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

d

Play-Doh Lab

L

A = πr² = π(d/2)² = (πd²)/4

MATERIALS:

3 wires

2 multimeters

2 nails

1 battery

1 Play-Doh color

1 Ruler

1 calculator

KNEAD THE DOUGHConnect the multimeters correctlyMeasure simultaneously

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

A

LR

R = Resistance (Ohms – Ω)ρ = Resistivity (Ω·m)L = Length (m)A = Area (m²)

GraphingResistance vs. Length Resistance vs. Cross-Sectional Area

R (Ω) 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 2Say 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) Doubling the area and doubling the length of the wire(b) Doubling the area of the wire(c) Doubling the length of the wire(d) 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

IRV V = voltage (V)I = current (A)R = resistance (Ω)

Graphing

Voltage (V)

Current (A)

Slope = Resistance (Ω)

I

VR

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:

A

LR

R = Resistance (Ohms – Ω)ρ = Resistivity (Ω·m)L = Length (m)A = Area (m²)

Charge of an electron = 1.6 x 10-19 Coulombs (C)