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

A telescope has an objective lens of focal length 200 cm and an eyepiece with focal length 2 cm. If this telescope is used to see a 50 m tall building at a distance of 2 km, what is the height of the image of the building formed by the objective lens ?

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

The correct option is C 5 cm
Given,
Focal length of objective lens, f0=200 cm

Focal length of eye-piece, fe=2 cm

Height of building, h=50 m and its distance is 2 km.


Since, the object distance is very large compared to focal length of the objective lens. So, the image of the building will form near the focal length of the objective.

h0=50 m, u=2 km=2000 m

v=f0=200 cm=2 m

Let the height of the image be hi.

Now, we know magnification, m=vu=hih0

22000=hi50

hi=120 m=5 cm

Hence, (C) is the correct answer.
Key point: Whenever object distance is large compared to focal length of the lenses, the object is considered to be at infinity.

flag
Suggest Corrections
thumbs-up
5
Join BYJU'S Learning Program
similar_icon
Related Videos
thumbnail
lock
Lateral Magnification
PHYSICS
Watch in App
Join BYJU'S Learning Program
CrossIcon