1. U3e-L3
Date
DRILL
Why are the + and – symbols unnecessary when drawing the DC power source in an electric schematic?
1. The length of the lines tell you which is positive and which is negative

2. U3e-L3
Drill (cont’d)
2. What is a schematic?
3. Circle the schematic.

3. (1 Schematic, 1 Table, 2 formulae, 2 calculations, 2 answers)
U3e-L3
Drill (cont’d) Joule’s Law & Ohm’s Law
P = V I & V = I R
4. An electric fan has a power of 600 W. The voltage is 120 v AC. What is
the current in this circuit? What is the resistance?
(1 Schematic, 1 Table, 2 formulae, 2 calculations, 2 answers)

4. Good use of electricity

5. Bad use of electricity

6. Direct Current (DC) V O L T A G E Schematic TIME symbol +12 V
1 sec. 2 secs. 3 secs. 4 secs.
Schematic
symbol
TIME

7. Alternating Current (AC)
1/60 SEC. V O L T A G E
+120 V
(1 cycle)
= Voltage
0 v
TIME
Schematic
symbol
-120 V
1/60 SEC.
“House current” is 60 cycles per second.

8. 1 cycle per 1/60 sec. = ? cycles per 1 sec.
FREQUENCY
On the graph of “house current” (AC) voltage over time you
can see that one complete cycle takes 1/60 sec. How many
cycles will be completed in 1 sec.?
1 cycle per 1/60 sec. = ? cycles per 1 sec.
60 cycles per sec.
The unit of measure for frequency of AC current is
Hertz (Hz)
1 cycle per second = 1 Hz
“House current” (from wall outlets) has a frequency of
60 cycles per second. Abbreviation is 60 Hz.

9. RESISTORS
Resistor: A material that opposes (resists) but does not block the flow of electrons.
SERIES RESISTORS
If the current in a circuit must pass through 1 resistor before
passing through the next resistor, the resistors are in SERIES.
Series: 2 or more things of the same type following each other in succession.
Schematic symbol
for resistor R3 R2 R1

10. RESISTANCE RT = R1 + R2 + R3……
Resistance: A measure of the degree to which a material opposes (resists) electron FLOW.
The total Resistance (RT) of resistors in series
is the sum of their values.
RT = R1 + R2 + R3……

11. RT = R1+ R2 + R3
RT = 1 Ω + 2 Ω + 3 Ω
RT = 6 Ω
R3 = 3Ω
R2 = 2Ω
R1 = 1Ω

12. Parallel Resistors
If the current in a circuit passes through 2 or more resistors
simultaneously, they are in parallel. R1 R2
Parallel: An arrangement that permits several tasks to
be completed simultaneously rather than
consecutively.

13. Calculate the RT for the circuit above
The total resistance (Rt) of resistors in parallel is:
1 =
Rt R1 R2 R3 ………
R1 = 5Ω
R2 = 4Ω
Calculate the RT for the circuit above

14. 1/Rt = 1/R1 + 1/R2
1/Rt = 1/5 Ω + 1/4 Ω
1/Rt = .2 Ω Ω
1/Rt = .45 Ω
1 = .45 Ω x Rt
1/.45 Ω = Rt
2.222 Ω = Rt

15. MIXED RESISTANCE
Series
Parallel

16. Total resistance in mixed circuits
Give a letter name to any parallel segments.
Solve each parallel segment.
Add the RT of the parallel segments to the R of
all of the resistors they are in series with.
R4 = 10Ω A
R3 = 5Ω
R2 = 4Ω
R1 = 2Ω
Parallel resistors are treated as a single resistor with a single value !!!

17. Solve the parallel segment first
1/RA = 1/R2 + 1/R3
1/RA = 1/4Ω + 1/5Ω
1/RA = .25Ω + .2Ω
1 = .45Ω x RA
1/.45Ω = RA
2.222Ω = RA A
R4 = 10Ω
R3 = 5Ω
R2 = 4Ω
RA = 2.222Ω
R1 = 2Ω
Parallel resistors are treated as a single resistor with a single value !!!

18. Then solve for the total resistance (Rt)
RT = R1+ RA + R4
RT = 2 Ω Ω + 10 Ω
RT = Ω
R4 = 10Ω A
R3 = 5Ω
R2 = 4Ω
RA = 2.222Ω
R1 = 2Ω
Parallel resistors are treated as a single resistor with a single value !!!

19. HOMEWORK R5=10Ω R6=8Ω What is the power of this circuit?B
R6=8Ω
R4=5Ω
V = 12 v
R2=2Ω
R1=5Ω
I = ?
What is the power of this circuit?
1. Solve for RT
2. Solve for Current (I)
3. Solve for Power (P)
HOMEWORK

20. Do homework here