1. ExamI coming up Feb 24th!(a week from TODAY) 5 multi-choice 10 pts/each TEST FORMAT? At least 1 (maybe 2) bonus multi-choice 5 pts/each (one may be a HW problem!) 2 written problems (partial credit!) 25 pts/each Cheat Sheet! Sample on web site: you’ll get one with the test HW3 due on Friday: P.S. or Review?

3. I = 2800 A (!) 4 cm V = ?

4. Real vs. idealized electric circuit (next)

5. Real electric circuit V = + 1.50 V 2 ft I Resister R = 220.0000 W 22 AWG wire Diameter = 0.025 in R/L = 0.0161 W/ft Define V = 0 here ! 3 ft

6. Idealized electric circuit (perfect wires) Perfect wires! (R = 0) V = + 1.50 V I R = 220.0000 W V = 0 V VR = I =

7. Real electric circuit V = + 1.50 V RW2 = 2 ft + R = 220.0000 W 22 AWG wire Diameter = 0.025 in R/L = 0.0161 W/ft Define V = 0 here ! 3 ft RW3 = Assume RT = RW2+R + RW3 = THEN I = V/RT

8. Real electric circuit V = + 1.50 V RW2 = 0.0322 W VW2=I RW2 = + VR=I R = 220.0000 W VW3=I RW3 = Define V = 0 here ! RW3 = 0.0483 W

9. But, What’s the voltage drop along a 100 ft long cable (18 AWG) when it’s carrying 20 A? (18 AWG: 0.00639 W/ft)

10. Voltage drop along wires! (18 AWG: 0.00639 W/ft) 20 A 110 V 20 A 100 ft

11. Electric Power

12. Electric Power But I is the same throughout the circuit!

14. I constant → HEAT! power lost as heat

15. Electric Power I V Units?

16. Electric Power If R is not to burn up. It must be able to dissipate heat at a rate of V×I

17. FROM the Basics You can derive ….

19. Lame resistor demo Example: Big guy is rated as 10  with max current of 6.5 Amps. What is the max power rating? Max voltage across it? Less-Lame fuse demo

20. Example: 18.30 A 115-V fish-tank heater is rated at 110 W. Calculate a) the current through the heater when it’s operating, and b) its resistance.