Question

The figure below shows two converging lenses placed L₁ = 23 cm apart. Their focal lengths are f₁ = 10 cm and f₂ = 25 cm.

(a)

Where is the final image located for an object that is L₂ = 32 cm in front of the first lens? (Measure this distance (in cm) relative to the lens of focal length f₂.)distance cmdirection ---Select--- to the left of the lens to the right of the lens

(b)

What is the total magnification of the lens system? Note: Do not calculate a total angular magnification in this case since we are not dealing with a microscope.

Answer 1

given :

f1 = +10 cm

f2 = +25cm

separation between the lenses = 23 cm

u1 = object distance for lens 1 = -32cm

v1 = image distance for lens 1 = ?

u2 = object distance for lens 2 = ?

v2 = image distance for lens 2 = ?

a) Using lens equation for lens 1 :

[ v = image distance, u = object distance, f = focal length]

=> v1 = 160/11 cm

u1 = object distance for lens 2 = (23 - 160/11) = -93/11 cm

now, using lens equation for lens 2 :

=> v2 = -2325/182 =-12.77 cm.

Therefore, the final image is formed at a distance 12.77cm from the second lens and to the left of 2nd lens. [answer]

b) Total magnification = M = magnification by lens 1 * magnification by lens 2

  [answer]