Question

Two thin lenses of power +3.5 D and -2.5 D are placed in contact,

find the power and focal length of the lens combination.​

Answer 1

Answer:

P = 1 D

f = 1 m = 100 cm

Explanation:

The power of the combination of lenses is simply found out by adding the power of the individual lens:

$P = P_{1}+P_{2}$

where,

P = Power of combination of lenses = ?

P₁ = Power of first lens = 3.5 D

P₂ = Power of second lens = -2.5 D

Therefore,

$P = 3.5\ D - 2.5\ D$

P = 1 D

Now, for focal length:

$Focal\ Length = f = \frac{1}{D}\\\\f = \frac{1}{1\ D}$

f = 1 m = 100 cm