What is Ohm's Law?
Ohm's Law is a fundamental principle of electrical engineering discovered by German physicist Georg Ohm in 1827. It states that the electric current ($I$) flowing through a conductor between two points is directly proportional to the voltage ($V$) across the two points, and inversely proportional to the resistance ($R$).
The 3 Fundamental Ohm's Law Equations
- Voltage (Volts): V = I × R
- Current (Amperes): I = V / R
- Resistance (Ohms): R = V / I
Electrical Power & Joule's Law
Electrical power ($P$), measured in Watts (W), represents the rate at which electrical energy is transferred or dissipated as heat in a circuit. Combining Ohm's Law with Joule's Law gives the 12 classic relationship equations:
| Quantity | Formula Using V & I | Formula Using V & R | Formula Using I & R |
|---|---|---|---|
| Power (P) | P = V × I | P = V² / R | P = I² × R |
| Voltage (V) | V = P / I | V = √(P × R) | V = I × R |
| Current (I) | I = P / V | I = V / R | I = √(P / R) |
| Resistance (R) | R = V / I | R = V² / P | R = P / I² |
Frequently Asked Questions
What happens to current if voltage increases?
If resistance remains constant, increasing voltage causes current to increase proportionally (I = V / R).
How do I size a resistor for an LED?
Subtract the LED forward voltage ($V_f$) from your supply voltage ($V_s$), then divide by desired forward current ($I_f$): R = (V_s - V_f) / I_f. For a 5V supply and 2V LED at 20mA: (5 - 2) / 0.02 = 150 Ω.
How do I convert Watts to Horsepower?
One mechanical horsepower is equal to approximately 745.7 Watts (0.7457 kW).
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