Answer to Question #182797 in Optics for Kenan

Question

An object 4 cm high is placed 30 cm in front of the condenser lens. The focal length of this lens is 10 cm. a) Determine the position, height and orientation of the image. b) Suppose that you only now place a second, also converging lens to the right of the first lens at a distance of 20 cm from the first. Determine the focal length of the second lens if the image given by this two-lens system is formed 13.3 cm to the right of the first lens. The mentioned final image is inverted in relation to the original object. (Answer: a) di = 15 cm, m = -0.5, hi = -2 cm b) f₂ = 19.7 cm) I solved for a) but I don't know how to do under b).

Answer 1

given:

h_o=4

u= -30 cm

f₁=10 cm

a) using lens formula

$\boxed{{1\over v}-{1\over u}={1\over f}}$

we get,

v₁=15 cm from the first lens....

(b)

now ,

$\bigstar$ for second lens,image from first lens will behave as an object

so,

u₂= -5 cm

and given that final image is formed 13.3 cm right of 1st lens means 6.7 from second lens.

therefore,

v₂= -6.7 cm

therefor using lens formula for second lens,

$\boxed{{1\over v}-{1\over u}={1\over f}}$

$\boxed{{1\over (-6.5)}-{1\over( -5)} ={1\over f}}$

${1\over f}=0.0461$

$\boxed {f_2=21.69}$ this is right answer for f₂ .