Explanation:
a) To calculate the total KWH (kilowatt-hours) used by the lights in one year, we can use the following formula:
Total KWH = (Watts used per hour x Hours per day x Days per year) / 1000
Plugging in the given values, we get:
Total KWH = (400 x 4 x 365) / 1000 = 584 KWH per year
Therefore, the electric lights would use 584 KWH per year.
b) If using a fluorescent bulb instead of an incandescent bulb saves 60 W per hour, then the new wattage used per hour would be:
New wattage = 400 - 60 = 340 W per hour
Using the same formula as before, we can calculate the new total KWH used per year:
Total KWH = (340 x 4 x 365) / 1000 = 496.4 KWH per year
Therefore, using a fluorescent bulb instead of an incandescent bulb would save (584 - 496.4) = 87.6 KWH per year.
c) A fluorescent bulb that costs $18 but lasts for 10 years is likely to be a wise investment over incandescent bulbs, even though the upfront cost is higher. This is because the fluorescent bulb would consume less electricity and save money on electricity bills in the long run, as we saw in part b.
To calculate the cost savings over 10 years, let's assume that electricity costs $0.12 per KWH. The total cost of using the incandescent bulbs over 10 years would be:
Total cost = 584 KWH per year x 0.12 dollars/KWH x 10 years = $700.80
The cost of using the fluorescent bulb over 10 years would be:
Cost of bulb + Total electricity cost = $18 + (496.4 KWH per year x 0.12 dollars/KWH x 10 years) = $99.41
Therefore, the total cost savings over 10 years would be $700.80 - $99.41 = $601.39.
Since the fluorescent bulb costs less over the long run, it would be a wise investment over incandescent bulbs. Additionally, the longer lifespan of the fluorescent bulb means that it would need to be replaced less frequently, which could also save money on replacement costs.