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標題:

A boy uses a convex lens to start a fire.

發問:

A boy uses a convex lens to start a fire.what is the distance between the lens and the leaves?

最佳解答:

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• 巳知長方形的四個頂點分別是A(-1,0),B(2,2),C(0,5)和D(a,b).

 

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The distance between the lens and the leaves is the focal length of the lens. Convex lens is converging lens, which can converge light towards the principle axis. The sunlight can be considered as light from infinity. By constructing a light-ray diagram, The light from infinity will be converged by the convex lens to the focal length of the lens. At the focal length of the lens, light is the most concentrated, which implies energy is most concentrated there. Therefore, if energy is sufficient, fire can be ignited to burn the leaves.

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