Voltage

(noun)

The measure of potential energy generated by separated charge.

Related Terms

Examples of Voltage in the following topics:

  • EMF and Terminal Voltage

    • The output, or terminal voltage of a voltage source such as a battery, depends on its electromotive force and its internal resistance.
    • presents a schematic representation of a voltage source.
    • The voltage output of a device is measured across its terminals and is called its terminal voltage V.
    • Terminal voltage is given by the equation:
    • The larger the current, the smaller the terminal voltage.

  • Inductors in AC Circuits: Inductive Reactive and Phasor Diagrams

    • The graph shows voltage and current as functions of time.
    • (b) starts with voltage at a maximum.
    • Note that the current starts at zero, then rises to its peak after the voltage driving it (as seen in the preceding section when DC voltage was switched on).
    • When the voltage becomes negative at point a, the current begins to decrease; it becomes zero at point b, where voltage is its most negative.
    • Hence, when a sinusoidal voltage is applied to an inductor, the voltage leads the current by one-fourth of a cycle, or by a 90ยบ phase angle.

  • Resistors and Capacitors in Series

    • Fig 1 shows a simple RC circuit that employs a DC voltage source.
    • In terms of voltage, across the capacitor voltage is given by Vc=Q/C, where Q is the amount of charge stored on each plate and C is the capacitance.
    • When there is no current, there is no IR drop, so the voltage on the capacitor must then equal the emf of the voltage source.
    • where V(t) is the voltage across the capacitor and emf is equal to the emf of the DC voltage source.
    • Initially, the current is I0=V0/R, driven by the initial voltage V0 on the capacitor.

  • Ohm's Law

    • The phrase IR drop is often used for this voltage.
    • If voltage is measured at various points in a circuit, it will be seen to increase at the voltage source and decrease at the resistor.
    • Voltage is similar to fluid pressure.
    • If voltage is forced to some value V, then that voltage V divided by measured current I will equal R.
    • The voltage drop across a resistor in a simple circuit equals the voltage output of the battery.

  • Current and Voltage Measurements in Circuits

    • The electrical current is directly proportional to the voltage applied and inversely related to the resistance in a circuit.
    • A simple circuit consists of a voltage source and a resistor and can be schematically represented as in .
    • Using this equation, we can calculate the current, voltage, or resistance in a given circuit.
    • A simple electric circuit made up of a voltage source and a resistor
    • Describe the relationship between the electrical current, voltage, and resistance in a circuit

  • Transformers

    • Because high voltages pose greater hazards, transformers are employed to produce lower voltage at the user's location.
    • In normal use, the input voltage is placed on the primary, and the secondary produces the transformed output voltage.
    • Since the input voltage is AC, a time-varying magnetic flux is sent to the secondary, inducing its AC output voltage.
    • A step-up transformer is one that increases voltage, whereas a step-down transformer decreases voltage.
    • So if voltage increases, current decreases.

  • Phase Angle and Power Factor

    • In a series RC circuit connected to an AC voltage source, voltage and current maintain a phase difference.
    • On the other hand, because the total voltage should be equal to the sum of voltages on the resistor and capacitor, so we have:
    • where $\omega$ is the angular frequency of the AC voltage source and j is the imaginary unit; j2=-1.
    • we notice that voltage $v(t)$ and current $i(t)$ has a phase difference of $\phi$.
    • Because voltage and current are out of phase, power dissipated by the circuit is not equal to: (peak voltage) times (peak current).

  • Resistors in AC Circuits

    • It is the steady state of a constant-voltage circuit.
    • Therefore, with an AC voltage given by:
    • In this example, in which we have a resistor and the voltage source in the circuit, the voltage and current are said to be in phase, as seen in (b).
    • The frequencies and peak voltages of AC sources differ greatly.
    • Apply Ohm's law to determine current and voltage in an AC circuit

  • Root Mean Square Values

    • The root mean square (RMS) voltage or current is the time-averaged voltage or current in an AC system.
    • Unlike direct current (DC), where the currents and voltages are constant, AC currents and voltages vary over time.
    • V is the voltage at time t, V0 is the peak voltage, and f is the frequency in hertz.
    • The frequencies and peak voltages of AC sources differ greatly.
    • Relate the root mean square voltage and current in an alternating circut with the peak voltage and current and the average power

  • Impedance

    • The phase of the complex impedance is the phase shift by which the current is ahead of the voltage.
    • From our voltage given above, $i = \frac{V}{R} e^{j \omega t}$.
    • Thus the resistor's voltage is a complex, as is the current with an amplitude $I = \frac{V}{R}$.
    • Letting the voltage be a complex exponential we have $i = j \omega CV e^{j \omega t}$.
    • The magnitude of the complex impedance is the ratio of the voltage amplitude to the current amplitude.