Electrical Units

Reference data and engineering information about electrical units for electrical applications.

electricalunits

Overview

Engineering reference data for Electrical Units in electrical engineering.

Key Formulas

Power

$P = VI = I^2R = V^2/R$

Electrical power.

Variables

Symbol	Description	Unit
$V$	Voltage	V
$I$	Current	A
$R$	Resistance	Ω
$P$	Power	W

Unit Definitions and Properties

Beyond basic definitions, understanding the relationships and physical meanings of electrical units is crucial for practical applications.

Ampere (A)

The ampere is defined through the force between current-carrying conductors. A current of 1 A represents a flow of 1 coulomb of charge per second. This relationship is fundamental: $I = \frac{Q}{t}$

The coulomb is the SI unit of electric charge. One coulomb is equivalent to the charge of approximately $6.24 \times 10^{18}$ electrons. The relationship between charge, current, and time is: $Q = I \cdot t$

Farad (F)

The farad is a large unit; practical capacitors are measured in microfarads ( $\mu\text{F}$ ) or picofarads (pF). Capacitance defines the ability to store charge per unit voltage: $C = \frac{Q}{V}$ For a capacitor, current flow is proportional to the rate of voltage change: $I = C \frac{dV}{dt}$

Henry (H)

Like the farad, the henry is large for typical circuits, so millihenries (mH) and microhenries ( $\mu\text{H}$ ) are common. Inductance describes a component's ability to store energy in a magnetic field, opposing changes in current: $V = L \frac{dI}{dt}$

Volt (V)

The volt is the unit of electric potential difference. One volt is the potential needed to drive one ampere of current through one ohm of resistance. The base SI unit derivation is: $1 \, \text{V} = 1 \, \frac{\text{kg} \cdot \text{m}^2}{\text{s}^3 \cdot \text{A}}$

Common Unit Conversions

Quantity	Unit	Symbol	Conversion
Current	ampere	A	Base unit
	milliampere	mA	$1 \, \text{mA} = 10^{-3} \, \text{A}$
	microampere	$\mu\text{A}$	$1 \, \mu\text{A} = 10^{-6} \, \text{A}$
	nanoampere	nA	$1 \, \text{nA} = 10^{-9} \, \text{A}$
	picoampere	pA	$1 \, \text{pA} = 10^{-12} \, \text{A}$
Capacitance	farad	F	Base unit
	microfarad	$\mu\text{F}$	$1 \, \mu\text{F} = 10^{-6} \, \text{F}$
	picofarad	pF	$1 \, \text{pF} = 10^{-12} \, \text{F}$
Inductance	henry	H	Base unit
	millihenry	mH	$1 \, \text{mH} = 10^{-3} \, \text{H}$
	microhenry	$\mu\text{H}$	$1 \, \mu\text{H} = 10^{-6} \, \text{H}$
	nanohenry	nH	$1 \, \text{nH} = 10^{-9} \, \text{H}$
Voltage	volt	V	Base unit
	kilovolt	kV	$1 \, \text{kV} = 10^{3} \, \text{V}$
	millivolt	mV	$1 \, \text{mV} = 10^{-3} \, \text{V}$
	microvolt	$\mu\text{V}$	$1 \, \mu\text{V} = 10^{-6} \, \text{V}$

Measurement Techniques

Accurate measurement requires connecting instruments correctly within the circuit.

Ammeter: Measures current ( $I$ ) and must be connected in series with the circuit element. Placing it in parallel can short-circuit the component and damage the meter.
Voltmeter: Measures potential difference ( $V$ ) and must be connected in parallel across the component whose voltage is to be measured.

References

Original Source

Source: engineeringtoolbox.com