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