Ohm’s Law

Ohm’s Law Ohm’s Law states that the voltage v across a resistor is directly proportional to the current flowing through it

Resistance The resistance R of an element denotes its ability to resist the flow of electric current, measured in ohms (). 1 ohm = 1 volt / ampere

Resistance (cont.) A short circuit is a circuit element with resistance approaching zero. R = 0, short circuit: v = iR = 0 An open circuit is a circuit element with resistance approaching infinity. R = ∞, open circuit:

Conductance A useful quantity in circuit analysis is the reciprocal of resistance R, known as conductance G. Conductance is a measure of how well an element will conduct electric current, measured in mhos, or siemens (S).

Power Using Ohm’s Law and therefore, Power in terms of R: Power in terms of G:

Notes on Power The power dissipated in a resistor is a nonlinear function of either current or voltage. Since R and G are positive quantities, the power dissipated in a resistor is always positive. This means that a resistor always absorbs power from the circuit.

Examples An electric iron draws 2 A at 120 V. Find its resistance.

Examples How much current is drawn by a toaster with resistance 12 Ω at 110 V?

Examples In the circuit below, calculate the current i, the conductance G, and the power p.

Examples Calculate the voltage v, the conductance G, and the power p.