At steady-state, a porch light with a 100 W incandescent bulb produces 97.8 W of heat energy, the rest of its output being visible light.a) What is the efficiency of the light bulb? (use the definition from the class notes)b) How much energy does the bulb consume annually if it is on for an average of 8 hours per day (in kWh)?c) What is the annual cost of the energy at a rate of $0.08/kWh?

Respuesta :

Answer:

a

The efficiency is  =97.8%

b

The Energy consumed is [tex]=10512*10^5 J[/tex]

c

The annual cost is  = $23.36

Explanation:

from the question we are given

        Power supplied = 100 W

        Power Produced  = 97.8 W

  The Efficiency can be  evaluated as [tex]\eta = \frac{Power \ Produced}{Power \ Supplied}[/tex]

                                                                [tex]\eta = \frac{97.8}{100}*\frac{100}{1}[/tex]

                                                                    =97.8%

To obtain the energy consumed  in a year

     We have to known that

             1 year  = 365 days

           Total hours  = 8 * 365 = 2920 hours [Since 8 hours is used in one day]

           and the 2920 hours obtained = (292× 3600) = 10,512,000 sec

 Energy = Power ×  Time

              =  (100 × 10512000) W.sec

              [tex]=10512*10^5 J[/tex]

Generally

                 [tex]1Kwh = 36*10^5 J\\[/tex]

So ,Energy in (Kwh)   [tex]= \frac{10512*10^5}{36*10^5}[/tex]

                                    [tex]= 292 Kwh[/tex]

Given that the rate should be  $0.08/kWh

           The Annual cost would be  

                                                    [tex]=292 Kwh * \frac{0.08}{Kwh}[/tex]

                                                     [tex]= 23.36[/tex]

Answer:

(a) efficiency = 2.2495%

(b) Total power consumption

for a whole year = 292kwh

(c) cost = $23.36/kwh

Explanation:

Let He be the heat emitted

Pr be the power rating

and Hl Heat emitted in light

Hl = Pr - He = 100-97.8 = 2.2w

(a) Efficiency = 2.2/97.8 x 100 = 2.2495%

(b) Total hours of consumption for a year is = 8 x 365days = 2920hours

Total power consumption for a year is = 2920 x 100 = 292, 000w = 292kwh

(c) If one 1 kwh costs $0.08

then 292kwh will cost 0.08. x 292 = $23.36/kwh