8. a) A bracken fern spore produces an image that is 7.5 cm tall when placed bef

Question

8. a) A bracken fern spore produces an image that is 7.5 cm tall when placed before a converging lens of focal length 5.0 cm. If the spore's true height is 1.5 mm, how far from the lens was it placed? b) A bracken fern spore produces an image that is 7.5 cm tall when placed before a converging lens of focal length 6.0 cm. If the spore's true height is 1.5 mm, how far from the lens was its image? c) A lens with an unknown focal length forms an image of an object that is 12 cm away from the lens, inverted, and a factor of 3.0 larger in size than the object. Where is the object located?

Explanation / Answer

We use 1/f=i/u + 1/v Given v/u=magnification=75/1.5 = 50 v=50u So 1/5 = 1/u + 1/50u = 51/50u So u = 51/10 = 5.1 cm Hope you like my awesome yet short method :)

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