With an object at the focal point of a magnifying glass, the magnification is given by m = (25 cm) / f (Eq. 25.4). According to this equation, the magnification could be increased indefinitely by using lenses with shorter focal lengths. Why, then, are compound microscopes needed?
Answer to relevant QuestionsIf you are given two lenses with different focal lengths, how would you decide which should be used as the objective and which should be used as the eyepiece for a telescope? Explain. An eyeglass lens with a power of + 2.8 D allows a far-sighted person to read a book held at a distance of 25 cm from her eyes. At what distance must she hold the book to read it without glasses? A person is prescribed with contact lenses that have powers of – 3.0 D. What type of lenses are these? What is the lenses’ focal length? If a magnifying glass gives an angular magnification of 1.5 x when viewed with relaxed eyes, what is the power of the lens? A specimen is 5.0 mm from the objective of a com-pound microscope that has a lens power of + 250 D. What must be the magnifying power of the eyepiece if the total magnification of the specimen is – 100 x?
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