Ohm's Law Calculator
Calculate voltage, current, and resistance using Ohm's law for electrical circuits
Voltage (V)
Current (I)
Resistance (R)
Power (P)
Formula Used
Understanding Ohm's Law
Ohm's Law is a fundamental principle in electrical engineering and physics that describes the relationship between voltage, current, and resistance in an electrical circuit. Formulated by German physicist Georg Simon Ohm in 1827, it states that the current through a conductor between two points is directly proportional to the voltage across the two points, and inversely proportional to the resistance between them.
Core Formulas
- V = I × R — Voltage equals current times resistance
- I = V / R — Current equals voltage divided by resistance
- R = V / I — Resistance equals voltage divided by current
Power Formulas
- P = V × I — Power equals voltage times current
- P = I² × R — Power equals current squared times resistance
- P = V² / R — Power equals voltage squared divided by resistance
Variables Explained
Voltage (V)
- • Measured in Volts (V)
- • The electrical potential difference between two points
- • Think of it as the "pressure" pushing electrons through a circuit
- • Named after Alessandro Volta
Current (I)
- • Measured in Amperes (A)
- • The rate of flow of electric charge
- • Think of it as the "flow rate" of electrons
- • Named after André-Marie Ampère
Resistance (R)
- • Measured in Ohms (Ω)
- • The opposition to the flow of electric current
- • Think of it as the "friction" that impedes electron flow
- • Named after Georg Simon Ohm
Power (P)
- • Measured in Watts (W)
- • The rate at which electrical energy is converted
- • Think of it as the "work done" by the circuit per second
- • Named after James Watt
Practical Examples
LED Circuit
A typical LED operates at about 2V and 20mA. Using Ohm's Law with a 5V power supply: R = (5V - 2V) / 0.02A = 150Ω. You would need a 150Ω resistor in series with the LED.
Household Light Bulb
A 60W light bulb on a 120V circuit draws: I = P / V = 60W / 120V = 0.5A of current. Its resistance is: R = V / I = 120V / 0.5A = 240Ω.
USB Charging
A USB port supplies 5V. If a phone charger draws 2A, the power delivered is: P = V × I = 5V × 2A = 10W. The effective load resistance is: R = V / I = 5V / 2A = 2.5Ω.
References
The formulas and principles used in this calculator are based on well-established physics and electrical engineering sources:
Related Calculators
Note: This calculator assumes ideal conditions with purely resistive (ohmic) components. Real-world circuits may include reactive components (inductors, capacitors) where Ohm's Law in its basic form does not apply directly. Results are for educational and estimation purposes.
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