where J is the current density at a given location in a resistive material, E is the electric field at that location, and σ (sigma) is a material-dependent parameter called conductivity. This reformulation of Ohm`s law goes back to Gustav Kirchhoff. [5] When reactive elements such as capacitors, inductors or transmission lines are involved in a circuit to which alternating current or time-varying voltage or current is applied, the relationship between voltage and current becomes the solution of a differential equation, so that Ohm`s law (as defined above) does not apply directly, since this form contains only resistances of value R. no complex impedances that can contain a capacitance (C) or an inductor (L). The broader aspect of this concept that you need to understand here is that vector quantities are concepts we use to support our calculations. So sometimes we have to make exceptions to facilitate or, in some cases, even correct our calculations. After replacing R from the above equation in the previous equation, the continuous form of Ohm`s law for a uniform field (and uniform current density) oriented along the conductor is reduced to the more familiar form: this form of Ohm`s law, where Z takes the place of R, generalizes the simpler form. If Z is complex, only the actual part is responsible for heat dissipation. Replacing the 2 results above (for E and J respectively) in the continuous form shown at the beginning of this section: Ohm`s law was probably the most important of the earliest quantitative descriptions of the physics of electricity. We take that for granted today. When Ohm first published his work, this was not the case; Critics reacted to his handling of the issue with hostility. They called his work a “network of naked fantasies”[11] and the German Minister of Education proclaimed that “a teacher who preached such heresies was unworthy to teach science.” [12] The prevailing scientific philosophy in Germany at the time asserted that experiments need not be performed to develop an understanding of nature because nature is so well ordered, and that scientific truths can be derived by reason alone.

[13] Ohm`s brother, Martin, a mathematician, also fought against the German education system. These factors hindered acceptance of Ohm`s work, and his work was not widely accepted until the 1840s. However, Ohm was recognized for his contributions to science long before his death. For the common case of a continuous sinusoid, the parameter s is assumed to be j ω {displaystyle jomega }, which corresponds to a complex sinusoid A e j ω t {displaystyle Ae^{{mbox{ }}jomega t}}. The actual parts of these complex current and voltage waveforms describe the actual sinusoidal currents and voltages in a circuit, which can be in different phases due to the different complex scalars. Ohm`s law in the above form is an extremely useful equation in the field of electrical engineering/electronics because it describes how voltage, current, and resistance are connected at a “macroscopic” level, i.e. usually as circuit elements in an electrical circuit. Physicists who study the electrical properties of matter at the microscopic level use a closely related and more general vector equation, sometimes called Ohm`s law, with variables closely related to the scalar variables V, I, and R of Ohm`s law, but each of them being a function of position in the conductor. Physicists often use this continuous form of Ohm`s law:[35] Ohm`s law is often used in the study of electronics and electricity.

Therefore, it is important for students to remember the formulas as they help in circuit analysis. The above formulas of Ohm`s law can easily be recalled with the triangle of Ohm`s law. This triangle helps us to easily represent the interchangeability of equations. We can take a triangle and divide it into three parts. Then we can enter the values V, I, R in the triangle. V above, I left and R right. It will look like this; The vector form of Ohm`s law is used in electromagnetism and materials science. The vector form is given as follows: each equation is cited by some sources as a determining relation of Ohm`s law,[2][23][24] or all three are cited,[25] or derived from a proportional form,[26] or even only the two that do not correspond to Ohm`s original statement can sometimes be given. [27] [28] where “E” is the electric field vector with units of volts per meter (analogous to “V” of Ohm`s law, which has units of volts), “J” is the current density vector with units of amperes per unit area (analogous to “I” of Ohm`s law, which has units of amperes) and “ρ” (Greek “rho”) is the resistivity with units of ohm·meter (analogous to “R” of the Ohm`s law, which has units of ohms). The above equation is sometimes [36] written as J = σ {displaystyle sigma } E, where “σ” (Greek “sigma”) is conductivity, which is the inverse of ρ.

The law was named after the German physicist Georg Ohm, who described voltage and current measurements applied by simple electrical circuits with different wire lengths in a paper published in 1827. Ohm explained his experimental results by an equation slightly more complex than the modern form above (see § History below). with d l {displaystyle dmathbf {l} } is the element of the path along the integration of the electric field vector E. If the applied field E is oriented uniformly and along the length of the conductor, as shown in the figure, then we define the voltage V in the usual convention of being opposed to the field (see figure), and understanding that the voltage V is measured differentially over the length of the conductor, so that we can drop the symbol Δ, The above vector equation boils down to the scalar equation: since the field E is uniform in the direction of the wire length, for a conductor with a uniformly constant resistance ρ, the current density J is also aligned uniformly and in the direction of the wire length in each region of the cross-section, so that we can write:[38] Ohm`s law applies to circuits that contain only ohmic elements (no capacitances or inductors) for all forms of voltage or drive current. whether the drive voltage or drive current is constant (DC) or time-variable such as alternating current. At all times, Ohm`s Law applies to such circuits. In physics, the term Ohm`s law is also used to refer to various generalizations of the law; For example, the vector form of the law used in electromagnetism and materials science: in this approach, a voltage or current waveform takes the form Aest, where t is time, s is a complex parameter, and A is a complex scalar.