Physics Unit 2 Study Guide: Circuit Characteristics, Non-Ohmic Components, Thermistors, and Internal Resistance

Ohmic Conductors

• Ohm's Law: Current ($I$) is directly proportional to voltage ($V$) when physical conditions (such as temperature) remain constant.

• $I-V$ Graph: Linear straight line passing through the origin $(0,0)$.

• Slope: Slope equals $rac{I}{V} = rac{1}{R}$ (resistance $R$ is constant).

• Symmetry: Identical linear behavior in both forward and reverse bias.

Filament Bulb

• Behavior: Non-ohmic device; resistance $R$ increases as current increases.

• Physical Mechanism:

  • Current generates heat, raising the filament's temperature.

  • Higher temperature increases thermal vibrations of metal lattice ions.

  • Increased electron-ion collisions impede charge flow, causing an increase in electrical resistance ($R$).

• $I-V$ Graph: Non-linear S-shaped curve that levels off at higher positive and negative voltages.

Semiconductor Diode

• Behavior: Non-ohmic device; conducts current primarily in one direction.

• Forward Bias: Current is negligible until threshold voltage is reached, after which resistance drops rapidly and current increases exponentially.

• Reverse Bias: Extremely high resistance; virtually zero current flows.

• Physical Mechanism: Controlled by the p-n junction depletion region, which narrows in forward bias and expands in reverse bias.