1. Do Now: An appliance uses 450 kJ of energy over 1 hour when connected with a p.d. of 120-V. What is the resistance of the appliance?
W = V2t/R
R = V2t/E
R = (120V)2(3600 s) / 450x103 J
115 W.

3. Sketching with Circuit Symbols
To represent components on circuit use symbols. See ref tables

4. Circuit Symbols

5. 1. Use your tables to sketch the circuit below with the appropriate symbols

6. 2 Types of Circuits
Series – single pathway for current flow. Components connected in succession like a chain.
Parallel – pathway with more than 1 branch – wire splits.

7. Ohm’s Law on Electric Circuits
Each component on a circuit has its own current, voltage, resistance.
Use Ohm’s Law for individual components: I1 = V1/R1 V1 = I1R1 or R1 = V1/I1
To analyze total current, voltage resistance for the entire circuit.
Itot = Vtot/Req
Vtot = ItotReq
Req = Vtot/Itot

8. The power supply (battery) provides the total E, the components may share (divide) the total E (p.d.), current, or both.

9. Analyzing Series Circuits Series circuits are a chain of components connected in a circle. Charges have 1 path. I1 = I2 = I3 = I4 … Conservation of Charge

10. 2. the reading on ammeter 1 is 3-A, what is the reading on ammeter 4?1. 4. 2. 3.

11. Resistance As more resistors are added in a series connection, the total equivalent resistance of the circuit increases. equivalent resistance is the simple addition of each resistor on the circuit. R1 + R2+ R3 = Req.

12. What is the equivalent resistance?
3. Given the circuit:
2-W.
4-W.
6-W.
What is the equivalent resistance?

13. Voltage on a series circuit
Voltage on a series circuit. The battery, or generator or source provides the Vtot for the circuit. The Vtot is the addition of each p.d. across each resistor on the circuit. V1 + V2+ V3 ~ Vtot.= the battery voltage

14. What is the total circuit voltage? What is the battery voltage?
4. Given the circuit:
1-V.
2-V.
3-V.
What is the total circuit voltage?
What is the battery voltage? 6V

15. 5. The p.d. or V across each resistor can be found:
V1 = IR1. V2 = IR2. V3 = IR3.
If resistance on V3 is 3 W, and the current is 1 A, what is the voltage V3?
What is the current through bulb 1?
What will happen if one of the bulbs burns out?
V = IR = (3W)(1A) = 3V 1A

16. Since there is only one path for the charges to follow, if one conductor (resistor) is disconnected, the circuit is broken. The current flow stops. The bulbs go out.

17. Since the devices must share the voltage, as more are added the energy of the charges decreases. The bulbs become dimmer.

18. In Class tx pg 745 #4a, 4c. Read txt 730 – 739 do 739 #1, 2, 4, 5
For problem 1,2 above sketch the circuit along side of the calculations w proper symbols for problem solving.

19. Do Now: A 4 W and an 8 W resistor are connected in series to a 24-V cell.
a. Sketch the circuit.
b. Calculate the total current.
c. What is the pd around the 8 W resistor

20. Parallel Circuits

21. The current reaches a fork, can choose path.
What’s Different?
The current reaches a fork, can choose path.

22. Through which resistor does more charge flow? Why?

23. Sketching: Make rungs or branches.

24. Resistors all connected across the V , all V equal to the battery voltage.
V1 = V2 =V3 = Vtot
Current (I), charges reach a junction, they divide.
Itot in the circuit = S currents in each branch.
Itot = I1 + I2 + I3 …
Individual currents
I1 = V R1

25. Reciprocal Nature 1/Req = 1/R1 + 1/R2 + 1/R3 …
Req is the equivalent or total resistance.
As you add resistors, the Req goes down!
What happens to Itot as R added?
Itot = V/Req.
Itot goes up!

26. Parallel circuits offer more than one path for q, parts can be disconnected, q will flow through other branches.
What happens to brightness and power.
Which equation to use?
V constant. Peach = V2/R, V constant.
P depends on R only.
As R added ratio is constant. No change.
Brightness constant

27. Ex 1: A 9V battery is connected in series to 2 bulbs: 4W, & 2W.
A) Sketch the diagram with the proper symbols. Show real and conventional current flow direction. B) Find the equivalent or total resistance on the circuit. C) Find the total current in the circuit. D) What is the voltage in each branch? E) Find the current in each branch.

28. Ex 2: A 9V battery is connected in parallel to 2 bulbs: 4W, & 2W
Ex 2: A 9V battery is connected in parallel to 2 bulbs: 4W, & 2W. A) Sketch the diagram with the proper symbols. Show real and conventional current flow direction. B) Find the equivalent or total resistance on the circuit. C) Find the total current in the circuit. D) What is the voltage in each branch? E) Find the current in each branch.

29. F) Add the currents from each branch together
F) Add the currents from each branch together. How do they relate to the total current? G) Now add a 3 W bulb to the circuit. Recalculate the equivalent resistance. H) How does the new resistance on the circuit compare to the original? I) Recalculate the power of each bulb. J) What happened to the bulbs’ brightness when the 3W bulb was added?

30. Summery Series: Add resistors, total
Parallel: as you dd resistors, the total:
Itot goes down
Req goes up.
Indiv P/brightness decrease.
Highest R = bright/most P
Remove 1, others go out.
Less bulbs each is brighter.
Itot goes up.
Req goes down.
Indiv. P/ Brightness equal.
Lowest R = most P brightest.
Remove 1, others stay on same power/brightness

31. Hwk 1 Rev Book Read 125 – 129. Do 129 #49-57. Separate sheet.
Film clip
Hwk:Text pg 745 #2 - 5.
Sketch the circuits in #4, 5.

32. Do Now: Assume that all the resistors, the voltage sources, and wires are identical. Determine, without a calculation which circuit has the lowest Req (total resistance)? Explain. A. B. C. D.

33. Power = Brightness
The bulb brightness in each resistor is dependent on the power in each resistor.
P = VI P = I2R P = V2/R,
can calculate the power and deduce the brightness.

34. Which equation is more useful for:
Series?
Parallel?
P = I2R
P = V2 R

35. 2. 2 bulbs in series connected to 6V cell. R1 = 2W, R2 = 4 W
2. 2 bulbs in series connected to 6V cell. R1 = 2W, R2 = 4 W. Find the power in each. What is relative brightness? What if a 1 W is added in series? What happens to the brightness of the remaining bulbs?

36. Ex 3: 3 bulbs in parallel connected to 6V cell
Ex 3: 3 bulbs in parallel connected to 6V cell. R1 = 2W, R2 = 3 W, R3 = 4W. What is relative brightness ? What if a 10 W is added in parallel? What happens to the brightness of the remaining bulbs? What happens to the total current drawn?

37. Use of Meters

38. Ammeters measure current so circuit current must flow through meter.
Connect meter in series to measure current.
Sketch the circuit.

39. Ideal ammeter has zero resistance.
What do you think will happen if an ammeter is connected in parallel by accident?

40. Voltmeters measure p.d. across resistors so must be connected in parallel. Sketch the circuit.

41. 4. Sketch a parallel circuit with a battery and 2 resistors; r1 and r2.
Show one ammeter reading the total current, and another ammeter reading the current in r1. Show a voltmeter reading the battery voltage and another reading the voltage in r2.

42. Ideal voltmeter has infinite resistance.
What do you think will happen if a voltmeter is connected in series by accident?

43. Kirchoff’s Laws The current entering junction = current exiting
Kirchoff’s Laws The current entering junction = current exiting. Application of “conservation of charge”.

45. 5. If I1 = 7A, I2 = 5A. What is the current in I3?

46. What is the current and direction in the unknown wire?
150 in, 180 out,
30 in

47. Review Book: read 126 -129. Do 130 #51-53, 57-63, 72-80.

48. Fuses – appliances are rated for the power they can safely dissipate
Fuses – appliances are rated for the power they can safely dissipate. That implies a certain current & voltage (power). Fuses should be chosen to have a current rating a bit higher than the one for which the resistor is designed.

49. Should fuses and circuit breakers be connected in parallel or in series? Why?

50. If a 60 W bulb is connected to a 120 V source, the current is:. P = VI
If a 60 W bulb is connected to a 120 V source, the current is: P = VI I = P/V. I = J/s = 0.5 C/s .5A J/C Fuse should be ~ .6-1 A.