Question

When two lenses of focal length +5 cm and −25 cm are placed in contact, then the net power of the combination is _______________.

Answer 1

Answer:

here

Explanation:

+5-25/2

-20/2

-10D

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Answer 2

Answer: 16 D

Explanation:

Focal length of the first lens = f₁ = + 5 cm = + 5/100 m

Focal length of the second lens = f₂ = -25 cm = -25/100 m

∴ Net power of the combination

= Power of (the first lens + the second lens)

= P₁ + P₂

= 1/f₁ + 1/f₂

= (100/5 - 100/25)

= (500 -100)/ 25

= 400/25

= 16 Dioptres

= 16 D

Hope you got that.

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