# Fundamental Physics/Electricity/Electric circuits/Electric circuit theorem

## Norton's theorem Any network of voltage or current sources and resistors is electrically equivalent to an ideal current source in parallel with a single resistor.


## Thévenin's theorem Any network of voltage or current sources and resistors is electrically equivalent to a single voltage source in series with a single resistor.


## Superposition theorem

In a linear network with several independent sources, the response in a particular branch when all the sources are acting simultaneously is equal to the linear sum of individual responses calculated by taking one independent source at a time.


Other more complex laws may be needed if the network contains nonlinear or reactive components. Non-linear self-regenerative heterodyning systems can be approximated. Applying these laws results in a set of simultaneous equations that can be solved either algebraically or numerically.

## Maximum power transfer theorem

Maximum power transfer is achieved when resistance of the load is equal to resistance of the source  The condition of maximum power transfer does not result in maximum efficiency.

If we define the efficiency η as the ratio of power dissipated by the load to power developed by the source, then it is straightforward to calculate from the above circuit diagram that

$\eta ={\frac {R_{\mathrm {load} }}{R_{\mathrm {load} }+R_{\mathrm {source} }}}={\frac {1}{1+R_{\mathrm {source} }/R_{\mathrm {load} }}}.$ 