Physics

Physics

Chapter 20:

Circuits and Circuit Elements


SchematicDiagram of an Electric CircuitUses Symbols to Represent Elements within

the Circuit

+ -

R1R2


SchematicsSome Standard Symbols

Conductor

Switch

Fuse



Capacitor

Resistor

Potentiometer



Ground

Battery

Generator + -

+ -



Connection

No Connection


Series Wiring

+ -

R1R2


Series WiringMore than One Device Connected to a Voltage

SourceProvides the Same Electric Current Through

Each Device


Series WiringCurrent Flow Interrupted at One Device Will

Prevent Current from Reaching the Other Device

+ -

R1R2

I


Series WiringThe Voltage Supplied by the Power Source is

Divided Among the Devices Used in the Circuit

+ -

R1R2

I

V1V2...21 VVV


Series WiringThe Resistance to the Circuit Voltage is the

Sum of the Device ResistanceEquivalent Resistance in Series (Rs)

+ -

R1R2

I

V1V2...21 RRRs


Series WiringSo…

sIRV

+ -

R1R2

I

V1V2

and

RIP 2


Parallel Wiring

+ -

R1

R2


Parallel WiringMore than One Device Connected to a Voltage

SourceProvides the Same Electric Voltage Through

Each Device


Parallel WiringCurrent Flow Interrupted at One Device Will

NOT Prevent Current from Reaching the Other Device

+ -

R1

R2

I1

I2

I


Parallel WiringVoltage is the Same at Each ResistorCurrent is Divided Among the Devices Present

in the Circuit

+ -

R1

R2

I1

I2

I


Parallel WiringSince I=V/R and

Voltage is Constant

...111

21 RRRp

+ -

R1

R2

I1

I2

I

...21 III


Parallel WiringRp – Equivalent Resistance in Parallel

+ -

R1

R2

I1

I2

I

...21 III

...111

21 RRRp


Parallel WiringSo…

+ -

R1

R2

I1

I2

I

pRVI1


Problem: A current of 1.2 A is measured through a light

bulb when it is connected across a 120V source. What power is dissipated by the bulb?


Solution: V = 120V I = 1.2 A P = ?

WxAVVIP 2104.1)2.1)(120(


Problem: A 12V automobile battery is connected to an

electric starter motor. The current through the motor is 210A. How many joules of energy does the battery deliver to the motor each second, and what power, in watts, does the motor use?


Solution: V = 12V I = 210 A P = ?

sJxAVVIP /105.2)210)(12( 3


Problem: A flashlight bulb is connected across a 3.0V

potential difference. The current through the lamp is 1.5A. What is the power rating of the lamp, and how much electric energy does the lamp use in 11 minutes?


Solution: V = 3.0V I = 1.5 A P = ?

WAVVIP 5.4)5.1)(0.3(

Jxs

WPtEsot

EP 31097.2

min1

60

1

min11)5.4(,


Problem: What voltage is applied to a 4.0 resistor if the

current is 1.5 A?


Solution: I = 1.5 AR = 4.0V= ?

VAIRV 0.6)0.4)(5.1(


Problem: A voltage of 75V is placed across a 15

resistor. What is the current through the resistor?


Solution: R = 15.0V= 75V I = ?

AV

R

VI 0.5

0.15

75


Problem: The graph in shows

the current through a device called a silicon diode. A potential difference of +0.70 V is placed across the diode. What resistance would be calculated?


Solution: V = 0.70V I = 0.022AR = ?

32022.0

70.0

A

V

I

VR


Problem: Draw a series circuit diagram to include a

16 resistor, a battery, and an ammeter that reads 1.75 A. Conventional current is measured through the meter from left to right. Indicate the positive terminal and the voltage of the battery.


Solution: I = 1.75AR = 16V = ?

VAIRV 28)16)(75.1(


Problem: The wire in a house circuit is rated at 15.0 A

and has a resistance of 0.15 . What is its power rating?


Solution: I = 15.0AR = 0.15 P = ?

WRIP 34)15.0()0.15( 22


Problem: An electric motor operates a pump that

irrigates a farmer’s crop by pumping 10,000 L of water a vertical distance of 8.0 m into a field each hour. The motor has an operating resistance of 22.0 and is connected across a 110V source. What current does it draw, and how efficient is the motor?


Solution: V = 110VR = 22.0 I = ?

AV

R

VI 0.5

0.22

110


Solution: V = 110VR = 22.0 I = 5.0A

JxmsmkgxmgdEw524 108.7)0.8)(/8.9)(101(

JxsVAIVtEm61098.1)3600)(110)(0.5(

%391001098.1

108.7100

6

5

xJx

Jxx

E

EEff

m

w


HomeworkPages 755-756

Problems:17 (a, 24 b, 1.0A)19 (a, 2.99 b, 4.0A)26 (a, 1.7A b, 3.4V c, 5.1V d, 0.42A)

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