Electricity โ Ohm's Law, Power & Energy
Calculate voltage, current, resistance, power, energy, and electricity costs. Complete circuit analysis with Ohm's Law and safety recommendations.
Why This Scientific Calculation Matters
Why: Understanding voltage, current, and resistance is essential for circuit design, safety, and energy cost estimation.
How: Select calculation type (Ohm's Law, Power, Energy, Cost), enter known values, and leave one blank to solve.
- โV = IR
- โP = VI = IยฒR = Vยฒ/R
- โ100mA can be lethal
โก Quick Examples โ Click to Load
Calculation Mode
Input Values
๐งช Scientific Discoveries
Lightning: ~300 million V, 30,000 A
โ NOAA
US household: ~10,500 kWh/yr
โ EIA
Phantom power: $100โ200/yr
โ DOE
๐ Key Takeaways
- โข Ohm's Law (V = IR) is the foundation of all circuit analysis โ know any two and solve for the third
- โข Power has three equivalent forms: P = VI = IยฒR = Vยฒ/R
- โข Current as low as 100mA (0.1A) can be lethal to humans โ always respect electricity
- โข A device's wattage ร hours of use ร electricity rate = your cost
- โข Wire gauge must match current โ undersized wires cause fires. Always follow NEC/IEC standards
๐ก Did You Know?
๐ How Electrical Circuits Work
Understanding electricity starts with three fundamental quantities: Voltage (electrical pressure), Current (flow of charge), and Resistance (opposition to flow).
Ohm's Law: The Water Analogy
Think of voltage as water pressure, current as flow rate, and resistance as pipe width. Higher pressure (voltage) or wider pipes (lower resistance) means more flow (current).
Power: The Rate of Energy Use
Power (watts) tells you how fast energy is consumed. A 100W bulb uses energy 10ร faster than a 10W LED. Power = Voltage ร Current.
Energy & Cost: What You Pay For
You pay for energy (kWh), not power. A 1000W heater running for 1 hour uses 1 kWh. At $0.16/kWh, that costs $0.16. Running it 8 hours/day for a month: $38.40.
๐ Key Formulas
๐ฏ Expert Tips
๐ก Energy Savings
Replace a 60W incandescent with a 9W LED. Running 8hrs/day saves ~$15/year per bulb. Multiply by all bulbs in your home!
๐ก Circuit Protection
Always use fuses or breakers rated slightly above your circuit's normal current. A 20A breaker protects 12 AWG wire from overheating.
๐ก Series vs Parallel
Series: resistances add (R_total = R1 + R2). Parallel: reciprocals add (1/R_total = 1/R1 + 1/R2). Most home outlets are wired in parallel.
๐ก Phantom Loads
Use a power strip with an on/off switch for entertainment centers. TVs, game consoles, and chargers draw 5-25W even when "off."
โ๏ธ Common Appliance Power Reference
| Appliance | Watts | Current (120V) | Monthly Cost* |
|---|---|---|---|
| LED Bulb | 9W | 0.075A | $0.35 |
| Laptop | 50-100W | 0.42-0.83A | $1.92-$3.84 |
| Desktop PC | 200-500W | 1.67-4.17A | $7.68-$19.20 |
| Refrigerator | 100-400W | 0.83-3.33A | $3.84-$15.36 |
| Microwave | 600-1200W | 5-10A | $2.88-$5.76 |
| Space Heater | 1500W | 12.5A | $57.60 |
| EV Charger (L2) | 7200W | 30A | $34.56/charge |
| Clothes Dryer | 4000-5000W | 33-42A | $19.20-$24.00 |
*Based on 8 hrs/day, $0.16/kWh. EV charger based on single full charge (40kWh).
โ Frequently Asked Questions
What is Ohm's Law?
Ohm's Law (V = IR) states that voltage across a conductor is proportional to the current flowing through it, with resistance as the constant of proportionality. Published by Georg Simon Ohm in 1827.
How much current is dangerous?
Current as low as 1mA can be felt, 10mA causes painful shock, and 100mA (0.1A) across the heart can be fatal. Voltage above 50V is generally considered hazardous. Always use proper insulation and grounding.
What wire gauge do I need?
Wire gauge depends on current: 14 AWG for up to 15A, 12 AWG for 20A, 10 AWG for 30A. Always follow local electrical codes (NEC in the US). Undersized wires overheat and cause fires.
How do I reduce my electricity bill?
Top strategies: Switch to LED lighting (saves ~75% vs incandescent), use smart power strips, upgrade to Energy Star appliances, seal air leaks, set thermostat 2ยฐF lower in winter / higher in summer. Typical savings: $200-500/year.
What is the difference between AC and DC?
DC (Direct Current) flows in one direction โ used in batteries, electronics, solar cells. AC (Alternating Current) reverses direction 50-60 times per second โ used in power grids because it transforms voltage efficiently for long-distance transmission.
Why do different countries use different voltages?
The US uses 120V/60Hz, while most of Europe uses 230V/50Hz. Higher voltage allows thinner wires and less power loss, but 120V was adopted early in the US for safety with existing Edison-era equipment.
๐ Electricity by the Numbers
๐ Official Data Sources
โ ๏ธ Disclaimer: This calculator provides estimates for educational purposes. Real circuits involve temperature effects, AC impedance, wire length, and other factors. Always consult a licensed electrician for actual wiring projects. Wire gauge recommendations are general guidelines โ follow your local electrical code (NEC, IEC) for all installations.
โ ๏ธFor educational and informational purposes only. Verify with a qualified professional.