1. View Vow How many electrons go past a point every second in a wire if the current is 12 Amps?

2. Objectives Understand that current tells us how much charge (think moving electrons! – but more to come on this) moves past a certain point every second. We all know “Resistance is futile”…but what is resistance when we are talking about Current?

3. Homework Castle Learning – Current and Resistance

4. Test Corrections today post and tomorrow. I do have a meeting today but I will be in here so feel free to come today for corrections. Please look over, ask questions, check the scoring and then return to your mailbox.

5. Worksheet Current

6. 4.2.2 Electrical Resistance Electrical Stopping Power

7. Definitions resistance: OPPOSITION TO CURRENT unit: Ω factors that change resistance: resistivity: MATERIAL length cross-sectional area temperature

8. R A Resistance Factors R ρ R L R Temp. NEXT

9. R A Resistance Factors R ρ R L R Temp. To build an “ideal” conductor with the smallest possible resistance you would select one that is: LOW RESISTIVITY, SHORT, WIDE, COLD

10. Determine the resistance of a 1.0 meter long copper wire with a cross-sectional area of 0.01 meter 2. Example #1 R = ρL / A R = (1.72 x 10 -8 Ω·m)(1.0 m) / (0.01 m 2 ) R = 1.72 x 10 -6 Ω

11. A piece of wire that has a length of 5.0 x 10 7 meters and a cross-sectional area of 0.025 meter 2 has a resistance of 31.8 ohms. –What is the composition of this wire? Example #2 R = ρL / A ρ = RA / L ρ = (31.8 Ω)(0.025 m 2 ) / (5.0 x 10 7 m) ρ = 1.59 x 10 -8 Ω·m

12. End of 4.2.2 - PRACTICE