Electrical Voltage
Electrical voltage is defined as electric potential difference between two points of an electric field.
Using water pipe analogy, we can visualize the voltage as height difference that makes the water flow down.
V = φ2 - φ1
V is the voltage between point 2 and 1 in volts (V).
φ2 is the electric potential at point #2 in volts (V).
φ1 is the electric potential at point #1 in volts (V).
In an electrical circuit, the electrical voltage V in volts (V) is equal to the energy consumption E in joules (J)
divided by the electric charge Q in coulombs (C).
V is the voltage measured in volts (V)
E is the energy measured in joules (J)
Q is the electric charge measured in coulombs (C)
Voltage in series
The total voltage of several voltage sources or voltage drops in series is their sum.
VT = V1 + V2 + V3 +...
VT - the equivalent voltage source or voltage drop in volts (V).
V1 - voltage source or voltage drop in volts (V).
V2 - voltage source or voltage drop in volts (V).
V3 - voltage source or voltage drop in volts (V).
Voltage in parallel
Voltage sources or voltage drops in parallel have equal voltage.
VT = V1 = V2 = V3 =...
VT - the equivalent voltage source or voltage drop in volts (V).
V1 - voltage source or voltage drop in volts (V).
V2 - voltage source or voltage drop in volts (V).
V3 - voltage source or voltage drop in volts (V).
Voltage divider
For electrical circuit with resistors (or other impedance) in series, the voltage drop Vi on resistor Ri is:
Kirchhoff's voltage law (KVL)
The sum of voltage drops at a current loop is zero.
∑ Vk = 0
DC circuit
Direct current (DC) is generated by a constant voltage source like a battery or DC voltage source.
The voltage drop on a resistor can be calculated from the resistor's resistance and the resistor's current, using Ohm's law:
Voltage calculation with Ohm's law
VR = IR × R
VR - voltage drop on the resistor measured in volts (V)
IR - current flow through the resistor measured in amperes (A)
R - resistance of the resistor measured in ohms (Ω)
AC circuit
Alternating current is generated by a sinusoidal voltage source.
Ohm's law
VZ = IZ × Z
VZ - voltage drop on the load measured in volts (V)
IZ - current flow through the load measured in amperes (A)
Z - impedance of the load measured in ohms (Ω)
Momentary voltage
v(t) = Vmax × sin(ωt+θ)
v(t) - voltage at time t, measured in volts (V).
Vmax - maximal voltage (=amplitude of sine), measured in volts (V).
ω - angular frequency measured in radians per second (rad/s).
t - time, measured in seconds (s).
θ - phase of sine wave in radians (rad).
RMS (effective) voltage
Vrms = Veff = Vmax / √2 ≈ 0.707 Vmax
Vrms - RMS voltage, measured in volts (V).
Vmax - maximal voltage (=amplitude of sine), measured in volts (V).
Peak-to-peak voltage
Vp-p = 2Vmax
Voltage drop
Voltage drop is the drop of electrical potential or potential difference on the load in an electrical circuit.
Voltage Measurement
Electrical voltage is measured with Voltmeter. The Voltmeter is connected in parallel to the measured component or circuit.
The voltmeter has very high resistance, so it almost does not affect the measured circuit.
Voltage by Country
AC voltage supply may vary for each country.
European countries use 230V while north America countries use 120V.
Country Voltage [Volts]
Frequency [Hertz]
Australia 230V 50Hz Brazil 110V 60Hz Canada 120V 60Hz China 220V 50Hz France 230V 50Hz Germany 230V 50Hz India 230V 50Hz Ireland 230V 50Hz Israel 230V 50Hz Italy 230V 50Hz Japan 100V 50/60Hz New Zealand 230V 50Hz Philippines 220V 60Hz Russia 220V 50Hz South Africa 220V 50Hz Thailand 220V 50Hz UK 230V 50Hz USA 120V 60Hz Electrical current ►
See also
Online Reference & Tools
