The following relationships involve potential difference, current, power, and resistance, and can be used to solve problems involving these quantities, which may involve several steps.

$$ V=IR $$

$$ P=IV=I^2R=\dfrac{V^2}{R} $$

$$ R_T=R_1+R_2+... $$

$$ \dfrac{1}{R_T}=\dfrac{1}{R_1}+\dfrac{1}{R_2}+... $$

The following relationships can be used to solve problems involving potential divider circuits.

$$ V_1=[\dfrac{R_1}{R_1+R_2}]V_s $$

$$ \dfrac{V_1}{V_2}=\dfrac{R_1}{R_2} $$