Question

the convex lenses of focal length 10cm and 20cm are placed in contact. the effective power of the lens system is?​

Answer 1

15D is the effective power of the combination of the lenses.

Explanation:

Given that,

$f_{1}$ = 10 cm = 0.1 m

$f_{2}$ = 20cm = 0.2 m

As we know,

$P_{1}$ = 1/$f_{1}$

= 1/0.1

= 10D

$P_{2}$ = 1/$f_{2}$

= 1/0.2

= 5D

The Combined power of the lenses (P) = $P_{1}$ + $P_{2}$

= 10D + 5D

= 15D

Learn more: Power of the lenses

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