Advertisements
Advertisements
प्रश्न
A family uses 8 kW of power.
- 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?
- Compare this area to that of the roof of a typical house.
Advertisements
उत्तर १
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 × 10^3)/ 40` = 200 m2
(b) The area necessary for a solar plate to produce 8 kW of electricity closely matches the roof area of a building that measures 14 m × 14 m. (≈ `sqrt200`).
उत्तर २
(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 = `(40000 "W")/(200 "Wm"^2)` =200 m2
(b) The area needed is camparable to roof area of a large sized house.
APPEARS IN
संबंधित प्रश्न
A pump on the ground floor of a building can pump up water to fill a tank of volume 30 m3 in 15 min. If the tank is 40 m above the ground, and the efficiency of the pump is 30%, how much electric power is consumed by the pump?
The blades of a windmill sweep out a circle of area A.
- If the wind flows at a velocity v perpendicular to the circle, what is the mass of the air passing through it in time t?
- What is the kinetic energy of the air?
- Assume that the windmill converts 25% of the wind’s energy into electrical energy, and that A = 30 m2, v = 36 km/h and the density of air is 1.2 kg m–3. What is the electrical power produced?
Rajan exerts a force of 150 N in pulling a cart at a constant speed of 10 m/s-1. Calculate the power exerted.
Power P= ............ /time taken.
The S.I. unit of power is ..........
Match the following
| column A | Column B |
| A stone at a height | power |
| A Moving ball | joule |
| Energy | work done in 1 s |
| Power | potential energy |
| Watt | kinetic energy |
Name the physical quantity which is measured in calorie. How is it related to the S.I. unit of the quality?
Differentiate between watt and watt hour.
Choose one or more correct alternatives.
Power is a measure of the ______.
- The rapidity with which work is done.
- Amount of energy required to perform the work.
- The slowness with which work is performed.
- Length of time.
A wind-powered generator converts wind energy into electric energy. Assume that the generator converts a fixed fraction of the wind energy intercepted by its blades into electrical energy. For wind speed v, the electrical power output will be proportional to ______
Two equal masses m1 and m2 are moving along the same straight line with velocities 5 ms-1 and -9 ms-1 respectively. If the collision is elastic, then calculate the velocities after the collision of m1 and m2, respectively.
An engine develops 20 kW power. How much time will it take to lift a mass of 200 kg to a height of 50 m? (g = 10 m/s2)
Water falls from a height of 60 m at the rate of 15 kg/s to operate a turbine. The losses due to frictional force are 10% of the input energy. How much power is generated by the turbine? (g = 10 m/s2)
The average work done by a human heart while it beats once is 0.5 J. Calculate the power used by heart if it beats 72 times in a minute.
A man is throwing bricks of mass 2 kg onto a floor from a height of 2 m. Bricks reach the floor at a speed `2sqrt(10)` m/s. Man throws 10 bricks in a minute. If the power of man is W watt then `3/10` W is equal to ______ W.
Calculate the power spent by a crane while lifting a load of mass 2000 kg, at velocity of 1.5 ms-1. (g = 10 ms-2)
