$P=VI=\frac{dw}{dq} \frac{dq}{dt}=\frac{dw}{dt}$ - Power can be consumed or delivered - Sources deliver power - Passive sign convention: any element that consumes power will have current enter the positive terminal of that element - Independent source is where the value is constant, so independent voltage source will always supply the same voltage to the circuit - Dependent source: has the value depend on a voltage or a current - Current passing through voltage source depends on the rest of the circuit, e.g Ohm's Law; vice versa for voltage passing through current source - Ohm's Law: $V=IR$ - Turning off a voltage source = replace it with a short wire, called a short circuit - Turning off a current source = replace it with an open wire, called an open circuit