First slide

Ray optics

Question

Find the length of a telescope for which it is known that it has an objective lens of focal length 144 cm and an eye piece of focal length 6 cm.

Easy

A

0.75 m
B

1.38 m
C

1.0 m
D

1.5 m

Solution

The separation between the objective and the eye piece = Length of the telescope, tube f = f₀ + f_e
Here, $f_{0} = 144 cm = 1.44 m, f_{e} = 6.0 cm = 0.06 m$
$∴ f = 1.44 + 0.06 = 1.5 m$

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