Principles of Electricity

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Basic formulas calculating resistance, current, voltage, and power-
where:

• V= voltage (Measured in Volts)
• I= current (Measured in Amperes)
• R= resistance (Measured in Ohms)
• P= power (Measured in Watts)

Ohm's Law $V=I*R$

The definition of resistance requires us to regard it as a derived quantity. Resistance is associated with particular objects and not materials. For any device, we 'supply' a electric potential difference (voltage) and a current, and take the ratio of these two measured quantities to find resistance, as per 'Ohm's Law'. The elementary case of this law states that the relation is linear for all values of voltage and current, but this is not true. At high temperatures (generally, non-standard conditions) the linearity breaks down, in loose analogy to yield strength of a solid (continuum).

Power Law $P=V*I$
$P=(I^2)*R$
$P=(V^2)/R$

• note 2 values must be given to find unknown