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Ohm's lawOhm's Law defines the relationship between voltage, current and resistance in an electrical circuit. The law was named after the German physicist Georg Simon Ohm. Ohm's Law states that the current passing through a conductor between two points is directly proportional to the voltage across them, and inversely proportional to the resistance. When you introduce Joule's Law of heating (Power), these relationships expand into a comprehensive matrix of 12 distinct formulas. Quick Reference Calculation Matrix
Use our online Ohm's Law Calculator. Frequently Asked QuestionsWhy does current drop when resistance increases if voltage stays constant? Resistance is literally the friction or physical opposition to the flow of electrical charges. Think of voltage as water pressure in a pipe and current as the water flow rate. If you constrict the pipe (increase resistance) while keeping the pump pressure (voltage) exactly the same, less water can push through per second. Therefore, as resistance climbs, the current drops proportionally, which perfectly mirrors the inverse relationship defined by I = V / R.
Does Ohm's Law apply to AC (Alternating Current) circuits? Yes, but with an important caveat. For purely resistive AC loads, such as incandescent light bulbs, electric blankets, or water heaters, Ohm's Law applies exactly the same way as it does in DC circuits. However, if the AC circuit contains reactive components like capacitors or inductors, standard DC resistance (R) must be replaced with Impedance (Z), changing the formula to V = I × Z. Impedance accounts for frequency-dependent phase shifts that DC calculations ignore.
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