Question

. Draw a labelled ray diagram of an
astronomical telescope, forming the
image at infinity.
An astronomical telescope uses two
lenses of powers 10D and 1D.
State with reason, which lens is preferred
of objective and eyepiece.​

Answer 1

Answer:

An astronomical telescope uses two lenses of power 10 dioptre and 1 diopter. If the final image of a distant object is formed at infinity, calculate the length of the telescope.

Given,

Power of 1 lens, P1 = 10 Dioptre

Power of 2nd lens, P2 = 1 Dioptre

Focal length, f1 = 1 over straight P subscript 1 space equals space 1 over 10 space equals space 0.1 space m space left parenthesis space f o r space e y e p i e c e right parenthesis

Focal length, f2 = 1 over straight P subscript 2 space equals space 1 over 1 equals 1.0 space m (objective)

Length of the telescope, L = fo + fe

= 1.0 + 0.1

= 1.1 m