An object is placed to the left of a lens, and a real image isformed to the righ

Question

An object is placed to the left of a lens, and a real image isformed to the right of the lens. The image is inverted relative tothe object and is one-half the size of the object. The distancebetween the object and the image is 47.9cm. (a) How far from the lens is the object? do ---Select---no unitscm^-1cm
(b) What is the focal length of the lens? f ---Select---no unitscm^-1cm (a) How far from the lens is the object? do ---Select---no unitscm^-1cm
(b) What is the focal length of the lens? f ---Select---no unitscm^-1cm do ---Select---no unitscm^-1cm

Explanation / Answer

   let the object distance be'do' and image distance be'di'.    Given         do   +   di   =   47.9   cm    magnification      m   =   di/ do   =   himage/hobject        (magnitudeonly)     di/ do   =   1/2       di   =   0.5 * do    a.     do   +   0.5* do   =   47.9          objectdistance   do   =   47.9/ 1.5                                              =   31.93   cm    a.     do   +   0.5* do   =   47.9          objectdistance   do   =   47.9/ 1.5                                              =   31.93   cm    b.   di   =   0.5* do                =   0.5* 31.93                =   15.97   cm       Since do is tothe left of lens, it will be taken as negative.       1/f   =   1/di   -   1/do           1/f   =   1/15.97   -   1/(-31.93)       f   =   15.97* 31.93 / (31.93 + 15.97)          =   10.65   cm           1/f   =   1/15.97   -   1/(-31.93)       f   =   15.97* 31.93 / (31.93 + 15.97)          =   10.65   cm          

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