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3.1 WAVES

P31 015

The diameter of the Moon is 2.48x10⁶ m and its distance from the Earth is 3.84x10⁸ m. What is the focal length of a lens required to produce a lunar image 20 mm in diameter?

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Solution

Knowledge thin lenses

Thin lens equation

Magnification

Since the image of a distant object is formed at the focus, the focal length is simply equal to the image distance .