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
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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
sferredObje
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 waterElectrical Insulator: a material in whichcharg
es cannot move freely
i.e. plastic,
wood,
glass, foam, cloth, ceramicSlide11
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
resistanceCurrent
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 = 1.5ampsWhatisvoltage 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
hSlide57Slide58
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.