electric circuits powerpoint

7/24/2019 Electric Circuits PowerPoint

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Electric Circuits

AP Physics B


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Potential Diference

=Voltage=EMFIn a battery, a series of chemical

reactions occur in whichelectrons are transferred fromone terminal to another. There isa potential difference (voltage)between these poles.

The maximum potentialdifference a power source canhave is called the electromotiveforce or (EMF), . The term isn't

actually a force, simply theamount of energy per charge(!" or #$


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A Basic CircuitAll electric circuits have three main parts

%. A source of energy

&. A closed path

. A device which uses the energy

If A) part of the circuit is open the device will not wor*+


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Electricity can be symbolic o

Fluids

"ircuits are very similar to water flowing through a pipe

A pump basically wor*s on T-IP-/TAT P/I"IP012 concerning its

flow3 There is a PRESSURE DIFFERENE

where the flow begins and ends3 A certain !M"UN#of flow passes each

SE"ND.

! circuit $a%icall& 'or% on #"

IMP"R#!N# PRINIP*ES3 There is a 4P"#EN#I!* DIFFERENE

aa +"*#!E4 from where the charge

begins to where it ends

3 TheThe !M"UN# of -!RE!M"UN# of -!REthat flowsthat flowsPER SE"NDPER SE"ND is calledis called URREN#.URREN#.


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Current"urrent is defined as the rate at which charge

flows through a surface.

The current is in the same direction as the flowof positive charge ("onventional "urrent$

ote5The 6I7 standsfor intensity


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There are ty!es o CurrentD / Direct urrent 8 current flows in one direction

Example0Battery

! / !lternating urrent8 current reverses direction many times per second.This suggests that A" devices turn -99 and

-. Example0all outlet (progress energy$


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"hm#s $a%

The voltage (potential difference, emf) is directlyrelated to the current, when the resistance is

constant

IR

IRV

RR

IV

=

=

==

Resistancealityproportionofconstant

2ince /:#!I, the resistance is the

20-P1of a # vs. I graph

R

/re%i%tan

ce/%lope


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&esistanceResistance (R); is defined as the restrictionof electron flow. It is due

to interactions that occur at the atomic scale. 9or eust slow them down a bit and cause the system to wasteenergy. Thin* of as bouncer at the 61lectric "lub7

#1e unit for re%i%tance i%t1e "-M,


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Electrical P"'E&e have already learned that P"ERis the rate at '1ic1 'or

(energ&) i% done. "ircuits are a prime e


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P"'E&It is interesting to see how certain electrical

variables can be used to get P-1/. 0et=sta*e #oltage and "urrent for e


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"ther useul !o%er ormulas

These formulas can also

be used+ They are

simply derivations of

the P-1/ formulawith different versions

of -hm's law

substituted in.


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Ways to Wire Circuits

There are & basic ways to wire a circuit. eep in

mind that a resistor could be A)TIC ( bulb,

toaster, ceramic material@etc$

2eries; -ne after another

Parallel; between a set of >unctions and

parallel to each other (provides multiplepaths for charge to travel$.


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(chematic (ymbolsBefore you begin to understand circuits you need to be able to

draw what they loo* li*e using a set of standard symbolsunderstood anywhere in the world

For t1e $atter& %&m$ol, t1e

*"N line i% con%idered to $e

t1e P"SI#I+E terminal and t1e

S-"R# line , NE!#I+E.

#1e +"*#ME#ERand !MME#ER

are %pecial device% &ou place IN

or !R"UNDt1e circuit to

mea%ure t1e +"*#!Eand

URREN#.


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The Voltmeter and AmmeterThe voltmeter and ammeter cannot be

>ust placed anywhere in the circuit. They

must be used according to their

?19IITI-.

2ince a voltmeter measures voltage or

P-T1TIA0 ?I991/1"1 it must be

placed !R"SSthe device you want to

measure. That way you can measure the

"AC1 on either side of the device.3Ammeter is placed in series3Voltmeter is placed in parallel

#oltmeter is drawn A"/-22 the resistor

2ince the ammeter measures the current or

90- it must be placed in such a way as the

charges go #-R"U-the device.

"urrent goes T/-DC the ammeter


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(im!le Circuit

When drawing a circuit itis wise to start by

drawing the battery

first, then follow alongthe loop (closed)

starting with positiveand drawing what you

see.


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(eries Circuit

In %erie%circuit, the resistors

are wired one after

anot1er. 2ince they are all

part of the 2A1 0--P

they each e


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(eries Circuit

321)(

321)(

VVVV

IIII

Totalseries

Totalseries

++=

===

As the current goes through the circuit, the charges must D21 11/C) to get through the

resistor. 2o each individual resistor will get its own individual potential difference. e call this

difference #-0TAC1 ?/-P(?ropE ?oes resistance always drop as charge passes through

a resistorE$

=++=

++=

=++=

is

series

seriesTT

Totalseries

RR

RRRR

RIRIRIRI

IRVVVVV

321

332211

321)(

)(

;ote5They may use the terms

6effective7 or 6eFuivalent7 to mean

T-TA0+


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E)am!le A series circuit is shown to the left.a$ hat is the total resistanceE

b$ hat is the total currentE

c$ hat is the current across 1A"resistorE

d$ hat is the voltage drop acrosseach resistorE( Apply -hm's law

to each resistor separately$

R(%erie%) / 2 3 4 3 5 / 6

+/IR 24/I(6) I / 4!

#1e& E!- get 4 amp%7 (I

i% con%tant i% %erie%777)

+2= 2) 1)= 4 + +5/(4)(5)/ 6+ +4/(4)(4)/ 8+

Notice t1at t1e individual +"*#!E DR"PS add up to t1e #"#!*77


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Parallel CircuitIn a parallel circuit, we have

multiple loops. 2o thecurrent splits up among theloops with the individualloop currents addingto thetotal current

It is important to understand that parallel

circuits will all have some position where

the current splits and comes bac*

together. e call these 9UN#I"NS.

The current going I to a >unction will

always eFual the current going -DT of a

>unction (irchhoff's 0aw$

9unction% OUTIN

Totalparallel

II

IIII

=

++=

:JunctionsRegarding

321)(


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Parallel Circuitotice that the D"TI-2 both touch theP-2TI#1 and 1CATI#1 terminals of the

battery. That means you have the 2A1

potential difference down 1A" individualbranch of the parallel circuit. This means

that the individual voltages drops are eFual.

This >unction

touches the

P"SI#I+E

terminal

This >unction

touches the

NE!#I+E

terminal

+

=

++=

++=

=++=

===

iP

P

Parallel

T

T

Totalparallel

Totalparallel

RR

RRRR

R

V

R

V

R

V

R

V

IRVIIII

VVVV

11

1111

)(

;

321

3

3

2

2

1

1

321)(

321)(


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E)am!le

===

++=

454.0

1454.0

1

91

1

511

P

p

P

RR

R

==

=

)(! RI

IRV

To the left is an e


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Com!ound *Com!le)+Circuitsany times you will have series and parallel in the 2A1 circuit.

2olve this type of circuit

from the inside out.

-!# IS #-E #"#!*

RESIS#!NE=

=+=

=+=

3.1133.33!0

3.33;50

1

100

11

s

P

P

R

RR


23/24

Com!ound *Com!le)+Circuits

=+=

=+=

3.1133.33!0

3.33;50

1

100

11

s

PP

R

RR

=

=

=

T

T

TTT

I

I

RIV

)3.113(120

2uppose the potential difference (voltage$ is eFual to 24:+. hat is the totalcurrentE

2.:6 !

hat is the #-0TAC1 ?/-P across the GHresistorE=

=

=

!0

!0

!0!0!0

)!0)(0".1(

V

V

RIV

;8.; +


24/24

Com!ound *Com!le)+Circuits

AI

VV

AI

VV

R

T

T

T

0".1

!.!4

0".1

120

3.113

!0

!0

=

=

=

=

=

=

+=+=

==

3#2

3#2

3#21)(

32)(

!.!4120

V

VVVV

VVV

seriesT

parallelT

hat is the #-0TAC1 ?/-P across

the %HHand HresistorE

5>.4 + Eac17 ==

==

==

+=

50

2.35

100

2.35

50

100

3#21)(

32)(

I

I

III

III

seriesT

parallelT

hat is the current across the

%HHand HresistorE

:.5>4 !

:.?:8 !

!dd to

2.:6!

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