The figure below shows two converging lenses placed L 1 = 19 cmapart. Their foca
ID: 1874551 • Letter: T
Question
The figure below shows two converging lenses placed L1 = 19 cmapart. Their focal lengths are f1 = 10 cmand f2 = 19 cm.
(a)
Where is the final image located for an object that is
L2 = 25 cm
in front of the first lens? (Measure this distance (in cm) relative to the lens of focal length f2.)
distance--------- mdirection ---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.
---------
2Explanation / Answer
a)
let u1 and v1 are the object and image distance fro the first lens.
u1 = 25 cm
f1 = 10 cm
use, 1/u1 + 1/v1 = 1/f1
1/v1 = 1/f1 - 1/u1
1/v1 = 1/10 - 1/25
v1 = 16.7 cm
object distance for the second lens, u2 = 19 - 16.7
= 2.3 cm
f2 = 19 cm
let v2 is the image distance ffor the second lens.
now use, 1/u2 + 1/v2 = 1/f2
1/v2 = 1/f2 - 1/u2
1/v2 = 1/19 - 1/2.3
v2 = -2.62 cm
so, final image distance from second lens is 2.62 cm
direction : to the left of the lens.
b) m1 = -v1/u1
= -16.7/25
= -0.668
m2 = -v2/u2
= -(-2.62)/2.3
= 1.14
overall magnification, M = m1*m2
= -0.668*1.14
= -0.761