Physics & Technology
Ohm's Law Calculator: Understanding Electrical Circuits
Learn Ohm's Law (V=IR), how to calculate voltage, current, and resistance, and apply it to real circuits.
Ohm's Law is the foundation of electrical engineering. It describes the relationship between voltage, current, and resistance in a circuit.
Ohm's Law Formula
V = I × R, where V is voltage (volts), I is current (amps), and R is resistance (ohms). You can rearrange to solve for any variable: I = V/R or R = V/I.
The Ohm's Law Triangle
Visual memory aid: V on top, I and R on bottom. Cover the variable you want: V over I×R gives V=IR; V over I gives R=V/I; V over R gives I=V/R.
Power Relationship
Power (watts) = Voltage × Current (P = VI). Combined with Ohm's Law: P = I²R or P = V²/R.
Practical Examples
- LED circuit: 9V battery, LED needs 2V at 20mA. Resistor needed: (9-2)/0.02 = 350 ohms
- Household: 120V outlet, 15A breaker. Maximum load: 120 × 15 = 1800 watts
- Car battery: 12V system, 100W headlight. Current draw: 100/12 = 8.33 amps
Series vs Parallel Circuits
Series: resistances add (R_total = R1 + R2 + ...). Parallel: reciprocals add (1/R_total = 1/R1 + 1/R2 + ...).
Frequently Asked Questions
What is Ohm's Law?
Ohm's Law states that current through a conductor is directly proportional to voltage and inversely proportional to resistance: V = IR.
How do I calculate resistance?
R = V / I. Divide voltage (volts) by current (amps). Example: 12V / 2A = 6 ohms.
What happens if resistance is too low?
Too low resistance causes excessive current, which can overheat wires, trip breakers, or cause fires. This is called a short circuit.