Download Resitance and Resistivity - 2010-ComprehensivePortfolio

Bellwork
If it takes 8 Joules of work to
move a charge of 2 coulombs
around a circuit, then what is the
potential difference in the
circuit?
Bellwork
If you made a cylinder of Play-Doh and measured the
diameter of the cylinder to be 2 cm, then what will the
cross-sectional area of the Play-Doh cylinder be?
2 cm
Play-Doh Lab
A = πr² = π(d/2)² = (πd²)/4
KNEAD THE DOUGH
Connect the multimeters correctly
Measure simultaneously
d
MATERIALS:
L
3 wires
2 multimeters
2 nails
1 battery
1 Play-Doh color
1 Ruler
1 calculator
RESISTANCE/RESISTIVITY
Resitance and Resistivity
Resistance is the opposition a device offers to the flow of electric current.
Resistivity is a characteristic of a material that depends on its electronic
structure and temperature. (Type of metal)
A resistor is a device designed to have a definite amount of resistance.
Resistivity of Play-Doh Colors
Resistivity
R
L
A
R = Resistance (Ohms – Ω)
ρ = Resistivity (Ω·m)
L = Length (m)
A = Area (m²)
Graphing
Resistance vs. Length
R (Ω)
Resistance vs. Cross-Sectional Area
R (Ω)
L (m)
A = (m²)
Resistance is strongest when the wire is the longest and thinnest
Example 1
Calculate the resistance of a 4.00-meter length of
copper wire having a diameter of 2.00 millimeters.
ρcopper=1.72 x 10-8 Ωm
Example 2
Say a wire has resistance of 5.76 x 10-3 ohm. If its
length is 4 meters long and its cross-sectional area is
1.96 x 10-5 meters squared then what is the wires
resistivity? Using the table, which metal does this
correspond to?
Example 3
A wire has a resistivity of 5.6 x 10-8 ohm meters, a length
of 0.01 meters, and a cross-sectional area of 3.14 x 10-10
meters squared. What is the resistance of this wire?
Example 4
Which of the following will provide the most resistance in a wire?
(a)
(b)
(c)
(d)
Doubling the area and doubling the length of the wire
Doubling the area of the wire
Doubling the length of the wire
Not doing anything to the wire
Bellwork
What is one thing I can change about a wire to
increase the resistance it has in a circuit?
Ohm’s Law
V  IR
V = voltage (V)
I = current (A)
R = resistance (Ω)
Graphing
Slope = Resistance (Ω)
V
R
I
Voltage (V)
Current (A)
Example 1
If you measure that a circuit has a current of 0.20
amperes and there is a potential difference of 15 volts
across a light bulb, then what is the resistance through
that light bulb?
Example 2
A simple circuit has a total resistance of 1.2 x 10² ohms and
an applied potential difference of 2.00 x 10² volts. What is
the current at any particular point in the circuit?
Example 3
An electronic device has a resistance of 3 ohms and a
current of 4 amperes. What is the voltage drop across
the device?
For Test:
R
Charge of an electron = 1.6 x 10-19 Coulombs (C)
L
A
R = Resistance (Ohms – Ω)
ρ = Resistivity (Ω·m)
L = Length (m)
A = Area (m²)