Question

Since \[D\] is about 25 cm, what focal length of convex lens is needed to achieve a magnification of six with a simple microscope?

Options

• \[f = 5\ \text{cm}\]

• \[f = 25\ \text{cm}\]

• \[f = 15\ \text{cm}\]

• \[f = 2.5\ \text{cm}\]

Answer 1

Using \[m = \left(1 + \frac{D}{f}\right)\] with \[m = 6\] and \[D = 25\ \text{cm}\]: \[6 = 1 + \frac{25}{f}\], so \[\frac{25}{f} = 5\], giving \[f = 5\ \text{cm}\]. Thus, a convex lens of focal length 5 cm is needed for a magnification of six.