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21_Ch 25 College Physics ProblemCH25 Optical Instruments

# 21_Ch 25 College Physics ProblemCH25 Optical Instruments -...

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Optical Instruments 357 25.47 Removing air from the cell alters the wavelength of the light passing through the cell. Four fringe shifts will occur for each additional wavelength fitted into the length of the cell. Therefore, the number of fringe shifts that occur as the cell is evacuated will be ( ) 4 4 4 shifts air n air L L L L L N n n λ λ λ λ λ = = = ( 1 or ) ( ) 2 9 4 5.00 10 m 1.000 29 1 98.3 590 10 m shifts N × = × = 98 complete shifts 25.48 (a) Since this eye can already focus on objects located at the near point of a normal eye (25 cm), no correction is needed for near objects. To correct the distant vision, a corrective lens (located 2.0 cm from the eye) should form virtual images of very distant objects at 23 cm in front of the lens (or at the far point of the eye). Thus, we must require that when 23 cm q = − p → ∞ . This gives 1 1 1 0 4.3 di P f p q = = + = − 1 0.23 m = + opters (b) A corrective lens in contact with the cornea should form virtual images of very
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