Question

Two lenses of power +3.5D and -1.5D are placed in contact what is the power and the focal length of the combination? If an object be placed at a distance of 0.8m from the lens combination, where is the image formed?

Answer 1

Power of the combination = P1 +P2
P = 3.5 - 1.5 = 2 D.
P =1/f
f = 1/P = 1/2 = 0.5 m.
u = 0.8 m.
Apply lens formula
1/f = 1/v - 1/-u
1/v = 1/f - 1/u
V = uf/u - f
v = 0.8 × 0.5/0.8-0.5

Hence v = 1.33 m.
Image formed at a distance of 1.33 m from the lens
Hope this helps...

Answer 2

Power of the combination = P1 +P2

P = 3.5 - 1.5 = 2 D.

P =1/f

f = 1/P = 1/2 = 0.5 m.

u = 0.8 m.

Apply lens formula

1/f = 1/v - 1/-u

1/v = 1/f - 1/u

V = uf/u - f

v = 0.8 × 0.5/0.8-0.5

Hence v = 1.33 m.

Image formed at a distance of 1.33 m from the lens

Pls mark me brainliest!