Question

The focal length of the objective of a telescope is 60 cm. To obtain a magnification of 20, the focal length of the eye piece should be:

Options

• 2 cm

• 3 cm

• 4 cm

• 5 cm

Answer 1

3 cm

Explanation:

In normal adjustment,

M = `"f"_0/"f"_"e"`

f_e = `"f"_0/20`

= `60/20`

= 3 cm