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A family uses $8 \mathrm{~kW}$ of power. (a) Direct solar energy is incident on the horizontal surface at an average rate of $200 \mathrm{~W}$ per square meter. If $20 \%$ of this energy can be converted to useful electrical energy, how large an area is needed to supply 8 kW?(b) Compare this area to that of the roof of a typical house.
A family uses $8 \mathrm{~kW}$ of power. (a) Direct solar energy is incident on the horizontal surface at an average rate of $200 \mathrm{~W}$ per square meter. If $20 \%$ of this energy can be converted to useful electrical energy, how large an area is needed to supply 8 kW?(b) Compare this area to that of the roof of a typical house.
CBSE | Class 11 | NCERT | Physics | Work, Energy, and Power
A family uses $8 \mathrm{~kW}$ of power. (a) Direct solar energy is incident on the horizontal surface at an average rate of $200 \mathrm{~W}$ per square meter. If $20 \%$ of this energy can be converted to useful electrical energy, how large an area is needed to supply 8 kW?(b) Compare this area to that of the roof of a typical house.

(a) Power used by family is given as $p=8 \mathrm{KW}=8000 \mathrm{~W}$

Solar energy received per square metre is given as $200 \mathrm{~W} / \mathrm{m}^{2}$

Percentage of energy converted to useful electrical energy is given as $20 \%$

As solar energy is incident at a rate of $200 \mathrm{Wm}^{-2}$, the area required to generate the desired energy will be $A$

Useful electrical energy produced per second can be calculated as,

$=(20 / 100) \mathrm{A} \times 200=8000$

$A=4000 \mathrm{~W} / 200 \mathrm{Wm}^{-2}=200 \mathrm{~m}^{2}$

(b) $14 \mathrm{~m} \times 14 \mathrm{~m}$ is the area needed is comparable to the roof of a large house of dimension.

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