10. (a) A circuit provides a maximum current of 20.0 A at an operating voltage o

Question

10. (a) A circuit provides a maximum current of 20.0 A at an operating voltage of 1.20 x 102 v i. How many 75 W light bulbs can operate with this voltage source? . At $0.120 per kWh, how much does it cost to operate these bulbs for 8.00 hours? (b) In Springville, Utah, electricity costs $0.09 per kWh. What is the annual cost for electricity to power a lamp-post for 5.00 hours per day with i. a 100 watt incandescent light bulb ii. an energy efficient 15-watt A21 LED light bulb that produces the same amount of light? (e) If a typical incandescent bulb costs $0.89 and lasts for about a year; a typical energy efficient A21 LED costs about $6.99 and lasts for about 25, 000 hours of operation What is the savings of switching to the LED bulb? Estimate how many lights posts we have in the US and how much it would save the nation (assume the rates of Springville, UT.)

Explanation / Answer

(a)(i) Total power delivered, P=Vi

=1.2*10^2*20= 2400 W

Let n be the number of bulbs required each of power consumption 75 W

P = n(75W)

n = 2400÷75

= 32 bulbs

(ii) The energy consumption by the bulb is,

E = Pt

= 2400(8)÷1000

= 19.2 kWh

The cost to operate the bulbs

Cost = 19.2(0.120)

= $2.304

  

  

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