All electrical quantities

Prof. Dr. Thorsten Jungmann (last updated 2025-11-16)

The EE1 script introduces 36 physical and electrical engineering quantities.
EE2 adds 11 more.

Each quantity usually comes with the following information:

• What is it called? – Name / designation (German and English)
• Which physical or technical phenomenon does it represent?
• How is it represented? – Quantity symbol and unit
• How is it used in electrical engineering? – Practical and calculation examples, common orders of magnitude and example phrasings
• Where does it play a special role? – Formulas and components

1 Relevant quantities in EE1 (fundamentals)

1.1 Base quantities

Separate overview page
SI prefixes

• Length $l$ in metres ($\mathrm{m}$)
• Mass $m$ in kilograms ($\mathrm{kg}$)
• Time $t$ in seconds ($\mathrm{s}$)
• Current $I$ in amperes ($\mathrm{A}$)
• Temperature $T$ in kelvins ($\mathrm{K}$)
• Amount of substance $n$ in moles ($\mathrm{mol}$)
• Luminous intensity $I_v$ in candelas ($\mathrm{cd}$)

1.2 Basic electrical quantities

• Electric charge $Q$ in coulombs ($\mathrm{C}$)
• Electric potential $\phi$ in volts ($\mathrm{V}$)
• Voltage $U$ in volts ($\mathrm{V}$)
• Force $F$ in newtons ($\mathrm{N}$)

1.3 Current and conductivity

• Current density $J$ in amperes per square metre ($\mathrm{A}/{\mathrm{m}}^2$)
• Resistance $R$ in ohms ($\Omega$)
• Resistivity $\rho$ in ohm metres ($\Omega \mathrm{m}$)
• Conductance $G$ in siemens ($\mathrm{S}$)
• Conductivity $\sigma$ in siemens per metre ($\mathrm{S}/\mathrm{m}$)

1.4 Power and energy

• Active power $P$ in watts ($\mathrm{W}$)
• Energy $W$ in watt-seconds ($\mathrm{Ws}$)
• Efficiency $\eta$, dimensionless (1)

1.5 Electrostatic fields

• Electric field strength $E$ in volts per metre ($\mathrm{V}/\mathrm{m}$)
• Electric flux $\Psi$ in ampere-seconds ($\mathrm{A}\mathrm{s}$)
• Electric flux density $D$ in ampere-seconds per square metre ($\mathrm{A}\mathrm{s}/{\mathrm{m}}^2$)
• Capacitance $C$ in farads ($\mathrm{F}$)
• Permittivity $\epsilon$ in farads per metre ($\mathrm{F}/\mathrm{m}$)

1.6 Magnetic fields

• Magnetic field strength $H$ in amperes per metre ($\mathrm{A}/\mathrm{m}$)
• Magnetic flux density $B$ in teslas ($\mathrm{T}$)
• Magnetic flux $\Phi$ in webers ($\mathrm{Wb}$)
• Magnetomotive force $\Theta$ in amperes ($\mathrm{A}$)
• Reluctance $R_m$ in amperes per weber ($A/Wb$)
• Inductance $L$ in henries ($\mathrm{H}$)
• Permeability $\mu$ in henries per metre ($\mathrm{H}/\mathrm{m}$)
• Number of turns $N$, dimensionless (1)

1.7 Other quantities

• Number of entities $n$, dimensionless (1)
• Area $A$ in square metres ($m^2$)
• Cost $K$ in EUR
• Velocity $v$ in metres per second $m/s$

2 Relevant quantities in EE2 (AC circuit analysis)

• Frequency $f$ in hertz ($\mathrm{Hz}$)
• Wavelength $\lambda$ in metres ($\mathrm{m}$)
• Rotational frequency $n$ in 1 per minute ($\mathrm{mi}{\mathrm{n}}^{-1}$)
• Angular frequency $\omega$ in reciprocal seconds (${\mathrm{s}}^{-1}$)
• Reactance $X$ in ohms ($\Omega$)
• Apparent impedance $Z$ in ohms ($\Omega$)
• Reactive power $Q$ in volt-amperes reactive ($\mathrm{var}$)
• Apparent power $S$ in volt-amperes ($\mathrm{VA}$)
• Power factor $\cos \phi$, dimensionless (1)
• Reactive factor $\sin \phi$, dimensionless (1)
• Phase angle $\phi$ in degrees or radians

3 Physical constants

In addition to the quantities listed above, the following physical constants are used in the formulas and equations:

• Elementary charge $e\approx 1.6022\cdot 10^{-19}\text{A}\text{s}$
• Circle constant $\pi \approx 3.1416$
• Permeability of the vacuum (vacuum permeability) ${\mu }_0\approx 1.2566\cdot 10^{-6}\text{H/m}$
• Permittivity of the vacuum (electric field constant) ${\epsilon }_0\approx 8.8542\cdot 10^{-12}\text{F/m}$
• Speed of light $c\approx 300000000\text{m/s}$

Naming of quantities

In this script, quantities are named in a pragmatic engineering manner – that is: as precisely as necessary and as briefly as possible.

The electric voltage is simply called ‘voltage’ in the script, because it cannot be confused with mechanical stress. The same goes for electric charge, which is simply called ‘charge’ – after all, we are not in freight logistics.

Where a quantity occurs in both a magnetic and an electric form, such as the field strength or the magnetomotive force, this is made clear in its name – we therefore distinguish between the electric field strength and the magnetic field strength.