Question

# 1) Two convex lenses, both with focal length 1.5 m, are placed such that the light...

1) Two convex lenses, both with focal length 1.5 m, are placed such that the light from a 4 cm tall object passes through each. The object is placed 4.5 m from the first lens, and the lenses are 3 m apart. Where will the image from the first lens be? Will it be real or virtual? Will it be upright or inverted? Where will the final image be (using both lenses)? Will it be real or virtual? Upright or inverted? What will the height of the final image be?

2) A glass lens with index of refraction 1.52 is ground such that the front of the lens is convex with radius 1.6 m, and the back of the lens is concave with radius 2.1 m. What is the refractive power of the lens? What is the focal length of the lens?

#### Homework Answers

Answer #1

1.

using lens formula for 1st lens

1/f = 1/v - 1/u

1/1.5 = 1/ v + 1/4.5

v = 2.25 m ==>> Ans

image is real, inverted

now the above acts as object for lens2

object distance of which is given by

u' = 3 - 2.25 = 0.75 cm

using lens formula again

1/1.5 = 1/v' + 1/0.75

v' = 1.5 m ==>> Ans

image is virtual

image height is given by

h' = h ( v'/u') (v/u)

h' = 4* (1.5 / 0.75)* ( 2.25 / 4.5)

h' = 4 cm

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plz post other problem separately

Comment before rate in case any doubt, will reply for sure.. goodluck

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