## Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (4th Edition)

The focal length objective is $~~2.0~mm$
We can find the focal length objective: $M = -\frac{L}{f_{obj}}\cdot \frac{25~cm}{f_{eye}}$ $f_{obj} = -\frac{L}{M}\cdot \frac{25~cm}{f_{eye}}$ $f_{obj} = -\frac{20~cm}{-500}\cdot \frac{25~cm}{5.0~cm}$ $f_{obj} = 0.20~cm$ $f_{obj} = 2.0~mm$ The focal length objective is $~~2.0~mm$