Chapter 11 Sections 1 and 2

The Math for Ohms Law along in DC Circuits

Ohm’s Law• Math in Action

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

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

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 = R1 + 4.34 k ohms = 4.7 k ohms + 4.34 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

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 + 1.82k ohms = 3.02k ohms