Question

Two lenses in contact: Find the equivalent power, the image location, and magnification

f₁ = 5 cm f₂ = -10cm d₁₂ = 0 p₁ = 20 cm

Answer: P = +10 D; q = +20 cm; m= -1

I need to know how to solve this problem

Answer 1

let f is resultant focal length.

we know, when two lenses are in contact

1/f = 1/f1 + 1/f2 +

1/f = 1/5 + 1/(-10)

f = 10 cm = 0.1 m

Power of the resultant lenses, P = 1/f

= 1/0.1

= 10 D <<<<<<----------------Answer

let object distance p = 20 cm

let q is the image distance.

use, 1/p + 1/q = 1/f

1/q = 1/f - 1/p

1/q = 1/10 - 1/20

q = 20 cm <<<<<<----------------Answer

magnification, m = -p/q

= -20/20

= -1 <<<<<----------------Answer