1. Resistance in a Complex Circuit
Ohm’s Law
Resistance in a Complex Circuit
Objective: To calculate the total resistance in series and parallel circuits in order to apply Ohm’s Law.
Energy Note: How do circuits differ from each other??
Drill: 1. Get a new lab from the SET.
2. Form groups.
3. Each group needs a materials tote and BOTH circuit boards.
4. Compare your homework diagrams.
5. Wait quietly for directions.
one
GTE-8B

2. Resistance in a Complex Circuit
Ohm’s Law
Resistance in a Complex Circuit
Objective: To calculate the total resistance in series and parallel circuits in order to apply Ohm’s Law.
Energy Note: How is the total resistance in a circuit calculated?
Drill: 1. Open your Log Book.
2. Come up with an analogy for current, voltage, and resistance. Thin about roads, pipes, rivers, etc…
one
GTE-8B

3. Resistance in a Complex Circuit
Ohm’s Law
Resistance in a Complex Circuit
Activity 1: Setting the Stage
If the resistance in a circuit is 12 ohms, and the voltage is 120 volts, what is the current? Show all work using proper form.
Current = Voltage ÷ Resistance
Current = 120V ÷ 12Ω
Current = 10A
Are all circuits this simple? Explain your thoughts.
one
GTE-8B

4. Resistance in a Complex Circuit
Ohm’s Law
Resistance in a Complex Circuit
Resistance in a Series Circuit
The resistance in a series circuit is equal to the sum of the individual resistors in the circuit. Why?
Every electron must pass through each resistor.
one
GTE-8B

5. Resistance in a Complex Circuit
Ohm’s Law
Resistance in a Complex Circuit
Example: If there are two 3 ohm resistors and one 4 ohm resistor in a series circuit, the total resistance equals _____ ohms.
  Ohms
Practice Problem: If a series circuit is powered by a 20 volt battery and there are two bulbs on the circuit, each with a resistance of 4 ohms, what is the current? (Calculate the total resistance first and then apply Ohm’s Law.)
one
GTE-8B

6. Resistance in a Complex Circuit
Ohm’s Law
Resistance in a Complex Circuit
Resistance = 4Ω + 4Ω = 8Ω
Current = Voltage ÷ Resistance
Current = 20 V ÷ 8Ω
Current = 2.5A
one
GTE-8B

7. Resistance in a Complex Circuit
Ohm’s Law
Resistance in a Complex Circuit
Activity 3: Resistance in a Parallel Circuit
In a parallel circuit, what happens to the resistance when branches are added?
The total resistance decreases.
one
GTE-8B

8. Resistance in a Complex Circuit
Ohm’s Law
Resistance in a Complex Circuit
Resistance in a Parallel Circuit
The reciprocal of the total resistance in a parallel circuit is equal to the sum of the reciprocals individual resistors in the circuit.
This is because all of the current does not have to go through each resistor.
one
GTE-8B

9. Resistance in a Complex Circuit
Ohm’s Law
Resistance in a Complex Circuit
Practice Problem: If a parallel circuit is powered by a 20 volt battery and there are two bulbs on the circuit, each with a resistance of 4 ohms, what is the current? (Calculate the total resistance first and then apply Ohm’s Law.)
one
GTE-8B

10. Resistance in a Complex Circuit
Ohm’s Law
Resistance in a Complex Circuit
Resistance = 4Ω + 4Ω = 4Ω
Resistance = 2Ω (reciprocal of 2/4)
Current = Voltage ÷ Resistance
Current = 20 V ÷ 2Ω
Current = 10A
one
GTE-8B

11. Resistance in a Complex Circuit
Ohm’s Law
Resistance in a Complex Circuit
Look at the answers to the two practice problems. What concept(s) is/are illustrated by the solutions?
When the same resistors are wired in series the total resistance is greater than that of the same resistors wired in parallel.
Therefore, the current in the parallel circuit is greater.
one
GTE-8B

12. Resistance in a Complex Circuit
Ohm’s Law
Resistance in a Complex Circuit
Class Practice
HOMEWORK: Self Practice
one
GTE-8B