A lens is used as a magnifier to view an ant placed on a piece of paper. The ima

Question

A lens is used as a magnifier to view an ant  placed on a piece of paper. The image of the ant is 15cm from the lens and the magnification factor is 3.

a) How far from the paper (the ant) is the lens?

b) What is the focal length of the lens? Is it converging or diverging?

c) Is the image virtual or is it real?

d) Suppose you now use a new lens whose  focal length is 10cm to read a news paper, but your near point is 30cm. how far should the lens be from the paper.

c) Now suppose you use this lens as part of a cameral, and you want to photograph an objject which is 50am to the left of the camera. What is the distance between the lens and the film.

In each case  draw a diagram showing how image is located using at least two principle rays. (You may represent the object as a vertical arrow each time) i.e. one diagram for (a,b,c) another for (d) and third for (e). Please explain your answers.

Explanation / Answer

given, v = 15 cm (image distance)
a)
m = v/u

3 = v/u

u = v/3

= 15/3

= 5 cm (object distance)
b)
1/f = 1/u + 1/v

= 1/5 + 1/15

f = 3.75 cm

c) real

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