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The total resistance of this parallel arrangement is expressed by the following equation: 1/R total = 1/R a + 1/R b + ... + 1/R n. R a, R b, and R n are the resistances of the renal, hepatic, and other arteries respectively. The total resistance is less than the resistance of any of the individual arteries. [3]
If the resistance is not constant, the previous equation cannot be called Ohm's law, but it can still be used as a definition of static/DC resistance. [4] Ohm's law is an empirical relation which accurately describes the conductivity of the vast majority of electrically conductive materials over many orders of magnitude of current.
A general formula for the current I X in a resistor R X that is in parallel with a combination of other resistors of total resistance R T (see Figure 1) is [1] = +, where I T is the total current entering the combined network of R X in parallel with R T.
This is equivalent to calculating the Thevenin resistance. When there are dependent sources, the more general method must be used. The voltage at the terminals is calculated for an injection of a 1 ampere test current at the terminals. This voltage divided by the 1 A current is the Norton impedance R no (in ohms). This method must be used if ...
Even if the material's resistivity is known, calculating the resistance of something made from it may, in some cases, be much more complicated than the formula = / above. One example is spreading resistance profiling , where the material is inhomogeneous (different resistivity in different places), and the exact paths of current flow are not ...
This is a particularly important transform for finding equivalent impedances. Its importance arises from the fact that the total impedance between two terminals cannot be determined solely by calculating series and parallel combinations except for a certain restricted class of network. In the general case additional transformations are required.
In electrical engineering, Millman's theorem [1] (or the parallel generator theorem) is a method to simplify the solution of a circuit. Specifically, Millman's theorem is used to compute the voltage at the ends of a circuit made up of only branches in parallel .
The resistance is measured after replacing all voltage- and current-sources with their internal resistances. That means an ideal voltage source is replaced with a short circuit, and an ideal current source is replaced with an open circuit. Resistance can then be calculated across the terminals using the formulae for series and parallel circuits ...