Electrical Stopping Power Introduction to Resistance

Resistance Resistance: is a measurement of how strongly an object will oppose current An object’s resistance depends on several factors: Resistivity Length Some materials are better conductors than others. Longer objects are more difficult to pass current through. Cross-sectional Area Temperature Wider objects allow current to pass more easily. If the object is warm, the molecules inside will be bouncing around more – opposing current.

Equation Unit for Resistance is the: OHM Ω R = resistance

Resistance in Wires The “IDEAL” conductor has a LOW RESISTIVITY and is We would like to have wires (conductors) that allow CURRENT to flow from one place to another EASILY “IDEAL” conductor  minimum RESISTANCE The “IDEAL” conductor has a LOW RESISTIVITY and is SHORT, WIDE, and COLD WIDE or NARROW? LONG or SHORT? HOT or COLD? COLDER conductors have lower resistance because: atoms are not as energetic – don’t interfere with electrons WIDER conductors have lower resistance because: electrons have more room to pass! SHORTER conductors have lower resistance because: electrons do not have to travel as far!

Plug in the factor each changes by Example #1 If the length of the wire is doubled, what happens to the resistance of the wire? Plug in the factor each changes by Doubles!!!

Plug in the factor each changes by Example #2 What happens to the resistance of a wire if the resistivity is cut in half, and the cross sectional area is increased by a factor of 8? Plug in the factor each changes by ¼ As Large

Plug in the factor each changes by Example #3 If the length doubles, the resistivity is decreased to ¼ its original value, and the cross sectional area is tripled, what happens to the resistance of the wire? Plug in the factor each changes by 1/6 As Large

If the length of the wire is… what happens to the resistance? Doubled Quadrupled If the resistivity of the wire is changed by a factor of… what happens to the resistance? 3times greater ½ as large If the surface area of the wire is… what happens to the resistance? 10times larger ¼ as large