Question

Choose the Correct Answer
1. Two lenses of power + 12D and -2D are placed in contact. The focal length of the combinatie
100
[Hint : P = P, + P, and F= p!
A) 20 cm
B) 5 cm
C) 25 cm
D) 10 cm​

Answer 1

Answer:D

Explanation:-12+2D=10D

D=100/f

f=100/D

f=10

Answer 2

$\underline{ \boxed{ \bold{ \rm{ \purple{ \huge{Answer}}}}}}$

Given :

Two lenses of power +12D and -2D are placed in contact.

To Find :

The focal length of given combination.

Formula :

Power of combination of lenses is given by

$\: \: \: \: \: \: \: \: \: \: \: \: \dag \: \underline{ \boxed{ \bold{ \rm{ \pink{P = P_1 + P_2}}}}} \: \dag$

Relation between power of lens and focal length is given by

$\: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \dag \: \underline{ \boxed{ \bold{ \rm{ \blue{P = \frac{1}{f}}}}}} \: \dag$

Calculation :

$\implies \rm \: P = P_1 + P_2 = 12 - 2 \\ \\ \therefore \rm \: \red{P = 10 \: D} \\ \\ \implies \rm \: f = \frac{1}{P} = \frac{1}{10} = 0.1 \: m \\ \\ \therefore \: \underline{ \boxed{ \bold{ \rm{ \orange{f = 10 \: cm}}}}}$