CBSE (Science) Class 11CBSE
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# A Family Uses 8 Kw of Power. (A) Direct Solar Energy is Incident on the Horizontal Surface at an Average Rate of 200 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 (Science) Class 11 - Physics

#### Question

A family uses 8 kW of power. (a) Direct solar energy is incident on the horizontal surface at an average rate of 200 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.

#### Solution 1

(a) Power used by the family, P = 8 kW = 8 × 103 W

Solar energy received per square metre = 200 W

Efficiency of conversion from solar to electricity energy = 20 %

Area required to generate the desired electricity = A

As per the information given in the question, we have:

8 × 103 = 20% × (A × 200)

= (20 /100) × A × 200

∴ A = 8 × 103 / 40  =  200 m2

(b) The area of a solar plate required to generate 8 kW of electricity is almost equivalent to the area of the roof of a building having dimensions 14 m × 14 m. (≈ sqrt200).

#### Solution 2

(a) Power used by family, p = 8 KW = 8000 W

As only 20% of solar energy can be converted to useful electrical energy, hence, power

8000 W to be supplied by solar energy = 8000 W/20 = 40000 W

As solar energy is incident at a rate of 200 Wm-2, hence the area needed

A=4000 W/200 Wm-2 =200 m2

(b) The area needed is camparable to roof area of a large sized house.

Is there an error in this question or solution?

#### APPEARS IN

NCERT Solution for Physics Textbook for Class 11 (2018 to Current)
Chapter 6: Work, Energy and Power
Q: 23 | Page no. 137
Solution A Family Uses 8 Kw of Power. (A) Direct Solar Energy is Incident on the Horizontal Surface at an Average Rate of 200 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 Concept: Power.
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