Electricity — Key ideas
Electric current is the rate of flow of charge: I = Q/t (ampere).
Potential difference V = W/Q (volt). Ohm's law: V = IR.
Resistance depends on material, length and area: R = ρℓ/A.
- Series: R = R₁ + R₂ + …
- Parallel: 1/R = 1/R₁ + 1/R₂ + …
Electric power P = VI = I²R = V²/R.
Practice: numerical problems on combination of resistors and household circuits.