Current (I), measured in Amperes (A), is the rate of flow of charge (Q), measured in Coulombs (C), per unit time (t):
I = Q/t
Voltage (V), measured in Volts (V), is the energy (E), measured in Joules (J), transferred per unit charge (Q):
V = E/Q
Resistance (R), measured in Ohms (Ω), opposes the flow of current.
Ohm's Law:
V = IR
For ohmic conductors, the V-I graph is a straight line through the origin.
Series circuits: same current throughout, voltage is shared across components.
R_total = R1 + R2
Parallel circuits: same voltage across each branch, current splits.
1/R_total = 1/R1 + 1/R2