wiz-icon
MyQuestionIcon
MyQuestionIcon
1
You visited us 1 times! Enjoying our articles? Unlock Full Access!
Question

The focal lengths of the lenses of an astronomical telescope are 50 cm and 5 cm. The length of the telescope when the image is formed at the least distance of distinct vision is

A
45 cm
No worries! We‘ve got your back. Try BYJU‘S free classes today!
B
55 cm
No worries! We‘ve got your back. Try BYJU‘S free classes today!
C
2756cm
No worries! We‘ve got your back. Try BYJU‘S free classes today!
D
3256cm
Right on! Give the BNAT exam to get a 100% scholarship for BYJUS courses
Open in App
Solution

The correct option is D 3256cm
The length of the telescope, LD=f0+ue, as the objective forms the image at its focus, as the rays are from infinity, and this image acts as the object for the eyepiece.
Now, using lens formula, and using the fact that the eyepiece forms image at near point, that is v=D(=25cm):
1f=1v1u.
Applying sign convention, 1ue=1D1fe.
Or, considering only the modulus, ue=feDfe+D.
Therefore, LD=f0+ue=f0+feDfe+D=50+5×25(5+25)=3256cm.

flag
Suggest Corrections
thumbs-up
0
Join BYJU'S Learning Program
similar_icon
Related Videos
thumbnail
lock
Telescope
PHYSICS
Watch in App
Join BYJU'S Learning Program
CrossIcon