1. Ohm’s Law

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

3. 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

4. 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:

5. 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).

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

7. 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.

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

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

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

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