Question

find the focal length of combination lens formed by placing in contact two thin of lenses of power +2.5d and -2d​

Answer 1

Answer:

Focal length= 2m

Explanation:

Power of combination= P1 +P2

= 2.5 + (-2)

Pcomb= 0.5 D

f comb= 1/Pcomb

=1/0.5

=2m

Answer 2

Answer:

2m

Explanation:

$\frac{1}{f} = p \\ and \: in \: combination \: new \: focal \: length \\ \frac{1}{f} = \frac{1}{f1} + \frac{1}{f2} ..... \\ \frac{1}{f} = 2.5 + ( - 2) \\ \frac{1}{f} = 0.5 \\ f = 2$