The objective of a refracting telescope has focal length and the eyepiece has focal length

PHYSICS · Single correct · CBSE · Physics · Ray Optics and Optical Instruments · Ray Optics and Optical Instruments

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}

(b)

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

(c)

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

(d)

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