# Power in electrical DC circuits - examples

Collection of exercices which are about power P in electrical DC circuits. In DC circuits formula for power is quite simple because it is a multiply of voltage U and current I → P=U·I. Power in electrical DC circuits represents heat produced on resistance R or mechanical energy in electrical motors. Power is a measure how work W is changing in time → P=W/t. Unit of power P is Watt → [W]. Temporary power p is defined as p=dW/dt. From formula for temporary power p, a fromula work is possible to designate → W=∫p·dt. Unit of work W is Joule [J]=[W·s].

## Maximum power on load resistor

Derivation of formula for maximum power on load resistor. Simple electric circuit is considered in example. Electrical circuit is built from voltage source E, internal resistance of voltage source R_{l} and load resistor R_{l}. In example condition will be found which allow for releasing a maximum power on load resistor.

Maximum power on load resistor