A large body of lava is slowly cooling. Its surface is at 723 K. How much energy
ID: 1333107 • Letter: A
Question
A large body of lava is slowly cooling. Its surface is at 723 K. How much energy does each m2 of its surface radiate into the environment at 300 K? Assume e = 1.
A) 8.1kW
B)2.3KW
C)5.2KW
D) 15KW
Today electric vehicles get about 4.7 miles per kwh. IF my round trip commute is 25 miles how many m^2 of solar panels do I need to provide energy in 4.0 hours. Asssume the panels are exposed to the sun near noon and have an efficiency of 12% (solar radiation is 1.3 KW/m^2)Explain your answer
A) 11m^2
B) 8.5 m^2
C) 22m^2
D )18m^2
E) 14m^2
Explanation / Answer
1) D) 15KW
According to stefan-Boltzman's law
Energy radiated per unit area per unit time = sigma*(T1^4 - T2^4)
= 5.67*10^-8*(723^4 - 300^4)
= 15000 W
= 15 kW
2) B) 8.5 m^2
Energy required for round trip, E = 25/4.7
= 5.32 kWh
= 5.32*3.6*10^6
= 1.915*10^7 J
Let N no of m^2 solar panels needed.
Apply, E = N*e*Intensit_sun*t
N = E/(e*Intensity_sun*t)
= 1.915*10^7/(0.12*1.3*10^3*4*60*60)
= 8.5 m^2
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