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Enter Known Values
Quick Scenarios
Calculated Values
Voltage (V)
12.0000 V
Current (I)
3.0000 A
Resistance (R)
4.0000 Ω
Power (P)
36.0000 W
Ohm's Law Formulas
Voltage (V)
V = I × R
V = P / I
V = √(P × R)
Current (I)
I = V / R
I = P / V
I = √(P / R)
Resistance (R)
R = V / I
R = V² / P
R = P / I²
Power (P)
P = V × I
P = V² / R
P = I² × R
Your Calculation
Given:
Voltage = 12 V, Resistance = 4 Ω
Current:
I = V / R = 12 / 4 = 3.0000 A
Power:
P = V × I = 12.0000 × 3.0000 = 36.0000 W
Common Reference Values
| Component/Device | Typical Voltage | Typical Current |
|---|---|---|
| AA Battery | 1.5 V | - |
| USB Port | 5 V | 0.5-3 A |
| Car Battery | 12 V | Varies |
| US Wall Outlet | 120 V | 15-20 A max |
| EU Wall Outlet | 230 V | 13-16 A max |
| LED (typical) | 2-3 V | 20 mA |
Quick Answer
Ohm's Law states V = I x R (Voltage = Current x Resistance). To use: enter any two known values to calculate the other two. Key formulas: V = IR, I = V/R, R = V/I, P = VI, P = I^2R, P = V^2/R. For example, with 12V and 4 ohms resistance: Current = 12/4 = 3 Amps, Power = 12 x 3 = 36 Watts. Units: Voltage (Volts), Current (Amps), Resistance (Ohms), Power (Watts).
Key Facts
- Ohm's Law: V = I x R (Voltage = Current x Resistance)
- Power formulas: P = VI, P = I^2R, P = V^2/R
- Units: Voltage (V), Current (A), Resistance (Ohms), Power (W)
- Resistance in series: R_total = R1 + R2 + R3...
- Resistance in parallel: 1/R_total = 1/R1 + 1/R2 + 1/R3...
- Common prefixes: mA (milliamp) = 0.001A, kOhm = 1000 Ohms
- US household voltage: 120V; European: 230V
- USB power: 5V at 0.5-3A; Car battery: 12V
Frequently Asked Questions
What is Ohm's Law?
Ohm's Law states that voltage (V) equals current (I) multiplied by resistance (R): V = I × R. It describes the relationship between voltage, current, and resistance in an electrical circuit. This fundamental law is essential for electrical engineering and circuit design.
How do I calculate current using Ohm's Law?
To find current, divide voltage by resistance: I = V / R. For example, with 12V and 4Ω: I = 12 / 4 = 3 Amps. Current is measured in Amperes (A) and represents the flow of electrical charge through a circuit.
What is electrical power?
Electrical power (P) is the rate of energy consumption, measured in Watts (W). It can be calculated as: P = V × I, P = I² × R, or P = V² / R. Power determines how much energy an electrical device uses or produces per second.
What is the relationship between voltage, current, resistance, and power?
The key formulas are: V = IR (Ohm's Law), P = VI, P = I²R, P = V²/R. Voltage is the "pressure" pushing current through a circuit. Resistance opposes current flow. Power is the energy consumed. All four are interconnected.
What units are used in Ohm's Law?
Voltage: Volts (V). Current: Amperes or Amps (A). Resistance: Ohms (Ω). Power: Watts (W). Common prefixes: milliamps (mA = 0.001A), kilohms (kΩ = 1000Ω), milliwatts (mW = 0.001W), kilowatts (kW = 1000W).