Ohm’s Law (V = IR)
Georg Ohm discovered in 1827 that current through a conductor is directly proportional to voltage and inversely proportional to resistance, for materials that obey Ohm's law (ohmic materials). This is the single most important equation in electronics — it relates the three fundamental quantities.
Electrical Power (Joule's Law)
Power is the rate of energy conversion. When current flows through a resistor, electrical energy becomes heat (Joule heating). This is why resistors get hot and why power supplies have efficiency ratings. The heat dissipated is P = I²R = V²/R. A component's power rating tells you its maximum safe dissipation before damage.
Energy & Efficiency
Energy (Joules) = Power × Time. 1 kWh = 3.6 MJ, the unit on your electricity bill. Circuit efficiency η = P_out / P_in × 100%. Linear regulators (like 7805) dissipate excess as heat (η can be <50%). Switching regulators achieve 85-95% efficiency. For battery-powered devices, efficiency directly determines battery life.
🎮 Ohm's Law Calculator
🎮 Ohm's Law Calculator
Drag sliders for V and R — instantly see current and power with visual feedback.
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Power (P = V \u00D7 I)
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Q: 12V battery, 240Ω resistor. What current flows?
A: I = V/R = 12/240 = 0.05A = 50mA
Q: Same circuit. What power does the resistor dissipate?
A: P = VI = 12×0.05 = 0.6W — use at least a 1W resistor.
Q: A 5V USB charger delivers 2A. What's the equivalent load resistance?
A: R = V/I = 5/2 = 2.5Ω
Q: 100Ω, 1/4W resistor. Max safe voltage?
A: V = √(P×R) = √(0.25×100) = 5V