The power of sunlight reaching each square meter of the Earth's surface on a clear day in the tropics is close to 1 000 W. On a winter day in Manitoba, the power concentration of sunlight can be 100 W/m^2. Many human activities are described by a power per unit area on the order of 10^2 W/m^2 or less.

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The power of sunlight reaching each square meter of the Earth's surface on a clear day in the tropics is close to 1 000 W. On a winter day in Manitoba, the power concentration of sunlight can be 100 W/m2. Many human activities are described by a power per unit area on the order of 102 W/m2 or less.

(a) Consider, for example, a family of four paying $66 to the electric company every 30 days for 619 kWh of energy carried by electrical transmission to their house, which has floor dimensions of 13.0 m by 9.50 m. Compute the power per unit area used by the family.
 W/m2

(b) Consider a car 2.23 m wide and 4.90 m long traveling at 55.0 mi/h using gasoline having "heat of combustion" 44.0 MJ/kg with fuel economy 25.0 mi/gal. One gallon of gasoline has a mass of 2.54 kg. Find the power per unit area used by the car.
 W/m2

(c) Explain why direct use of solar energy is not practical for running a conventional automobile.



(d) What are some uses of solar energy that are more practical?

 

asked Mar 27, 2012 in Physics by Gummmys ~Expert~ (1,105 points)
    

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