Electricity & Magnetism

Electric charge is a fundamental property of matter measured in coulombs (C). One coulomb equals about 6.24 x 10^18 elementary charges; the elementary charge e is approximately 1.602 x 10^-19 C.

Current is the rate of flow of charge: I = dQ/dt, measured in amperes (A), where one ampere equals one coulomb per second.

I = Q/t = 12 C / 4 s = 3 A.

Voltage is the energy per unit charge between two points: V = W/Q, measured in volts (V), where one volt equals one joule per coulomb.

Ohm's law: V = IR, where V is voltage in volts, I is current in amperes, and R is resistance in ohms. It applies to ohmic (linear) resistors.

R = V/I = 24 V / 6 A = 4 ohms.