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

An opera glass has a length of 30 cm and its magnifying power is 5 when used to view distant objects. Calculate the focal length of its lenses.

A
5cm and 25cm
Right on! Give the BNAT exam to get a 100% scholarship for BYJUS courses
B
7cm and 35cm
No worries! We‘ve got your back. Try BYJU‘S free classes today!
C
6cm and 30cm
No worries! We‘ve got your back. Try BYJU‘S free classes today!
D
8cm and 4cm
No worries! We‘ve got your back. Try BYJU‘S free classes today!
Open in App
Solution

The correct option is A 5cm and 25cm
For an opera glass
length (L)=f0+fe magnifying power =f0fe
where fo = focal length of objective lens.
fe = focal length of eye piece.
Here
f0+fe=301f0fe=5f0=5fe2
substitute equation (2) in (1) .
f0+fe=303fe+fe=306fe=30Fe=5 cm
By (2)
f0=5fef0=5(5)f0=25 cm
so focal length of its lenses =5 cm and =25 cm
Hence option A is correct.


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