Lesson 10.4: Current, Resistance, & Ohm’s Law - Summary

Key Concepts: Current, Resistance, & Ohm’s Law

Electric Current

  • Current is the rate of flow of charge: I = Q/t. Unit: Ampere (A). 1 A = 1 C/s.
  • Conventional current flows from + to − (opposite to electron flow).

Resistance

  • Resistance opposes current flow: R = ρL/A, where ρ = resistivity, L = length, A = cross-sectional area.
  • Unit: Ohm (Ω). Resistivity depends on material and temperature.

Ohm's Law

V = IR

  • The voltage across a resistor equals current times resistance.
  • Ohm's law applies to ohmic materials — those with constant resistance (e.g., metals at constant temperature).
  • Non-ohmic: diodes, filament bulbs (resistance changes with current/temperature).

Power: P = IV = I²R = V²/R.

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