1. Current Electricity Applied Physics and Chemistry Circuits Lecture 2

2. Ohm's Law Resistance: slowing of current due to atomic structure Things that affect resistance:  Length: longer wire has more resistance  Area: smaller cross section has more resistance  Temperature: higher temperature has more resistance  Material: different materials have different resistance

3. Resistances of different materials Pt Fe Al Au Cu Ag Resistance Increases

4. Ohm's Law Relates potential, current and resistance V = I R Resistance measured in Ohms ( Ω ) 1 Ω = 1 Js/C 2 V measured in Volts (V) 1 V = 1 J/C Current measured in Amps (A) 1 A = 1 C/s

5. Ohm's Law Many typical metals and circuit components obey Ohm's Law Some materials (like transistors and diodes) do not (non-Ohmic)

6. Ohm's Law A 30 V battery is connected to a 10 Ω resistor. What is the current through the circuit? Known: V=30V R=10 Ω Equation: V=IR or I=V/R I=30V/10Ω so I=3A

7. Ohm’s Law What is the current through a 30 Ω resistance that has a potential difference of 120 V? What we know: R = 30 ΩV = 120 V Equation: V = IR so I = V/R Substitute: I = (120V)/(30 Ω) Solve! I = 4A