2. Unit 4 Electric Potential, Current, and Resistance

3. If charges A & B were allowed to move, in what direction would they move because of the electric field? Ignore the interactions between charge A & B

4. What do these images have in common?

6. Electrical Potential Energy (In a uniform electric field)

7. Potential Difference

8. Question? What’s the purpose of defining a new term “potential difference”, when in the past, “potential energy” would suffice?

9. Let’s try a problem… A charge moves a distance of 2.0 cm in the direction of a uniform electric field whose magnitude is 215 N/C. As the charge moves, its electrical potential energy decreases by 6.9 x 10 -19 J. A. Find the charge on the moving object. B. What is the potential difference between these two points? C. Do a unit analysis on the potential difference.

10. Potential & Candle Flames http://www.youtube.com/watch?v=a7_8Gc_Llr8

11. Practice A Problems 1-3

13. Current I

14. Current & Moving Charge Create a list of as many items as you can that involve current (moving charges).

15. Practice C Problems 1-5

16. Conceptual Challenges pg. 611 Why it matters…..

17. Bell Work A. In your own words, why do electrons want travel from the negative terminal of a battery to the positive terminal when they are connected? B. Similarly, when lightning hits the ground around you, it would go up one leg and out the other, whereas if you stood on one leg, it wouldn’t travel inside you. How does the lightning know where it can travel?

18. Resistance Definition: The opposition presented to electric current by a material or device. 4 Factors: Length Cross Sectional Area Material Temperature

20. Material (ρ) Material Resistivity(ohmmeter) Silver 1.59 x 10 -8 Copper 1.7 x 10 -8 Gold 2.4 x 10 -8 Aluminum 2.8 x 10 -8 Tungsten 5.6 x 10 -8 Iron 10 x 10 -8 Platinum 11 x 10 -8 Lead 22 x 10 -8 Nichrome 150 x 10 -8 Carbon 3.5 x 10 -5 Polystyrene 10 7 - 10 11 Polyethylene 10 8 - 10 9 Glass 10 10 - 10 14 Hard Rubber 10 13 Note: The quantity, “conductivity” is the inverse of a material’s “resistivity”.

22. Combining what we know so far…

23. Resistance Simulation http://phet.colorado.edu/sims/resistance-in-a-wire/resistance-in-a- wire_en.html