1. Resistance R - _____________________________________
____________________________________________________
_____________________________________________________
the opposition that a device or
conductor offers to the flow of electric current.
More resistance  less current, and vice versa.
1. Resistance occurs as a result of ________________
colliding with ___________________ and with the
__________________________ , resulting in ____________ .
This converts __________________energy to ___________.
electrons
other electrons
material of the conductor
friction
electrical
heat
2. R is a __________________ . It has _________________ .
units of R: ___________________
It is a ______________________ unit.
scalar
no direction
ohms, W
derived
3. Any factor that makes it more _________________for
_______________ to move will through a material will
__________________________________ of the material:
difficult
electrons
increase the resistance

4. A metals For _____________, there are four factors that affect
how much resistance it has:
metals
length L:
A. __________________ R
more R L
cross-sectional area A:
B. __________________ R A A
less R A

6. Higher T  atoms of the metal _________________
temperature:
C. __________________ R T
more R
Higher T  atoms of the metal _________________
 ________________________ for e-'s
to move through the metal
 more ____________________
vibrate faster
more difficult
resistance
D. ______________________ : Different metals have different numbers of ____________________ .
 ______ electrons
 ______ current
 _______ resistance
The material
free electrons
more R
more
less
# of free electrons

8. These 4 factors are summed up in:
rL/A
(rho) is called the _________________ of a material.
depends on the ___________________ of a metal
and is different for different _____________ .
resistivity
temperature
metals
units of r:
_________________
ohm·meter, W·m
(derived)
Lowest r = _______________
Highest r = _______________
Metals that have more free
_____________ will have a
_________ r and _________ R.
silver
nichrome
electrons
lower
lower

11. Ex. Calculate the resistance of 100 meters of copper
wire that has a cross-sectional area of 3.44 x 10-6 m2.
R = rL A
(1.72 x W·m)
(100. m) =
(3.44 x m2) = W

12. A _________________is a device that is designed to
have a definite amount of _________________.
resistor
resistance
Resistors are used to
1. control _____________ flow; and
2. provide a _____________________
of a certain amount.
current
potential difference
Symbols:
1. resistor:
2. variable resistor:

13. Resistors
Bigger resistors can handle more power w/o overheating.

15. Variable resistors:
Just
turn
the
knob!
(It's
that
easy.)
As you turn the knob, this "arm"
swivels around and connects more
and more wire into the circuit.
More wire more R

16. Two materials that do not follow these rules for metals
are _____________________ and ______________________ .
semiconductors
superconductors
Semiconductors (like ___________ and ______________ )
have ____________ resistance at higher temperatures.
Here’s why:
silicon
germanium
less
___________ silicon (Si) is
an _______________________ .
It _____________ its outer e-’s
with 4 other silicon atoms in
a ___________________ bond,
so that its own electrons
_______________________
electricity.
Pure
= Si atom
insulator
shares
covalent
cannot conduct
bond
= a ________ of
shared e-s

17. 3 4 5 B C N Al Si P Ga Ge As Phosphorus P and arsenic As
outer
e-’s 3 4 5 B C N Al Si P Ga Ge As
Phosphorus P and arsenic As
have __________ outer e- than Si.
Boron B and gallium Ga
If you add _________________ of P, As, B or Ga to pure Si, it creates extra charge carriers. This is called _____________ . Higher temps “free up” more of these extra charges and allows for more __________ and so less _____ . And because of the extra charge carriers,
semiconductors have _________________ resistances
that can be ______________ . They are now used in making almost all _______________________________ .
1 more
1 less
tiny amounts
doping
current R
average
controlled
tiny electrical devices

19. Superconductors:
The resistance R of superconductors is _________
as long as the material is _____________________________.
Because they have no _____ , electrons can travel through
them __________ , and so they can carry ________ currents
for _________________ without producing large amounts
of ___________ . This is useful in the ___________________
___________ and _________________________________________
Originally (around 1911), only certain ____________
were found to be superconducting. But they had to be
cooled to near ___________________ using liquid helium
(boiling point about _______ ) for this to happen.
This is very expensive.
below a "critical" temperature R
freely
large
long times
transmission
heat
creating strong magnets (medical use).
of power
metals
absolute zero
4 K

20. The current just keeps going….

23. In _______, a new type of superconductor was discovered whose makeup is similar to ________________ . These become superconductors at higher temperatures. This makes them much more ____________________.
1986
ceramics
Material
metal=m
ceramic=c
critical temp.
(K)
absolute zero
Zinc m
0.88
Aluminum
1.19
Tin
3.72
Mercury
4.15
liquid nitrogen
YBa2Cu3O7 c 90
TlBaCaCuO
125
room temp.
293
much ___________
to use liquid N

24. Who uses ceramics?
Harry Potter!

25. In _______, a new type of superconductor was discovered whose makeup is similar to ________________ . These become superconductors at higher temperatures. This makes them much more ____________________.
1986
ceramics
affordable
Material
metal=m
ceramic=c
critical temp.
(K)
absolute zero
Zinc m
0.88
Aluminum
1.19
Tin
3.72
Mercury
4.15
liquid nitrogen
YBa2Cu3O7 c 90
TlBaCaCuO
125
room temp.
293
cheaper
much ___________
to use liquid N 77

26. Applications of Superconductivity:
Medicine
Strong currents easy to maintain
 strong magnetic fields are used in:
MRI (magnetic resonance imaging)
NMR (nuclear magnetic resonance)

27. Transportation:
 strong currents run forever
 strong currents produce strong magnetic fields
 use repulsion or attraction to levitate train
 no friction
maglev trains

28. Power Transmission:
no resistance  no heat loss  more efficient

29. The Meissner Effect - A superconductor expels a magnetic field.
A magnet is levitating above a superconductor (cooled by liquid nitrogen)