2. Negatively charged particles
Electron Orbitals
Orbits in which electrons move
around the nucleus of an atom
Valence Electrons
The outermost ring of electrons
in an atom
3D
2D
Electrons
4. Atoms like to have their valence ring either filled (8) or empty(0) of
electrons.
How many electrons are in
the valence orbit?
Copper
Cu
29
1
Is copper a conductor or
insulator? Conductor
Why?
Electron Orbits
5. Electricity is created as electrons collide and transfer from atom to atom.
Electron Flow
Play Animation
6. Conductors Insulators
Electrons flow easily
between atoms
1-3 valence electrons in
outer orbit
Examples: Silver,
Copper, Gold, Aluminum
Electron flow is difficult
between atoms
5-8 valence electrons in
outer orbit
Examples: Mica, Glass,
Quartz
11. Resistance
Resistance: is a measurement of how strongly
an object will oppose current
An object’s resistance depends on FOUR factors:
Resistivity Length
Cross-sectional Area Temperature
Is specific to a material – the
higher it is, the more natural
resistance the material has.
How big is the object across?
The wider it is, the more
current it will allow to pass.
How long is the object?
The longer it is, the more it will
oppose current flow.
If the object is warm, the
molecules inside will be
bouncing around more –
opposing current.
13. We would like to have conductors that allow
CURRENT to flow from one place to
another EASILY
“IDEAL” conductor minimum RESISTANCE
LONG or SHORT?
WIDE or NARROW?
HOT or COLD?
SHORTER conductors have lower resistance because:
electrons do not have to travel as far!
WIDER conductors have lower resistance because:
electrons have more room to pass!
COLDER conductors have lower resistance because:
atoms are not as energetic – don’t interfere with electrons
The “IDEAL” conductor has a
LOW RESISTIVITY and is
SHORT, WIDE, and COLD
14. Factors that affect resistance
Length: Length
Area: Area
Temperature: Temp
Resistance
Resistance
Resistance
R =
rL
A
15. Example #1
◎ Calculate the electrical resistance
provided by a piece of copper wire with a
length of 1 meter and a cross sectional
area of 0.01 m2.
A
R
)
01
.
0
(
)
1
)(
10
72
.
1
(
2
8
m
m
m
R
6
10
72
.
1
R
Material Resistivity
Aluminum 2.82 x 10-8
Copper 1.72 x 10-8
Gold 2.44 x 10-8
Nichrome 150 x 10-8
Silver 1.59 x 10-8
Tungsten 5.60 x 10-8
16. ◎ Determine the composition of a wire with a
resistance of 31.8 Ohms if it is 5 x 107
meters long and has a cross-sectional area
of 0.025 m2.
A
R
)
025
.
0
(
)
10
5
(
8
.
31 2
7
m
m
m
8
10
59
.
1
SILVER
Example #2
25. Which of the following sentences
describes what will happen to a wire
in a circuit if a very large current is
passed through it?
A. The wire will cool down.
B. The wire will heat up.
C. The wire will neither heat up nor cool down.
26. Which of the following is the correct
unit for electrical resistance?
A. The joule
B. The volt
C. The ohm
D. The watt
E. The ampere
27. Any wire will have some amount of
resistance. There are two unequal
lengths of identical wire. Which one
of the following sentences is
correct?
A. The wire of greater length has the greater
resistance.
B. The wire of greater length has the lower
resistance.
C. Both wires will have the same resistance.
28. Which of the following is the correct
unit symbol for ohms?
A. O
B. R
C. o
D. 𝜔
E. Ω
29. If a component in a circuit has a
higher electrical resistance, is it
easier or harder for charges to move
through it?
A. Easier
B. Harder
