A 100 W lightbulb is plugged into a standard 120 V outlet. How much does it cost

Question

A 100 W lightbulb is plugged into a standard 120V outlet. How much does it cost per month (30 days) toleave the light turned on continuosly?
1. Assume electrical energy costs 6.5/kWh. (Enter dollarswith no unit) 2. What is the resistance of thebulb? 3. What is the current in thebulb? A 100 W lightbulb is plugged into a standard 120V outlet. How much does it cost per month (30 days) toleave the light turned on continuosly?
1. Assume electrical energy costs 6.5/kWh. (Enter dollarswith no unit) 2. What is the resistance of thebulb? 3. What is the current in thebulb?

Explanation / Answer

1. cost = 0.1kW * 30 * 24h * 6.5 / kWh= 468 cents = 4.68 $ 2.   P = V2 / R        ==> R = V2 / P= 120 * 120 / 100 = 144 3. I = V / R = 120 / 144 = 0.833

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