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.
Lokesh said:
1 decade ago
Convex is magnifying glass, makes image larger. So its behavior is making big +ve. Concave is indicated as -ve.
Now three lenses are combined to make single lens. To get the property of new lens we have to find out its focal length, it can be calculated by 1/f = 1/f1+1/f2+1/f3.
f1 = f2 = 60, f3 = 15. You will get f = 30.
Now three lenses are combined to make single lens. To get the property of new lens we have to find out its focal length, it can be calculated by 1/f = 1/f1+1/f2+1/f3.
f1 = f2 = 60, f3 = 15. You will get f = 30.
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)
Siddh said:
9 years ago
Two concave lens = 60cm and convex lens = 15cm,
then 1/f = -1/f1 - 1/f2 + 1/f3
= -1/60 - 1/60 + 1/15
= -1/60 - 1/60 + 4/60
= 4 - 2/60
= 2/60
= 1/30.
So, the combination is 30 cm.
then 1/f = -1/f1 - 1/f2 + 1/f3
= -1/60 - 1/60 + 1/15
= -1/60 - 1/60 + 4/60
= 4 - 2/60
= 2/60
= 1/30.
So, the combination is 30 cm.
Suresh Awasthi said:
1 decade ago
Formula: 1/f = 1/f1 + 1/f2.
According to the problem 60 cm on the either side i.e. f1 = f2 = 60 & focal length combination f = ?
Now, 1/f = 1/f1 + 1/f2.
1/f = 1/60 + 1/60.
= 1/30. So combination is 30.
According to the problem 60 cm on the either side i.e. f1 = f2 = 60 & focal length combination f = ?
Now, 1/f = 1/f1 + 1/f2.
1/f = 1/60 + 1/60.
= 1/30. So combination is 30.
AKSHAY GUPTA said:
8 years ago
Formula: 1/f = 1/f1 + 1/f2.
According to the problem 60 cm on the either side i.e. f1 = f2 = 60 & focal length combination f = ?
Now, 1/f = 1/f1 + 1/f2.
1/f = 1/60 + 1/60.
= 1/30. So combination is 30.
According to the problem 60 cm on the either side i.e. f1 = f2 = 60 & focal length combination f = ?
Now, 1/f = 1/f1 + 1/f2.
1/f = 1/60 + 1/60.
= 1/30. So combination is 30.
Katakamsaketh said:
9 years ago
We know that the focal length of the concave lens is negative and convex lens is positive then the focal length of the combination can be found out by using lens formula.
Pankaj yadav said:
8 years ago
1/f = 1/60+1/60,
1/f = 1/30.
The combination of concave f = 30
add with convex,
1/f = 1/30+1/15,
1/f =1/10,
f = 10 cm of combination.
1/f = 1/30.
The combination of concave f = 30
add with convex,
1/f = 1/30+1/15,
1/f =1/10,
f = 10 cm of combination.
Sameer kashmiri said:
9 years ago
1/f =- (1/f1) - (1/f2) + (1/f3).
1/f =- (1/60) - (1/60) + (1/15).
1/f =- (1/30) + (1/15).
1/f = 15/450.
1/f = 1/30.
So, f = 30.
1/f =- (1/60) - (1/60) + (1/15).
1/f =- (1/30) + (1/15).
1/f = 15/450.
1/f = 1/30.
So, f = 30.
Rinku singh said:
8 years ago
f1=f2=-60.
1/F1= 1/-60 +1/-60 =1/-30,
F1 =-30 and given F2 = 15,
1/F = 1/-30 +1/15 =1/30,
F =30 ans.
1/F1= 1/-60 +1/-60 =1/-30,
F1 =-30 and given F2 = 15,
1/F = 1/-30 +1/15 =1/30,
F =30 ans.
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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