AP Physics C: Electricity and Magnetism / Unit 11: Electric Circuits
11.3 Resistance, Resistivity, and Ohm's Law
Notes
$$R=\frac{\rho L}{A},\qquad \Delta V=IR,\qquad \vec J=\sigma\vec E$$
- For nonuniform wires: $\displaystyle R=\int\frac{\rho\,dl}{A}$.
- Resistivity usually increases with temperature in metals.
Practice
Stretching a wire to twice its length (same volume) makes $R$:
$L$ doubles, $A$ halves.
Resistivity depends on:
A material property.
Ohm's law is $V=IR$ for:
Diodes aren't ohmic.
Ready for more? Take the Unit 11 test.