Using Ohm's Law, if a circuit has 12 volts and 4 ohms of resistance, what is the current?

Ohm's Law: V = IR (Voltage = Current × Resistance). Rearranged: I = V/R, or R = V/I. With V = 12, R = 4: I = 12/4 = 3 A. Master these three forms: (1) V = IR (find voltage given current and resistance); (2) I = V/R (find current given voltage and resistance); (3) R = V/I (find resistance given voltage and current). Power equations (often combined with Ohm's Law): P = VI; P = I²R (since V = IR); P = V²/R (since I = V/R). Choose based on what's known. Example: 12V circuit, 4Ω resistance. Current = 3 A (just calculated). Power = VI = 12 × 3 = 36 W; or I²R = 9 × 4 = 36 W; or V²/R = 144/4 = 36 W — all give the same answer. Common ASVAB EI calculations: (1) Find current in a circuit; (2) Find voltage across a resistor; (3) Find resistance needed for desired current; (4) Find power consumption; (5) Total resistance in series/parallel circuits. SERIES circuit: R_total = R₁ + R₂ + R₃ + ... (resistances add); same current through all; voltages add up to source. PARALLEL circuit: 1/R_total = 1/R₁ + 1/R₂ + 1/R₃ + ... (reciprocals add); same voltage across all branches; currents add up to source current. For two parallel resistors: R_total = (R₁ × R₂) / (R₁ + R₂). Parallel resistance is always LESS than the smallest individual resistance.