two plano convex lenses of focal length 10 cm and 20 cm are placed in contact with each other . effective focal length of the image formed by the lens is
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Answer:
Correct option is
C
+5D
Power of the concave lens =
f
1
=
−20
100
D=−5D
Power of the convex lens =
f
1
=
10
100
D=+10D
Thus, the power of the combination =P
1
+P
2
=+10D−5D=+5D
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