Electrical Stopping Power 4.2.2 Electrical Resistance

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

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

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.

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

Example #2 A piece of wire that has a length of 5.0 x 107 meters and a cross-sectional area of 0.025 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

End of 4.2.2 - PRACTICE