Test Index

CBSE Class 12 Physics 2020 Delhi Set 1 Paper

© examsnet.com
Question : 32
Total: 37
An optical instrument uses a lens of power 100D for objective lens and 50D for its eyepiece. When the tube length is kept at 25‌cm, the final image is formed at infinity.
(a) Identify the optical instrument.
(b) Calculate the magnification produced by the instrument.
Solution:  
(a) The instrument is called compound microscope.
(b) Power of objective =PO=100D
∴‌fO=‌
1
100
m=1‌cm
∴‌‌ Power of eyepiece ‌=PE=50D
∴‌fE=‌
1
50
m=2‌cm
Length of tube =L=25‌cm
D= least distance of distinct vision =25‌cm
Magnification =‌
L
fO
×‌
D
fE

∴‌‌ Magnification =‌
25
1
×‌
25
2
=312.5
© examsnet.com
Go to Question:
Prev Question
Next Question