1. Electrical Stopping Power 4.2.2 Electrical Resistance

2. Definitions resistance: OPPOSITION TO CURRENT unit: Ω
factors that change resistance:
resistivity: MATERIAL
length
cross-sectional area
temperature

3. Resistance Factors R ρ R A
NEXT R L R
Temp.

4. LOW RESISTIVITY, SHORT, WIDE, COLD
Resistance Factors R ρ R A
To build an “ideal” conductor with the smallest possible resistance you would select one that is:
LOW RESISTIVITY, SHORT, WIDE, COLD R L R
Temp.

5. Example #1
Determine the resistance of a 1.0 meter long copper wire with a cross-sectional area of 0.01 meter2.
R = ρL / A
R = (1.72 x 10-8 Ω·m)(1.0 m) / (0.01 m2)
R = 1.72 x 10-6 Ω

6. Example #2
A piece of wire that has a length of 5.0 x 107 meters and a cross-sectional area of meter2 has a resistance of 31.8 ohms.
What is the composition of this wire?
R = ρL / A
ρ = RA / L
ρ = (31.8 Ω)(0.025 m2) / (5.0 x 107 m)
ρ = 1.59 x 10-8 Ω·m

7. End of PRACTICE