т	newton	N	see force
temperature, Celsius	θ	degree С	°C	from kelvin
temp., interval	θ	degree	° or K	–
temp., absolute	T	kelvin	К	fundamental unit
thickness	d	metre	m	fundamental unit
time	t	second	s	fundamental unit
torque	T	N m	–	see moment
turns ratio	Т	a ratio	–	nsec / nprim
(unit of electricity)	–	kWh	–	kilowatt hour
velocity	u, v	m s^-1	–	distance/time
–, angular	ω	second ^-1	s^-1	angle/time
– of e.m. waves	c	m s^-1	–	–
– of sound		m s^-1	–	–
volume	V	metre cubed	m^3	l b h
wavelength	λ	metre	m	fundamental unit
work	w	joule	J	force x distance (N • m)
weight	W	newton	N	kg m s^-2 or mg

 

Appendix 10