What is equivalent lens ? obtain an expression for the equivalent focal length of two thin lenses separated
by a distance d.
Answers
Answer:
Explanation:
Let the focal lengths of the two lenses be f
1
and f
2
.
u
1
=OC
1
and
v
1
=I
1
C
1
u
2
=−C
1
I
1
which is approximately equal to C
2
I
1
and
v
2
=C
2
I which is approximately equal to C
1
I
∴
u
1
1
+
v
1
1
=
f
1
1
and
u
2
1
+
v
2
1
=
f
2
1
OC
1
1
+
I
1
C
1
1
=
f1
1
and
−C
1
I
1
1
+
C
1
I
1
=
f
2
1
So
OC
1
1
+
I
1
C
1
1
=
f
1
1
+
f
2
1
=
F
1
.
Combined focal length of two thin lenses in contact is given by:
F=
f
1
+f
2
f
1
f
2