Chapter 33-Lenses and Optical Instruments: Thin Lens Equation, combinations of L

Question

Chapter 33-Lenses and Optical Instruments: Thin Lens Equation, combinations of Lenses, Selected Optical Instruments Problem 33.95 Part A A movie star catches a reporter shooting pictures of her at home. She claims the reporter was trespassing. To prove her point, she gives as evidence the film she seized. Her 1.80 m height is 7.50 mm high on the film, and the focal length of the camera lens was 230 mm How far away from the subject was the reporter standing? Express your answer using two significant figures. ?? Submit

Explanation / Answer

Object height Ho = 1.8 m and Image height Hi = 7.5 mm

Magnification M = Hi/Ho = 7.5mm / 1.8m = 4.17 x 10-3 = - di / do eqn (i).

where do and di are the object and image distance from the lens having focal length f = 230 mm. The negative sign comes from the convension.

From lens formula

1/di - 1/do = 1/f => 1/di - 1/do = 1/230 eqn (ii)

Solving equations (i) and (ii), we get

do = -55386 mm = 55 km and di = 231 mm

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