Circuits. Ch. 35 in your text book

Transcription

1 Circuits Ch. 35 in your text book Objectives Students will be able to: 1) Draw schematic symbols for electrical circuit components 2) Calculate the equivalent resistance for a series circuit 3) Calculate the equivalent resistance for a parallel circuit

2 Electrical Schematic Symbols Wire Capacitor Resistor + - Battery Switch

3 Circuits Circuit - path or trip around something In order for a circuit to be created, electrons must have a complete path that lets them return to their starting point. What happens when a water pipe is disconnected or if an oil pipe gets broken? What happens if there is an unattached wire in a circuit? Unlike fluids, electrons will only flow if they have a complete loop in which to travel

4 Circuits Open Circuit circuit that does not make a complete loop + - Closed Circuit circuit that does make a complete loop Short circuit a circuit that has an unintended path through which all the current flows short

5 Example: Circuits

6 Circuits Time for the circuits lab

7 Circuits How can you tell if a circuit is wired in parallel or series? Parallel Series

8 Series Circuits Voltage and Current: Waterfall Analogy 9V Resistors 0 V

9 9V Series Circuits V T = V 1 + V 2 + V 3 + -Voltage is like how much gravitational potential energy the water has -Voltage across each of the resistors has to add up to the voltage of the battery 0 V

10 9V 0 V Series Circuits I T = I 1 = I 2 = I 3 = - Current is how much water is flowing through over the waterfall - In a series circuit, the current will be the same through everything in the path (only 1 path)

11 Series Circuits Equivalent resistance value of a single resistor that would take the place of all the resistors in a circuit R 1 R 2 R 1,

12 Series Circuits For the circuit with two bulbs, use the battery voltage and the current you measured to figure out the equivalent resistance of your circuit. V = IR What do you notice about the equivalent resistance of your circuit compared to the resistance of the individual bulbs? R T = R 1 + R 2 + R 3 +

13 Series Circuits What is the equivalent resistance for the following circuit? 3Ω 3Ω 3Ω R T = R 1 + R 2 + R 3 + R T = = 9Ω

14 Series Circuits What is the equivalent resistance for the following circuit? 6 Ω 4 Ω 8 Ω R T = R 1 + R 2 + R 3 + R T = = 18 Ω

15 Series Circuits Use the battery voltage and the equivalent resistance to find the current for the following circuit? 3Ω 3Ω 3Ω V T = I T R T 9 = I(9) I = 1 A How much current is running through each resistor?

16 Series Circuits Summary of the rules for series circuits: The voltages across each of the resistors have to add up to the total voltage of the battery V T = V 1 + V 2 + V 3 + The current will be the same through each resistor in series I T = I 1 = I 2 = I 3 = The sum of each resistor yields the equivalent resistance R T = R 1 + R 2 + R 3 +

17 Series Circuits Use the battery voltage and the equivalent resistance to find the current for the following circuit? 6 Ω 4 Ω 8 Ω V = IR 9 = I(18) I =.5 A How much current is running through each resistor?

18 Series Circuits Use the current and resistance for each resistor to find the voltage across each resistor? 6 Ω 4 Ω 8 Ω V = IR I 1 = I 2 = I 3 =.5A V 1 = (.5)(8) = 4V V 2 = (.5)(4) = 2V V 3 = (.5)(6) = 3V

19 Series Circuits Find the current for the circuit and then find the voltage across each resistor. 1 Ω 2 Ω 3 Ω V = IR V 1 = (1.5)(3) 9 = I(6) V 2 = (1.5)(2) I = 1.5 A V 3 = (1.5)(1)

20 9V Parallel Circuits V T = V 1 = V 2 = V 3 = 0 V -Voltage is like how much gravitational potential energy the water has. Each water fall had equal amount of potential energy -Voltage across each level parallel to the battery has the same voltage as the battery

21 Parallel Circuits 9V 0 V - Current is how much water is flowing through over the waterfall - Each waterfall can have a different current, but they are fed by the same river

22 Parallel Circuits I T = I 1 + I 2 + I 3 + I T =? 9V 3 A 3 A 3 A 3 A 0 V The current gets split before it goes over the fall. Similarly, the current in the circuit gets split between each resistor.

23 Parallel Circuits Equivalent resistance value of a single resistor that would take the place of all the resistors in a circuit R 2 R 1,2 R The resistors add up inversely:... R R R R T 1 2 3

24 Parallel Circuits Summary of the rules for parallel circuits: The voltages across each of the levels is the same as the battery V T = V 1 = V 2 = V 3 = The current at each levels adds to make the total current I T = I 1 + I 2 + I 3 +

25 Parallel Circuits Calculate the current going through each resistor V T = V 1 = V 2 = V 3 = 9V 9 = I(1) 9 = I(2) 9 = I(3) I = 9 A I = 4.5 A I = 3 A 1 Ω 2 Ω 3 Ω What is the total current coming out of the battery?

26 Parallel Circuits 1 Ω 2 Ω 3 Ω

27 Parallel Circuits Calculate the current going through each resistor V T = V 1 = V 2 = V 3 = 9V 9 = I(6) 9 = I(4) 9 = I(8) I = 1.5 A I = 2.25 A I = A 6 Ω 4 Ω 8 Ω What is the total current coming out of the battery?

28 Parallel Circuits 1 R T = = Ω 4 Ω 8 Ω R T R T = 1/.542 = 1.85 Ω

29 Compound Circuits 9V A compound circuit has a mix of series and parallel wiring 0 V

30 Compound Circuits Step 1: Combine the resistors that are in series or parallel R 3 R R 1 1 R 2,3 Example 1: R V R 2,3 R 2 R 3 Example 2: R 1 R

31 Compound Circuits Step 2: Combine the resistors that are in series or parallel Example 1: R 1 R 2,3 R 1,2, V + - R 2,3 R 1,2,3 Example 2: R

32 Compound Circuits What will the equivalent resistance be when you combine R2 and R3? R 1 = 3Ω R 3 = 3Ω R 2 = 3Ω R 1 = 3Ω R 2,3 =? + - R T = 1/3 + 1/3 = 2/3 =.67 R 2,3 = 1/.67 = 1.5 Ω

33 Compound Circuits R 1 = 3Ω + - R 2,3 = 1.5 Ω What is the current running through each resistor? V = IR 9 = I(4.5) I = 2 A R 1 R 2 R 3 Voltage 6 V 3 V 3 V Current 2 A Remember, this is a combination of two resistors How much voltage is used on each resistor? V 1 = (2)(3) = 6 V V 2,3 = (2)(1.5) = 3 V

34 R 1 = 3Ω R 3 = 3Ω R 2 = 3Ω Compound Circuits How much voltage is used on each resistor? R 2 and R 3 are in parallel with each other so they have the same voltage, 3 V + R 1 R 2 R 3 Voltage 6 V 3 V 3 V Current 2 A 1 A 1 A - What is the current running through each resistor? V = IR 3 = I 2 (3) 3 = I 3 (3) I 2 = 1 A I 3 = 1 A

35 Compound Circuits What will the equivalent resistance be when you combine R2 and R3? R 2 = 3Ω R 3 = 3Ω R 2,3 = 6Ω R 1 = 3Ω R 1 = 3Ω

36 Compound Circuits + - Voltage Current R 2,3 = 6Ω R 1 = 3Ω R 1 R 2 R 3 What is the voltage across each resistor? V 1 = 9V V 2,3 = 9V Remember, this is a combination of two resistors

37 Compound Circuits + - R 2,3 = 6Ω R 1 = 3Ω R 1 R 2 R 3 Voltage Current 3 A 1.5 A 1.5 A What is the current running through each resistor? V = IR 9 = I 1 (3) I 1 = 3 A 9 = I 2,3 (6) I 2,3 = 1.5 A Remember, these two are in series

38 Compound Circuits R 2 = 3Ω R 1 = 3Ω R 3 = 3Ω What is the voltage across R 2 and R 3? V 2 = (1.5)(3) = 4.5 V V 3 = (1.5)(3) = 4.5 V + - R 1 R 2 R 3 Voltage 4.5 V 4.5 V Current 3 A 1 A 1 A

39 Compound Circuits R 1 = 3Ω R 3 = 3Ω R 2 = 3Ω R 1 = 3 Ω R 2,3 = 1.5 Ω + - 1) Current 2) Voltage 3) Current + -

40 Compound Circuits R 2 = 3Ω R 1 = 3Ω R 3 = 3Ω R 2,3 = 6Ω R 1 = 3Ω 1) Voltage 2) Current 3) Voltage

41 Summary of Rules Parallel: V T = V 1 = V 2 = V 3 = I T = I 1 + I 2 + I 3 + Series: V T = V 1 + V 2 + V 3 + I T = I 1 = I 2 = I 3 = R T = R 1 + R 2 + R 3 +

42 To Finish Up In your notes, answer the following questions. 1. Draw the symbol for a battery, resistor, wire, capacitor, and a switch 2. Calculate equivalent resistance in a series and parallel circuit 3. Calculate the voltage and current for resistors in a series and parallel circuit