Does it take a lot of water to light a light bulb? That depends on its wattage and how long it glows. |
Refer to the following information for the next five questions.
In this practice page, you are to calculate the mass and volume of water that falls over a 10-rn high dam to keep a 100-W light bulb glowing for 1 year.
First, calculate how many joules are required to keep the bulb lit for 1 year. |
But this assumes 100% efficiency. A hydroelectric plant is typically 20% efficient. This means only 1 part in 5 of the PE of the falling water ends up as electricity. So the mass above must be multiplied by 5 to get the actual amount of water that must fall to keep the 100-W bulb lit. |
For comparison, an Olympic-size swimming pool holds about 4000 m3 of water. How many such "poolfuls" of water are required to keep a 100-W bulb lit for one year?
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Does it take a lot of water to light a light bulb? To light a city full of light bulbs? Now you have a better idea!