1. The Math for Ohms Law along in DC Circuits
Chapter 11 Sections 1 and 2
The Math for Ohms Law along in DC Circuits

2. Ohm’s Law Math in Action Resistance in Series and Parallel Circuits
Read section to answer the following:
What do current limiting resistors do as part of an LED display board
How does Kirchhoff’s Voltage Law relate to this
Resistance in Series and Parallel Circuits
First Step Calculating Series resistance.
See Figure 11-1 on page 221
If the circuit has more than one resistor they are identified by a subscript on R and/or by values (if known)
For (a) RT = R , (b) RT = R1 + R2 (c) RT = R1 + R2 + R3
For (c) RT = R1 + R2 + R3 (d) RT = R1 + R2 + R3 + R4
Do Examples 11-1, 11-2, & 11-3

3. Ohm’s Law Resistance in Series and Parallel Circuits
Calculating Parallel resistance.
See Figure 11-2 on page 222
If the circuit has more two or more resistors in parallel they are identified by a subscript on R and/or by values (if known)
Conductance of a resistor = 1/R = G, R = 1/G
In a parallel circuit the total conductance equals a sum of all the parallel components
GT = G1 + G2 + G3 + …. + Gn
RT = 1/GT
Do Examples 11-4 and 11-5

4. Ohm’s Law Resistance in Series and Parallel Circuits
Calculating Series-Parallel resistance.
See Figure 11-3 on page 224
GT = G1 + G2 + G3 + …. + Gn
RT = R1 + R2||R3 = R1 + RX , RX = 1/GX
GX = G2 + G3 = 230uS  RX =4.34k ohms
RT = R k ohms = 4.7 k ohms k ohms
RT = 9.04 k ohms
See Figure 11-5 on page 224
RT = R1 + R2||R3|| R4 = R1 + RX
GX = 147uS + 100uS +303uS = 550uS
RX = 1/GX = 1/550uS = 1.82k ohms

5. Ohm’s Law Resistance in Series and Parallel Circuits
Calculating Series-Parallel resistance.
See Figure 11-5 on page 225
RT = R1 + RX = 1.2k ohms k ohms = 3.02k ohms