Question
A Galilean telescope is 27cm long when focused to form an image at infinity. If the objective has a focal length of 30cm, what is the focal length of the eyepiece?
✓
Answer
For the given Galilean telescope, (When the image is formed at infinity)
f0 = 30cm, L = 27cm
Since L = f0 - |fe|
[Since, concave eyepiece lens is used in Galilean Telescope]
⇒ fe = f0 - L = 30 - 27 = 3cm
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