Sunday, 4 September 2016

homework and exercises - Image formation (lenses)



I have a question regarding image formation by lenses. It is the following:



A lense with a focal length of 48.0cm forms an image 17.0cm to the right of the lense. Where is the object positioned?


My attempt at a solution:


Well, since the focal length is negative, we know that the lense is divergent (concave). The problem statement says that the image is to the right of the lense, so si=17cm(>0)


We can compute the position of the object by using the formula below:


1d0+1di=1f


Changing what we know for the values, we get:


1d0+117=148


And doing the calculations, it comes down to:


s0=12.55


However, the solutions say the solution is s0=26.3. One can get that if we take si to be negative, which is wrong, in my opinion. (?)



So, why am I wrong? Or am I correct?




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