Question

An object placed 10cm in front of a lens has an image 20cm behind the lens. What is the power of the lens (in dioptre)?

Answer 1

POWER = 1\F

NOW BY LENS FORMULA, AND , V=+20cms AND U = -10cms,

1\F = 1\V - 1\U

1\F = 1\20 + 1\10

1\F = 3\20

F = 20\3 ⇒ 6.67cms.

NOW,

POWER = 1\F

POWER = 1\6.67

POWER = 0.149DIOPTRE.

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