stopping voltage

Examples of stopping voltage in the following topics:

• 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.
  • Mutual repulsion of like charges in the capacitor progressively slows the flow as the capacitor is charged, stopping the current when the capacitor is fully charged and Q=C⋅emf.

• Capacitors in AC Circuits: Capacitive Reactance and Phasor Diagrams

  • The voltage across a capacitor lags the current.
  • We say that the current and voltage are in phase.
  • When a capacitor is connected to an alternating voltage, the maximum voltage is proportional to the maximum current, but the maximum voltage does not occur at the same time as the maximum current.
  • The capacitor is affecting the current, having the ability to stop it altogether when fully charged.
  • Since the voltage across a capacitor lags the current, the phasor representing the current and voltage would be give as in .

• 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 90º phase angle.

• RL Circuits

  • An RL circuit consists of an inductor and a resistor, in series or parallel with each other, with current driven by a voltage source.
  • A resistor-inductor circuit (RL circuit) consists of a resistor and an inductor (either in series or in parallel) driven by a voltage source.
  • (Note the similarity to the exponential behavior of the voltage on a charging capacitor.)
  • In position 2, the battery is removed and the current eventually stops because of energy loss in the resistor.
  • Describe current-voltage relationship in the RL circuit and calculate energy that can be stored in an inductor

• 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