Physics

Problem

The objective of a refracting telescope has focal length

80\,\text{cm}

and the eyepiece has focal length

4\,\text{cm}

. For normal adjustment, the magnifying power

M

and the tube length

L

respectively are a)

M=+20,\;L=84\,\text{cm}

M=-20,\;L=84\,\text{cm}

M=-20,\;L=76\,\text{cm}

M=-16,\;L=80\,\text{cm}