1. SCI 340 L43 circuits
Group Work
Which has the greater resistance: a 75-W light bulb or a 100-W light bulb?
Bear in mind the formula P = VI.
At a given voltage, which dissipates more power?
Which must draw more current?
Bear in mind Ohm’s law I = V/R.
At a given voltage, which presents the greater resistance?

2. DC Circuits
Current and energy

3. Objective
Analyze the flow of current in simple, series, and parallel circuits.

4. Series Circuit Same I through each:
V = IR1 + IR2 + IR3 = I (R1 + R2 + R3)
Circuit resistance = R1 + R2 + R3

5. Series Summary The same current flows through all resistors in series.
The series resistance is the sum of the resistors’ resistances.
The resistors’ voltages add up to the series total.
The voltage across a resistor is proportional to its resistance.

6. Group Question
A 100-W bulb and a 75-W bulb are wired in series. Which dissipates the greater power?
The 100-W bulb.
The 75-W bulb.
Both dissipate the same power.
It is impossible to determine from what we have learned so far.

7. Parallel Circuit Diagram

8. Potential Differences

9. Currents Total current = I = I1 + I2 + I3 = V/R1 + V/R2 + V/R3
Circuit resistance =V/I =
1/R1 + 1/R2 + 1/R3 1

10. Parallel Summary
The same voltage drops across all resistors in parallel.
The total current is the sum of the resistors’ currents.
The effective circuit resistance is less than for any individual resistor.
Formula is
1/R = Si 1/Ri

11. Group Question
A 100-W bulb and a 75-W bulb are wired in parallel. Which dissipates the greater power?
The 100-W bulb.
The 75-W bulb.
Both dissipate the same power.
It is impossible to determine from what we have learned so far.

12. Series + Parallel Circuit
1/R2 + 1/R3 1
Circuit resistance = R1 +

13. Group Work
Determine current direction, current, voltage, and power for each resistor in each circuit.
12 W
6 W
9 W
18 W
9 W
8 W
10 W