terminal voltage

Examples of terminal 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.
  • 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.
  • (Note that the script E stands for emf. ) Also shown are the output terminals across which the terminal voltage V is measured.

• The Battery

  • The electrical driving force across the terminals of a cell is known as the terminal voltage (difference) and is measured in volts.
  • The voltage of a battery is synonymous with its electromotive force, or emf.
  • Voltage is not the same as energy.
  • Voltage is the energy per unit charge.
  • Thus a motorcycle battery and a car battery can both have the same voltage (more precisely, the same potential difference between battery terminals), yet one stores much more energy than the other.

• Null Measurements

  • When measuring the EMF of a battery and connecting the battery directly to a standard voltmeter, as shown in , the actual quantity measured is the terminal voltage V.
  • A potentiometer is a null measurement device for measuring potentials (voltages).
  • A voltage source is connected to resistor R, passing a constant current through it.
  • Note that emfx opposes the other voltage source.
  • An analog voltmeter attached to a battery draws a small but nonzero current and measures a terminal voltage that differs from the EMF of the battery.

• Antennae

  • In transmission, a radio transmitter supplies an oscillating radio frequency electric current to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic waves (radio waves).
  • In reception, an antenna intercepts some of the power of an electromagnetic wave in order to produce a tiny voltage at its terminals.
  • This voltage is applied to a receiver to be amplified.

• Voltmeters and Ammeters

  • Voltmeters and ammeters are used to measure voltage and current, respectively.
  • Voltmeters and ammeters measure the voltage and current, respectively, of a circuit.
  • The value of R is determined by the maximum voltage that will be measured.
  • Since R and r are in parallel, the voltage across them is the same.
  • Note that terminal voltage is measured between points a and b.

• Sources of EMF

  • Electromotive force (EMF) is the voltage voltage generated by a battery or by the magnetic force according to Faraday's Law of Induction.
  • Formally, EMF is classified as the external work expended per unit of charge to produce an electric potential difference across two open-circuited terminals.
  • When current flows, however, the voltage across the terminals of the source of EMF is no longer the open-circuit value, due to voltage drops inside the device due to its internal resistance.
  • Again the EMF is countered by the electrical voltage due to charge separation.
  • If a load is attached, this voltage can drive a current.

• Humans and Electric Hazards

  • A short circuit is a low-resistance path between terminals of a voltage source.
  • Such an undesired contact with a high voltage is called a short.
  • Since current is proportional to voltage when resistance is fixed (Ohm's law), high voltage is an indirect risk for producing higher currents.
  • Very high voltage (over about 600 volts): This poses an additional risk beyond the simple ability of high voltage to cause high current at a fixed resistance.
  • A short circuit is an undesired low-resistance path across a voltage source.

• Ohm's Law

  • The phrase IR drop is often used for this voltage.
  • 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.
  • A simple electric circuit in which a closed path for current to flow is supplied by conductors (usually metal wires) connecting a load to the terminals of a battery, represented by the red parallel lines.
  • The voltage drop across a resistor in a simple circuit equals the voltage output of the battery.

• 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 90º 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.