Electrical & Engineering5 min read
How to Calculate kWh Usage of Appliances at Home
Power in kW times hours gives kWh. A 75 W fan on 10 hours a day uses 22.5 units a month; a household of four appliances reaches about 94 kWh.
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- Electrical & Engineering5 min read
How to Choose a Resistor for an LED
R = (supply − LED forward voltage) ÷ current. For a 9 V supply, a 2 V LED and 20 mA, that is 350 Ω; a 0.25 W part is enough.
- Electrical & Engineering4 min read
How Much Energy Does Switching to LED Save?
Swapping a 100 W bulb for a 20 W LED used 6 hours a day saves 14.4 kWh in 30 days. Learn the formula, the rupee value and a payback sum for a few bulbs.
- Electrical & Engineering4 min read
Lighting Power Density in W/m² Explained
20 fixtures of 24 W over an 80 m² room make 6 W/m² of lighting power density. See the formula, how it links to lux, and how to compare spaces fairly.
- Electrical & Engineering5 min read
Ohm's Law: V = I × R and Its Power Cousins
Voltage equals current times resistance: 2 A through 6 Ω drops 12 V. Learn the three rearrangements, power formulas and an LED resistor worked example.
- Electrical & Engineering5 min read
RC Time Constant: Charging, 63% and 5τ
The RC time constant is τ = R × C. After one τ a charging capacitor reaches 63.2% of supply, and about 99.3% after 5τ. 10 kΩ × 100 µF = 1 s.
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