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 1 of 4.
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)
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)
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)
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)
Julia roberts said:
8 years ago
1/f=1/f1+1/f2.
concave=-ve.
convex=+ve.
1/f=1/15-(1/60+1/60).
.: f=30.
concave=-ve.
convex=+ve.
1/f=1/15-(1/60+1/60).
.: f=30.
(1)
Vamsi said:
8 years ago
Explain this sum cleary.
(1)
Akash said:
8 years ago
1/f = 1/f1+1/f2.
1/f = 1/60+1/60.
1/f = 1/30 answer.
1/f = 1/60+1/60.
1/f = 1/30 answer.
(1)
Rashmi said:
7 years ago
Please explain me the answer.
(1)
Ravi said:
1 decade ago
1/f = 1/f1+1/f2.
1/60 = 1/15+1/f2.
1/60-1/15 = 1/f2.
1/f2 = 1/30.
f2 = 30.
1/60 = 1/15+1/f2.
1/60-1/15 = 1/f2.
1/f2 = 1/30.
f2 = 30.
(1)
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.
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