1

Name: _____________________ Date: ________Period: ___________

Unit 9Series & Parallel CircuitsSeries & Parallel Circuits

(Filled In)

Essential Questions:

• Does adding resistors to a circuit always reduce current?

• Does adding more light bulbs to a circuit always make them

less bright?

Objectives

• Draw schematic circuit diagrams for resistors in series and in parallel

• Discuss how the total current is different for the same resistors in series vs. in parallel

• Calculate the total resistance for resistors in series vs. i ll l

Slide 2

in parallel

2

Vocabulary

• Series Circuit – A circuit where the current follows one path without branching

• Parallel Circuit – A circuit where the current from the battery branches one or more times.

Slide 3

1 light bulbVoltage drop across light bulb = -9VCurrent leaving the battery = 0.9A

Draw schematic below. Include voltmeter andInclude voltmeter and ammeter.

Slide 4

3

2 light bulbs in series (current doesn’t branch)Voltage drop across light bulb = -4.5VCurrent leaving the battery = 0.45A (decreases)

Draw schematic below. Include voltmeter andInclude voltmeter and ammeter.

Slide 5

Opening a switch in a series circuit stops current from flowing completely

Draw schematic below. Include voltmeter andInclude voltmeter and ammeter.

Slide 6

4

2 light bulbs in parallel (current branches)

1 light bulb is disconnected

Current leaving the battery is 0.9 A

Draw schematic below. Include voltmeter and ammeter.

Slide 7

2 light bulbs in parallel (current branches)

Voltage drop across each light bulb = -9V

Current leaving the battery increases to 1.80ADraw schematic below. Include voltmeter and ammeter.

Slide 8

5

Practice 1

Slide 9

Voltage across two resistors in parallel is the same. One end of each resistor is at 16V, and the other end is at 0V.

Voltage = 10 VR = 2 I = ?Use V = IR, Ohm’s Law

10 2

5

V RI

I

I A

Does current always increase when you add resistors to the circuit?

• More resistors in series reduces the current leaving the battery (total current)

• More resistors in parallel increases the current leaving the b tt

ALess current

Slide 10

battery

AMore current

6

Calculating total resistance of series and parallel circuit

• Series Resistors: RTotal = R1 + R2

R1 R2

• Parallel Resistors:

R

A

1 2

1 1 1

TotalR R R

Slide 11A

R1

R2

Practice: Calculate total resistance of series and parallel circuit

• Series Resistors: RTotal = R1 + R2

10 10

Calculate total resistance:

• Parallel Resistors:

A

1 2

1 1 1

TotalR R R

Slide 12A

10

10

Calculate total resistance:

7

Electric Power P = IV

• Power = Current x Voltage

• More power comes from more current for the same voltage

• To increase current in a circuit, reduce resistance!(f V IR)

Slide 13

(from V = IR)

Practice 2

V = 12 VI 0 60 A

Slide 14

P = IVMore power comes from more current for the same voltage

I = 0.60 AUse P = IV

(0.6 )(12 )

7.2

P IV A V

P W

8

Practice 3

Slide 15

Practice 3 – Answers (a) and (b)

Voltage across resistor = 12 VR = 10 I = ?U V IR Oh ’ L

12 10

1 2

V RI

I

I A

Slide 16

Use V = IR, Ohm’s Law 1.2I A

9

Practice 3 – Answers (c)

R

Total current = 1.5 AHow much current goes through 10 Resistor? 1.2 A, found in (b)

Thus, the rest of the 1.5 A must be going

Slide 17

through the light bulb = 1.5A – 1.2 A = 0.3 A

12 0.3

40

V RI

R

R

Voltage across light bulb = 12 VI = 0.3AR = ?Use V = IR, Ohm’s Law

Practice 3 – Answers (d)

R

Light bulb and resistor in series looks like this:

Slide 18

In series, the total resistance of the circuit increases.Thus, the total current leaving the battery decreases.

10

Practice 4

Slide 19

Practice 4 - Answers

W

X

Y Z

S1

S2 F1

S1F1

Slide 20

11

Practice 5

Slide 21

Practice 5Answer (a)

a) I = ?V=20V

Switch connected to X makes this circuit

Two 5 resistors in series

R = 5 + 5 = 10

20 10

2

V RI

I

I A

Slide 22

12

Practice 5Answer (b)

b) I = 2 AV=20V

Switch connected to X makes this circuit

Two 5 resistors in series

(2 )(20 ) 40P IV A V W

Slide 23

Practice 5Answer (c)

Switch connected c) Placing the fuse at T will protect the circuit regardless

to Y and passes the current through U

12 and 5resistors in series

protect the circuit regardless of which point the switch connects to.If the fuse is at U, the fuse will only protect the circuit when switch is connected to Y.

Slide 24

13

Practice 5Answer (d)

c) The most warmth is generated by the largest

Switch connected to W

3 and 3resistors in series

generated by the largest current (P = IV).The smallest total resistance is when the switch is connected to W.Smallest resistance generates the largest current.

Slide 25

Practice 6

V = 12 VI = 5 AUse P = IV

(5 )(12 )

60

P IV A V

P W

Slide 26

In series, resistors add like this RTotal = R1 + R2

Removing one resistors reduces the total resistance and increases current. 10 10

A

V = 120 VI = 1.5 AUse P = IV

(1.5 )(120 )

180

P IV A V

P W