Ohm's law

(noun)

Ohm's observation is that the direct current flowing in an electrical circuit consisting only of resistances is directly proportional to the voltage applied.

Examples of Ohm's law in the following topics:

  • Ohm's Law

    • This important relationship is known as Ohm's law.
    • This relationship is also called Ohm's law.
    • Ohm's law (like Hooke's law) is not universally valid.
    • The many substances for which Ohm's law holds are called ohmic.
    • The other two devices do not follow Ohm's law.

  • Current and Voltage Measurements in Circuits

    • According to Ohm's law, The electrical current I, or movement of charge, that flows through most substances is directly proportional to the voltage V applied to it.
    • Ohm's law can therefore be written as follows:
    • More specifically, Ohm's law states that R in this relation is constant, independent of the current.
    • To solve this problem, we would just substitute the given values into Ohm's law: I = 1.5V/5Ω; I = 0.3 amperes.
    • If we know the current and the resistance, we can rearrange the Ohm's law equation and solve for voltage V:

  • Resistors in AC Circuits

    • In a circuit with a resistor and an AC power source, Ohm's law still applies (V = IR).
    • Ohm's law applies to AC circuits as well as to DC circuits.
    • Apply Ohm's law to determine current and voltage in an AC circuit

  • Capacitors in AC Circuits: Capacitive Reactance and Phasor Diagrams

    • There, we used the Ohm's law (V=IR) to derive the relationship between voltage and current in AC circuits.
    • In this and following Atoms, we will generalize the Ohm's law so that we can use it even when we have capacitors and inductors in the circuit.
    • Because it is still a voltage divided by a current (like resistance), its unit is the ohm.
    • This is considered to be an effective resistance of the capacitor to AC, and so the rms current Irms in the circuit containing only a capacitor C is given by another version of Ohm's law to be $I_{rms} = \frac{V_{rms}}{X_C}$, where Vrms is the rms voltage.
    • Note that XC replaces R in the DC version of the Ohm's law.

  • Resisitors in Series

    • Using Ohm's Law to Calculate Voltage Changes in Resistors in Series
    • According to Ohm's law, the voltage drop, V, across a resistor when a current flows through it is calculated by using the equation V=IR, where I is current in amps (A) and R is the resistance in ohms (Ω).
    • A brief introduction to series circuit and series circuit analysis, including Kirchhoff's Current Law (KCL) and Kirchhoff's Voltage Law (KVL).

  • Resistors in Parallel

    • According to Ohm's law, the currents flowing through the individual resistors are $I_1 = \frac{V}{R_1}$, $I_2 = \frac{V}{R_2}$, and $I_3 = \frac{V}{R_3}$.

  • RLC Series Circuit: At Large and Small Frequencies; Phasor Diagram

    • By combining Ohm's law (Irms=Vrms/Z; Irms and Vrms are rms current and voltage) and the expression for impedance Z, from:
    • This response makes sense because, at high frequencies, Lenz's law suggests that the impedance due to the inductor will be large.

  • Different Types of Currents

    • A number of electrical laws apply to all electrical networks.
    • These include Ohm's law, which has been discussed in the "Resistance and Resistors" module, Kirchhoff's current and voltage laws, which are covered in the "Kirchhoff's Rules" module.
    • The two Kirchoff laws along with the current-voltage characteristic (I-V curve) of each electrical element completely describe a circuit.
    • The current i flowing through the circuit is given by Ohm's law.

  • Inductors in AC Circuits: Inductive Reactive and Phasor Diagrams

    • In an AC circuit with an inductor, the voltage across an inductor "leads" the current because of the Lenz' law.
    • The rms current Irms through an inductor L is given by a version of Ohm's law: $I_{rms} = \frac{V_{rms}}{X_L}$ where Vrms is the rms voltage across the inductor and $X_L = 2\pi \nu L$ with $\nu$ the frequency of the AC voltage source in hertz.
    • Because the inductor reacts to impede the current, XL has units of ohms (1 H=1 Ωs, so that frequency times inductance has units of (cycles/s)(Ωs)=Ω), consistent with its role as an effective resistance.
    • The voltage across an inductor "leads" the current because of the Lenz's law.

  • Introduction and Importance

    • Kirchhoff's circuit laws are two equations first published by Gustav Kirchhoff in 1845.
    • Kirchhoff, rather, used Georg Ohm's work as a foundation for Kirchhoff's current law (KCL) and Kirchhoff's voltage law (KVL).
    • Kirchhoff's laws are extremely important to the analysis of closed circuits.
    • As a final note, Kirchhoff's laws depend on certain conditions.
    • The voltage law is a simplification of Faraday's law of induction, and is based on the assumption that there is no fluctuating magnetic field within the closed loop.