Civil Engineering - Surveying - Discussion
Discussion Forum : Surveying - Section 1 (Q.No. 22)
22.
Two concave lenses of 60 cm focal length are cemented on either side of a convex lens of 15 cm focal length. The focal length of the combination is
Discussion:
38 comments Page 4 of 4.
Hariom said:
7 years ago
Yes. It is 30.
Sammy said:
7 years ago
Simple.
1/f = -1/f -1/f + 1/f.
1/ f= -1/60 -1/60 + 1/15.
1/f= -1/30 + 1/15.
1/f= 1/30.
F=30.
1/f = -1/f -1/f + 1/f.
1/ f= -1/60 -1/60 + 1/15.
1/f= -1/30 + 1/15.
1/f= 1/30.
F=30.
Rashmi said:
7 years ago
Please explain me the answer.
(1)
TSKD said:
7 years ago
Since two cancave is sandwitched with one convex ie.,
1/f = 1/60 + 1/60 - 1/15,
1/f = 1/30.
1/f = 1/60 + 1/60 - 1/15,
1/f = 1/30.
(6)
Dev Kumavat said:
6 years ago
Thank you @Sameer Kashmiri.
NAVEEN said:
5 years ago
1/f = 1/F1+1/F2.
1/60 = 1/15+1/F2.
F = 30.
1/60 = 1/15+1/F2.
F = 30.
(7)
Poj said:
4 years ago
Concave (-) and convex (+).
Given:
Two concave i.e F1 = -1/60.
F2 = -1/60.
One convex lens i.e F3 = 1/15.
combined focal length = (F1 + F2) + F3.
= { ( -1/60) + ( -1/60) } + 1/15,
= (-2/60) + 1/15,
= -1/30 + 1/15,
= -1+2/30,
= 1/30 = 30.
Given:
Two concave i.e F1 = -1/60.
F2 = -1/60.
One convex lens i.e F3 = 1/15.
combined focal length = (F1 + F2) + F3.
= { ( -1/60) + ( -1/60) } + 1/15,
= (-2/60) + 1/15,
= -1/30 + 1/15,
= -1+2/30,
= 1/30 = 30.
(27)
Neeraj Kumar singh said:
4 years ago
1/f = 1/15 - 1/60 - 1/60.
1/f = 1/30,
F = 30.
1/f = 1/30,
F = 30.
(5)
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