LEDs care more about amps
LEDs “choose” their own voltage drop; what saves them is limiting current. A tiny 5 mm LED is happy at ~20 mA but can fry above 30 mA.
Current matters
Ohm’s Law Calculator — Solve V, I, R, and P
Inputs & Units
Symbol: V
Symbol: I
Symbol: R
Symbol: P
Hints: Enter calculates · Esc clears · Values auto-scale (e.g., 0.002 A → 2 mA).
Results will appear here.
Formulas & Tips
Ohm’s law and power relationships:
- \( V = I \times R \)
- \( P = V \times I \)
- \( P = I^2 \times R \)
- \( P = \dfrac{V^2}{R} \)
Provide any two quantities (e.g., V and R). The calculator finds the other two and shows the steps.
Understanding Ohm’s Law
Ohm’s Law is one of the most important rules in electricity. It describes how voltage (V), current (I), and resistance (R) are related:
$$ V = I \times R $$
What the Symbols Mean
- V (Voltage): The “push” that moves charges through a circuit, measured in volts (V).
- I (Current): The flow of electric charge, measured in amperes (A).
- R (Resistance): How much a component resists the flow of current, measured in ohms (Ω).
- P (Power): The rate of using or producing energy, measured in watts (W).
The Ohm’s Law Triangle
A common study tip is the Ohm’s Law Triangle. Cover the value you want to find:
- \( V = I \times R \)
- \( I = \dfrac{V}{R} \)
- \( R = \dfrac{V}{I} \)
By remembering just the triangle, you can quickly rearrange the formula to solve for any missing value.
Adding Power to the Mix
Power (\(P\)) links to voltage and current:
$$ P = V \times I $$
With Ohm’s Law, we can also write:
- \( P = I^2 \times R \)
- \( P = \dfrac{V^2}{R} \)
These forms are useful for electronics design—like checking if a resistor can safely handle the power without overheating.
Real-Life Example
Suppose a 9 V battery is connected across a 1.5 kΩ resistor:
- Current: \( I = \dfrac{V}{R} = \dfrac{9}{1500} = 0.006 \,\text{A} = 6 \,\text{mA} \)
- Power: \( P = V \times I = 9 \times 0.006 = 0.054 \,\text{W} = 54 \,\text{mW} \)
So the resistor uses about 54 milliwatts of power—a very small amount, which is why this is a safe beginner circuit.
Why Ohm’s Law Matters
Engineers, electricians, and students use Ohm’s Law to:
- Design safe circuits.
- Calculate resistor values needed for LEDs or sensors.
- Estimate battery life in portable devices.
- Troubleshoot circuits when something isn’t working.
👉 Tip: Always keep track of units (V, A, Ω, W). Converting to base units first helps avoid mistakes.
5 Fun Facts about Ohm’s Law
Skin resistance swings wildly
Dry skin can be tens of kΩ; wet or broken skin can drop below 1 kΩ. Same voltage, very different currents—why safety standards focus on both volts and contact.
Human circuit
Batteries sag under load
Every source has an internal resistance. Pull a high current and the terminal voltage sags by \( V = I \times R_\text{internal} \)—that’s why flashlights dim on turbo.
Hidden resistor
Telegraph math
Early telegraph lines were limited by copper resistance; boosting voltage let signals travel farther, but too much arced relays. Ohm’s law literally set the range of 1800s messaging.
Vintage bandwidth
Heat is the silent cost
I²R losses turn current into heat in every wire. Halving current (with the same power) quarters resistive heating—why higher-voltage distribution wastes less.
Power loss