Compact fluorescent bulbs are much more efficient at producinglight than are ordinary incandescent bulbs. They initially costmore, but last far longer and use much less electricity. Accordingto one study of these bulbs, a compact bulb that produces as muchlight as a 100W incandescent bulb uses only 23W of power. Thecompact bulb lasts 10,000 hours, on average, and costs $5.00,whereas the incandescent bulb costs only $0.75, but lasts just 750hours. The study assumed that electricity cost $0.08/(kW*hr) andthat the bulbs were on for 4 hours per day. (Careful with kW*hrcalculations it is NOT kW/hr. Electric companies charge for energywhich is power*time)

(a) What is the total cost (including the price ofthe bulbs) to run each type of bulb for 3 years?

(b) How much do you save over 3 years if youuse a compact fluorescent bulb? (Don’t forget that compactbulbs should not be thrown out in the trash but recycled!)

c)What is the resistance of a "100W"fluorescent bulb? (Remember the actual rating is only 23W of powerfor a 120V circuit)

Respuesta :

Answer:

(a) Total cost to run a compact bulb is $13.0592

Total cost to run an incandescent bulb is $39.54

(b) $26.4808

(c) 2721.7 ohms

Explanation:

In 3 years, each of the bulbs would be on for 4380 hours (4 hours/day)

(a) Compact bulbs last 10,000 hours

Power rating = 23 W = 23/1000 = 0.023 kW

Energy consumed in 3 years = 0.023×4380 = 100.74 kWh

Electricity cost = $0.08/kWh × 100.74 kWh = $8.0592

Total cost = $5+$8.0592 = $13.0592

Incandescent bulbs last 750 hours

In 3 years, about 6 incandescent bulbs would be bought = 6×$0.75 = $4.5

Power rating = 100 W = 100/1000 = 0.1 kW

Energy consumed in 3 years = 0.1×4380 = 438 kWh

Electricity cost = $0.08/kWh × 438kWh = $35.04

Total cost = $4.5+$35.04 = $39.54

(b) Savings = $39.54 - $13.0592 = $26.4808

(c) 23 W has 120 V circuit

100W would have 100×120/23 = 521.7 V

R = V^2/P = 521.7^2/100 = 2721.7 ohms