Statement 1 : If P₁ and P₂ be the powers of two thin lenses
located coaxially in a medium of refractive index μ at a
distance d, then the power P of the combination is
P = P₁ + P₂ – P₁P₂d/μ
Statement 2 : Because for above given system equivalent
focal length is given by F = f₁f₂/f₁+f₂-d/μ and P = 1/F
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Answer:
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Explanation:
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12th
Physics
Ray Optics and Optical Instruments
Combination of Lenses
When two thin lenses of foc...
PHYSICS
When two thin lenses of focal lengths f
1
and f
2
are kept coaxially and in contact, prove that their combined focal length "f" is given by
f
1
=
f
1
1
+
f
2
1
October 15, 2019
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Naseha Keluth
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VIDEO EXPLANATION
ANSWER
Let a point object O is placed on the principal axis
By lens formula for image formation by lens L
1
v
′
1
−
u
1
=
f
1
1
....... (1)
I' serves as a virtual object for the second lens L
2
which forms a final image I at a distance 'v'. Then for L
2
v
1
−
v
′
1
=
f
2
1
........ (2)
Adding equation (1) and (2)
v
1
−
u
1
=
f
1
1
+
f
2
1
.......... (3)
If we replace these two lenses by a single lens such that if an object is kept at u image is formed at v then its focal length f is given by
v
1
−
u
1
=
f
1
....... (4)
From equation (3) and (4) we get
f
1
=
f
1
1
+
f
2
1
Answer:
Detailed answer is attached below
Explanation: