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Electric Charges Electric Charges

Electric Charges - PowerPoint Presentation

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Electric Charges - PPT Presentation

A little chemistry All matter Atoms are is m a de up of ato m s made of pr o ton s n e utr o ns a n d ele c tro n s ID: 270365

circuit current electric charge current circuit charge electric electrons voltage resistance path series branch bulb wire ent light circuits

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Slide1

Electric ChargesSlide2

A

little

chemistry

All

matter

Atoms

are

is m

a

de

up

of ato

m

s

made

of

pr

o

ton

s

,

neutrons, and electrons Protons: (+) Neutrons ( no charge ) Electrons: (-)

 Atoms can have a positive

charge,

a

negative charge, or no charge at all.Slide3

Charges

El

e

ctr

i

cal

charge

– caused by an

imb

a

lance of protons and ele

c

trons

Posit

i

ve

(

m

ore pro

t

ons

than

electrons)

 Negative (more electrons than protons) Neutral (same number of protons and (El

ectric Fields of

each sho

wn

above…) Opposites attractel

ectron

s)

Likes

repelSlide4

More

Chemistry

A

c

harge can n

e

ver be crea

t

ed

or destro

y

ed.

It is tran

s

fer

r

ed

f

r

om

o

n

e

ob

ject to another.This happensto anotherwhenelectronsmovefromon

eobjectOpposite

Charge

Like Char

geSlide5

Transferring

Char

g

e

Electric

e

n

er

g

y

is

n

ever cre

ated

or de

s

tro

y

e

d

,

o

n

ly

tra

n

sferredObje

cts (generally those that arecan become charged by one of 31. Induction2. Conduction3. Frictioncond

uctors)ways:Slide6

Transferring

Char

g

e

Ind

u

cti

o

n

– Tra

n

sfer

r

ing a ch

a

rge

by

bri

n

ging

a

c

h

ar

g

ed

object NEAR a neutral

object withouttouching it.The total charge on the door knob will still be neutral, but the opposit

e sides will have opposite chargesSlide7

Transferring

Char

g

es

Conduction

- Electr

o

ns

are

t

ra

nsferr

ed

from

o

n

e

o

b

ject

to an

o

ther

by contact, or touching.

When a negatively charged rod touches a neutral door knob, electrons transfer from the rod to the door

knob to give the doork

nob a negative

chargeSlide8

Transferring

Char

g

e

Fricti

o

n

- two

o

b

jects

rub

up

a

g

ain

s

t

e

a

ch

other,

lea

v

ing electrons built up

on one side. Bothobjects become charged.i.e. rubbing a balloon on your head, walking acrosscarpet

, wool rubbing on metal…

Slide9

Static

Dischar

g

e

J

o

hn

T

r

a

vo

l

t

a

ge!!

ht

t

p:

/

/

p

het.

c

olorado.edu/en

/simulation/travoltageSlide10

Con

t

ro

l

li

n

g

the Path

of

Elec

t

ric Cha

r

geElect

r

ical

Conducto

r

:

a

m

ateri

a

l

in which

charges mo

ve freelyi.e. metal (wires) and waterElectrical Insulator: a material in whichcharg

es cannot move freely

i.e. plastic,

wood,

glass, foam, cloth, ceramicSlide11

Con

t

ro

l

li

n

g

the Path

of

Elec

t

ric

Cha

r

ge

El

e

ct

r

ical

Con

d

ucto

r

:

t

h

e

metal i

nside the cord presentsapath of little resistancecharge to flowfor the

Electrical Insulator:

the r

ubber/pl

astic has a highresistance, to keep the charge

from leaving

th

e m

etal p

ath

of

wire

(and

to

ensu

r

e

you don

t

shock

your

s

e

l

f

when

you

tou

c

h

the

cord

!

)Slide12

CURRENTS

AND OHM’S

LAWSlide13

What?

Elec

tricit

y – flow

of electric current

Electric

current

the

mo

vem

ent

of

a

n

e

l

ectr

i

cal

c

har

g

e

.

In most cases,

wethink of an electric current running through a circuit. In comes Ohm’s Law.Slide14

Ohm’s

Law

V

= I x R

V =

V

o

l

t

a

g

e

(

units are vol

t

s

,

v)

I

= Curr

e

nt

(

units are

ampre

s

, A)R = Resistance (units are ohms,

Ω)Slide15

Voltage

V

olt

age is the

difference in

betwee

n two places

where

A neg

ative

char

ge

(elect

ron)

from other n

e

g

ati

v

e

c

ha

r

g

es

el

e

ctrical

potentialelectrons are flowing

.wants to move away(other electrons.) These repulsive forces increase as electrons are closer

toeach other. Electrons

flow from

high potent

ial energy to low potential. This po

tential

diffe

ren

ce is

usually

just

cal

l

ed

v

ol

t

a

g

e

V

olt

a

g

e

p

r

ovi

d

es

the

e

ne

r

g

y

that

pu

s

hes

a

nd

pulls

el

e

ct

r

ons

th

r

ou

g

h

the

cir

c

uit.

V

o

l

ta

g

e

is measur

e

d

in

V

olts

(V)Slide16

Batteries

Batteries

can ha

v

e diff

e

rentvo

ltage

, and there

fore push

diff

erent strength

curre

nts R

an

g

e

f

r

om

1

.

5

v

o

l

ts

to 12 volts Batteries ha

ve a positive terminaland a negative terminal. Electrons are pushed from the negative terminal and are pull

ed towards the positive ter

minal BUT

current

is in the opposite directionSlide17

Voltage

B

a

sically…

Voltag

e is diff

erence motio

n

Voltage

is

p

otential

e

lectrical

that

sets

a

c

har

g

e

in

the

PUSH

and

is measured

in Volts (V)Slide18

Current:

General

Idea

An object

moving in

a specific direction

Current

can be w

ate

r,

air

,

cars,

o

r

c

ha

r

g

e

Current

is

caused because of a difference pressure

on either side of an objectin Once the difference in pressure is gone

, current stops Pumps & B

atteries are

used to

maintain a difference inpressure.Slide19

Electric

Current

Just as

w

ater cu

rrent is fl

ow of w

ater molecules,

electri

c curr

ent is the

flow of

elec

tric charge

.

M

e

a

s

ur

e

d

in

A

mpe

r

es (A) In met

al circuits, movingflow of charge. Electrons travelnegative to positive Current t

ravels inelectrons

make

up

thethe OPPOSITEas electrons do.

di

re

ctionSlide20

Types

of Current

THERE

ARE T

WO TYPES

OF CURRENT:

In

a di

rect

curr

ent

(DC)

the curre

nt

always moves

te

r

minal

to the o

t

her in the sa

m

e

direction.

-

e

x

ample: battery

fromoneIn an alternating current (AC) the current willalways alternate directions at regular i

ntervals.- example:

appliances at h

ome

Remember, direction of the cur

rent

is

op

po

site

the

d

ir

e

ction

o

f

ele

c

t

r

on

fl

o

w

.Slide21

V

olta

g

e

and

Cur

r

ent

V

o

l

ta

g

e

PUSHES c

har

g

es th

r

ough

ci

r

cuit

s

.

Current

is how fast electr

ons FLOW thru the Example – you could say that…circuit Amps meas

ure how much water

comes out

of

a hose. Volts measure how

ha

rd

the

wate

r

ho

s

e

.

c

o

mes

out

of

a

Basi

c

ally:

As

V

o

l

ta

g

e Inc

r

ease

s

,

Current

Incr

e

ases!Slide22

Practi

c

e!

So

how does

this relate to a

wesome computer si

mulations?

ht

tp://p

het.color

ado

.edu/en/s

im

ulat

ion/ohms-lawSlide23

Resis

t

ance (R)

Objects

use different amount of po

werbecause

they have different amoun

ts of

current r

unning through them.

The

difference

in c

urrent is due to theresistance.Slide24

Resis

t

ance (R)

Resistance: the

tendency

for a materia

l to oppose

thefl

ow of

electrons

, c

hanging electrical

energy

into

thermal energ

y

and ligh

t

.

R

es

i

stance

mo

v

em

e

ntis caused by

internal friction, which slows theof charges through a conducting material. Resistanceis measured in Ohms (Ω).Slide25

Resis

t

ance and Wires…

Conducto

rs ha

ve low res

istance

 The

better the

conducto

r,

the bet

ter that

el

ectrons will

m

o

v

e

th

r

ou

g

h

the

ma

t

erial in thefield

 ie: metal wirespresenceofanelectric Insulators have high re

sistance The better the insulat

or, the more that

the substance w

ill resist the movement of electrons. ie:

plastic or

r

ubberSlide26

Resis

t

ance (R)

The res

istance of

a light bulb filament de

termines

how

bright the bulb will be

The

filame

nt of

a 40

watt bulb has a m

u

c

h high

e

r

resistance

than

a 100

w

att

bulb

This is because more resistance = less

current = dimmer bulb So being able to control resistance would be agood thing…a wire: 2 ways make make

that we can increase resistance inthe wire

longer

(ie: the

loops)wire thinner Thicker wire = less

resistance

 Thin wire

= more resistanceSlide27

Ohm’s

Law

V

= I x RV =

Voltag

e (units are v

olts,

v)I

= Current (

units are ampres

, A)

R = R

esistance

(units are ohm

s, Ω)Slide28

Practi

c

e!

The hea

d

lights

of a typical car a

re p

owered b

y a 12V

batter

y.

Wh

at

is the res

istance

of the headlights

if

th

e

y d

r

aw

3.0 A of

current

when

tu

r

ned

on?

Use

your Ohm’s Law Triangle---Insert your valuesUse unitsSolve!Slide29

SERIES

AND PARALLEL

CIRCUITSSlide30

Circuits

P

r

ovides

a path for electri

city to tr

avel

Similar to water pip

es in

your

Be

cause of the

v

oltage of

an wi

l

l

t

r

a

v

el

t

h

r

ough

the circuithouseoutlet,

electrons Electrons NEED to travelaround the ENTIRE pathfor anything to workSlide31

Open

v

s

.

Closed

Circuits

When the

re is

closed circuit

.

When the

re

is

a complete path,

the

c

ircuit is

c

onsi

d

e

r

ed

a

N

O

T

a complete

path,thecircuitisconsideredanopencircuit.

A switch allows you to

open

and c

lose a circuitSlide32

Conducti

v

e

Ink!!!

The

ink on this pa

ge cond

ucts electricity

ink).

(yes,

it

is sp

ecial

Whatov

e

r

?

happens

to the whenthepageisfoldedtoto tothethe thecirc

uit?lightbulb?current?Slide33

Safety

Precautions

If too

many dev

ices (t

v, radi

o, hair

connecte

d to

an outlet,

the ov

erall

cir

cuit is lo

w

er

e

d

This

inc

r

eases

the current

t

ravelingdrye

r, etc) areresistance of thethrough thecircuit, possibly more than a safe level This is called an over

loaded circuit.of

current.

 Too

much current traveling thougha wire can cause fires.Slide34

when

too

Safety

Precautions

Both

of these

ob

jects o

pen the circuit

by

dis

rupting the co

mplet

ecir

cl

e

,

pre

v

enti

n

g

d

a

m

a

g

e to the rest of the ci

rcuit. FUSE – a ribbon of metal wirethatmeltsmuch current flows through

 If current becomes too high,

the fuse me

lts,

and the circuit is open Can only be used oncethen

must

be replaced

itSlide35

Safety

Precautions

Circuit

Brea

ker opens a circu

itwith

a high curre

nt

Uses an e

lectro

magnet

that resp

onds

to current o

v

e

r

l

o

ad

b

y op

e

ning

the

cir

c

uit Basically it is magnetic s

witch that ‗trips‘ The circuit breaker acts as a switch. Can be used multiple times.reset once ―tripped.Must

beSlide36

Circuit

Diag

r

ams

Uses

symbols

to repre

sent par

ts of

a circuit

Shor

thand

way to describe

a real circuitSlide37

Circuit

Symb

o

ls:

H

o

w

to

D

r

aw

On

Off

Sw

i

tch

E

l

e

c

tr

i

cal

Sup

p

l

y

(Batt

e

ry)

R

e

s

i

st

o

r

L

i

g

ht

Bu

l

b

R

ememb

e

r

,

the

cir

c

uit

d

r

awing

ne

e

ds

to

b

e

a CO

M

P

L

ETE

path.Slide38

Circuit

Symb

o

ls:

H

o

w

to

Dr

awSlide39

Y

ou

try

to

d

raw

some

c

ircuit

s:A

circuit

sw

itch.

w

ith

one

r

esis

t

o

r

, one

b

a

t

t

e

r

y

,

andone

1.A circuitwithtworesistors, three batteries, and2.one swi

tch.Slide40

Circuits: 2 Diff Ty

p

es

Can

eit

her

be

series

or

p

arallel.

S

e

ries:

1 path

Pa

r

allel:

2+

P

athsSlide41

Resistance (

Ω

)

O

v

e

r

vi

e

w:

Series

v

P

a

r

a

l

lel

Ci

r

cui

t

s

M

U

ST

C

A

L

C

U

L

A

TE

(Volta

ge dr

ops to 0v afterSeriesParal

lel

P

at

hwa

ys

f

or

elect

r

ons

and cu

r

re

n

t

O

n

ly

1 pa

t

h.

M

u

l

t

ip

l

e

P

a

t

h

w

a

ys

f

or

c

u

rrent

C

u

r

r

ent

(I)

A

l

w

a

ys

t

h

e same

t

h

r

ou

g

ho

u

t

D

i

ffere

n

t

at

ea

c

h

b

r

a

n

c

h

V

olta

g

e (V)

V

O

L

T

A

GE

DROP after e

v

ery

resis

t

or/b

u

l

b

: M

U

ST

C

A

L

C

U

L

A

TE

ea

c

h

sepa

r

a

t

ely

Ea

c

h

B

r

an

c

h

sta

r

ts

wi

t

h

same

v

ol

t

a

g

e

ea

c

h

b

r

a

n

c

h)

A

d

d

up

all

to

g

et to

t

al

E

a

c

h

b

r

a

n

c

h

dif

f

erent

-

M

U

ST C

A

L

C

U

L

A

T

E

ea

c

h b

r

a

n

c

hSlide42

Let

s

Pr

actice:

Identify

WS…Slide43

Try

some

drawings!

1) Ser

ies: with 2 re

sistors

(one is 4 ohm,

12

V batter

y,

and

a 10 ohm

lig

ht b

ulb.

one is 7ohm), a

2)

P

a

r

allel:

wi

t

h a

1

.5

volt battery and 3

light bulbs(each on its own branch). Light bulbs have a resistanceof2, 4, and 6 ohms.

 3)Serie

s: 6v batter

y, o

ne switch, one 20ohm resistor.

4)

P

arall

e

l:

1

2

v

olt

b

a

tter

y

,

3 li

g

ht

bulb

s

.

2

li

g

ht

b

ulbs

(2

3

rd

and

3

ohms)

a

r

e

on

one

b

r

an

c

h,

while

the

(8

o

hms)

is

o

n

anoth

e

r

b

r

an

c

h)

light

bulbSlide44

Circuits: 2 Diff Ty

p

es

Can

eit

her

be

series

or

p

arallel.

S

e

ries:

1 path

Pa

r

allel:

2+

P

athsSlide45

Series

c

ircuits

There is o

nly 1 path for

current/electrons to t

ravel

 If

the circuit opens in a

ny w

ay, the

whol

e circuits

stops w

orking because current

S

T

OP

S

.Slide46

Series Circu

i

ts

Current only ta

kes one

path for elect

rons

If

you

remov

e a light bulb

or

one bu

rns

out—the

ENTIRE

circuit stops

w

o

r

king!

Current

stays

t

he sameas it flows thr

ough everypart ofthe circuit Resistance (and thereforevoltage), will change at different points on a series

circuitSlide47

Current

in Series

Curr

ent is the

same at a

ll

points

Elec

tric cur

rent

alw

ays FL

O

WS

f

r

om

po

s

iti

v

e

(+)

to

negative

(-) Which is OPPOSITE the flowof electrons. Use Ohm‘s Law to

find currentusing total resistance

andvoltag

eSlide48

Resis

t

ance

in

Seri

e

s

Add up all

resistors to get total

resistanceCurrent

MUST

go th

rough

each

resistor

in series beca

u

se

there

is only

one

path.Slide49

Vol

t

age

Serie

s

 Volt

age “

drops”after each r

esistor

has been passed.

Calculate

voltag

e drop

by

calculating v

olta

g

e

at ea

c

h res

i

stor

V

= I*R

V = (current * resistor)Slide50

Sample Problem #1

D

r

aw

a series

circuit with a 3 different1.5batteri

es (all

together),

2 equal resistors

, and a current

of 0.5 A.

V

What is

3

* 1.5What isV

= IR

What is

the

to

t

al

v

olta

g

e

of

the circuit?volts =

4.5 volts1.thetotal resistance of the circuit?2.4.5v / 0.5A=

9ohmstheresistance of

each

resistor?

3.9ohms / 2 equal resisto

rs

=

4.5

o

hms

e

a

c

hSlide51

Sample Problem #2

What

is the tot

a

l resist

ance of t

he circuit?

17ohms + 1

2ohms

+ 11ohms

= 40

o

hms

What

is

V

= IR

the

the

current

f

or the circu

i

t?

60

v

olts / 40ohms = 1.5ampsWhatisvoltage drop acrossV1 = IR

V1 = 1.5a * 17ohmV

1 = 25.5v

eac

h resistor?V3 = IRV3 = 1.5a *

12

ohm

V

3

= 18v

V

2

= IR

V

2

= 1.

5

a

*

1

1

o

h

m

V

2

= 1

6

.5vSlide52

Parall

e

l

Circuits

 Ha

ve more than

one path for curre

nt to flow

Paths are also kno

wn as

br

anches

If you remo

v

e a resisto

r

,

the

other b

r

an

c

hes

still

w

o

rkSlide53

Vol

t

age

in Paralle

l

 Voltag

e is the

sameacr

oss each b

ranch

because ea

ch bran

ch is

on the same wire

Volta

g

e

will

d

r

op

to

aft

e

r

ea

ch branch.0v

 But we won‘t calculatethat…Slide54

Current

in Parall

e

l

Current depends

on resistance in ea

ch branc

h

The curr

ent in e

ach

br

anch

will be

differ

ent

if

the r

e

si

s

to

r

s

ha

v

e di

fferent values It one

branch has less resistance, more charge will move through it because that bulb offers less opposition

to the movement of current.

 T

he su

m of the currents on each of theMUST equal the total starting cu

rren

t

br

anches

E

A

CH

B

R

ANCH

is

cal

c

ulated

using

Ohm

s

LawSlide55

Practice

problem

#3

Dr

aw a parallel

circuit

with two resistor

s,

one 2 ohm and on

e 3 ohm (o

ne on eac

hb

ranc

h) and a 12 V battery

.What

is the

12

v

o

l

ts

v

o

l

ta

g

e

through each

resistor?1.What isV = IRWhat isthecurrent flowing through each branch?

2.12v/2ohms =

6vtotal

current?

12v/3ohm = 4vthe3.

6v + 4v

= 10vSlide56

O

v

e

r

vi

e

w:

Series

v

P

a

r

a

l

lel

Ci

r

cui

t

s

M

U

ST

C

A

L

C

U

L

A

TE

(

V

ol

tage

drops to 0v aft

erSeriesParallel

P

a

thwa

ys for

elect

r

ons

and cu

r

re

n

t

O

n

ly

1 pa

t

h.

M

u

l

t

ip

l

e

P

a

t

h

w

a

ys

f

or

c

u

rrent

C

u

r

r

ent

(I)

A

l

w

a

ys

t

h

e same

t

h

r

ou

g

ho

u

t

D

i

ffere

n

t

at

ea

c

h

b

r

a

n

c

h

V

olta

g

e (V)

V

O

L

T

A

GE

DROP after e

v

ery

resis

t

or/b

u

l

b

: M

U

ST

C

A

L

C

U

L

A

TE

ea

c

h

sepa

r

a

t

ely

Ea

c

h

B

r

an

c

h

sta

r

ts

wi

t

h

same

v

ol

t

a

g

e

ea

c

h

b

r

a

n

c

h)

A

d

d

up

all

to

g

et to

t

al

E

a

c

h

b

r

a

n

c

h

dif

f

erent

-

M

U

ST C

A

L

C

U

L

A

T

E

ea

c

h b

r

a

n

c

hSlide57
Slide58

Magn

e

ts

A ma

gnet is an

object that

produ

ces a

a

mag

netic f

ield.

Magnets

can

be

n

at

u

r

al

or

man

made

 The only natu

ral metals that are naturally magnetized (and can become magnetized) are Nickel, Iron, Cobalt, and Ga

dolinium. If they are

made, they ar

e form

ed from things that are naturally magnetic .Slide59

Magn

e

tic

P

oles

 All

magnets

have 2

poles:

North and

South

La

ws of

att

raction still a

p

pl

i

es

Li

k

e

po

l

es

r

epel, opposite poles att

ract If a magnet is cut, each piece will still have two polesSlide60

P

er

m

ane

n

t Magn

ets

Substanc

es that a

re m

agnetic all

the

time

 Can

chang

e an

ything into

a

ma

g

net

b

y

rub

b

i

n

g

a permanent magnet over it sever

al times Permanent magnets can have magnetic properties but not always be a magnet (ex: iron)

Permanent magnets can last f

or minut

es, or

foreverSlide61

Magn

e

tic

Fields

When

magnets repel or

attr

act each other it

’s because

of their mag

netic

fields

Magneti

c field – r

egion

w

h

e

r

e

a magnetic

f

o

r

c

e

can be detectedSlide62

Magn

e

tic

Fields

Bel

o

w: Iron

filings pl

aced o

ver a

magnet align

with the

magnetic

field

of the magn

etSlide63

Magn

e

tism

and Ele

c

tric Curre

nts

Ele

ctric c

urren

ts p

roduc

e m

agnetic f

ields

 Magnetism is

p

r

odu

c

ed

b

y

m

o

ving

electric

charges The magnetic f

ield of a coil of wire resemblesthat of a bar magnetSlide64

Elect

r

omagn

e

ts

A

strong m

agnet crea

ted w

hen an i

ron

c

or

e is

in

serted int

o

the

c

en

t

er

c

u

r

r

e

nt-

c

arrying coil of wir

eStrength depends on: Thicker wire Thicker wire = less resistance the number

of loops in the wire

More loops

= stron

ger the amount of current More

cur

rent

= str

onger

of

a

And

r

emembe

r

,

mo

r

e

v

olt

a

g

e

means

mo

r

e

cur

r

ent

si

z

e

of

the

i

r

on

c

o

r

e

B

i

g

g

er

c

o

r

e

=

st

r

on

g

erSlide65

Elect

r

omagn

e

ts

So

why a

re elect

romagnetsuseful?

Can tu

rn

them on

/ off

C

u

t

t

i

ng

the

c

u

r

rent off turns off the magnet

 Can control their strength Just like we talked about last slide.

 More current and

voltage

Bigger Iron core More

c

oi

ls a

ro

u

nd

the

i

r

on

c

o

r

eSlide66

Mo

t

o

r

s

Electri

c moto

rs chang

e electri

cal ene

rgy

to

mechani

cal en

erg

y

Do

n

e

b

y

running

an

elect

r

ic currentmake an electr

omagnet.throughcoilsto When the electric current runsthrough the armatu

re, it becomesmagnetized

 The armat

ure spins

because motors use other magnets to push and pull the armature

and cr

eate motion.Slide67

Gen

e

r

at

o

rs

 Chan

ge mecha

nical ene

rgy in

to electric

energ

y

 Done

by

mo

ving a coil

pa

s

t

a

magnetic

f

ield.

U

se

electromagnetic in

duction to produce an electriccurrent. When a coil of wire moves through a magnetic field

an electric current can be pro

duced. This is

elect

romagnetic induction. Produces

AC

current.