# Optics – Image formation (lenses)

**1. The problem statement, all variables and given/known data**

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?

**2. Relevant equations**

$$\dfrac{1}{d_0}+\dfrac{1}{d_i}=\dfrac{1}{f}$$

**3. The 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 the ##s_i=17cm (>0)##

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

$$\dfrac{1}{d_0}+\dfrac{1}{17}=- \dfrac{1}{48}$$

And doing the calculations, it comes down to:

$$s_0=-12.55$$

However, the solutions say the solution is ##s_0=26.3##. One can get that if we take ##s_i## to be negative, which is wrong, in my opinion. (?)

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

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