Electrical Power, in a circuit is the amount of energy that is absorbed or produced within the circuit. A source of energy such as a voltage will produce or deliver power while the connected load absorbs it. Light bulbs and heaters for example, absorb electrical power and convert it into heat or light. The higher their value or rating in watts the more power they will consume.
\subsection{Ohm's law}
Ohm's Law deals with the relationship between voltage and current in an ideal conductor. This relationship states that: The potential difference (voltage) across an ideal conductor is proportional to the current through it. The constant of proportionality is called the \textit{resistance}.
$$I =\frac U R $$
where I is the current expressed in Amperes [A], V is the voltage, bearing the Volt units [V] and R is the electrical resistance in ohms [$\Omega$].
The Ohms's law can be further expanded, to get these three quantities in relationship with power, such as
$$P = IV = I^2R =\frac{V^2}R$$
\subsection{Direct current (DC) circuits}
Generally, Ohm's law is used on direct current (DC) circuits. A DC voltage or current has a fixed magnitude (amplitude) and a definite direction associated with it. Both DC currents and voltages are produced by power supplies, batteries, dynamos and solar cells to name a few.
We also know that DC power supplies do not change their value with regards to time, they are a constant value flowing in a continuous steady state direction. In other words, DC maintains the same value for all times and a constant uni-directional DC supply never changes or becomes negative unless its connections are physically reversed.
\subsection{Alternating current (AC) circuits}
When a reactance (either inductive or capacitive) is present in an AC circuit, the previous formula does not apply. The product of \gls{voltage} and \gls{current} is, instead, expressed in volt-amperes (VA). This product is known as the \textit{apparent power}.
Peter Babič
9 years ago