A specific magnifying glass is used to achieve a magnification of -3 when an obj

Question

A specific magnifying glass is used to achieve a magnification of -3 when an object is placed only 5 cm away from it.

a) What is the focal length of the magnifying glass? cm

b) What type of lens is the magnifying glass? plane concave convex unknown

c) The image would be real or virtual ,inverted or upright and enlarged or reduced?

d) It is possible to use this magnifying glass to burn a hole through a piece of paper. If you were to use light rays from the sun to do this, how far away from the paper would you need to hold the magnifying glass?

between the lens and the focal point

at the focal point

between the focal point and the center of curvature

beyond the center of curvature

Explanation / Answer

solution:

use lens formula

1/f =1/do +1/di

M (magnification) =-di/do

M =-3 =-di/do and d0 =5cm

di =15cm

1/f =1/5 +1/15

f =3.75cm ans a

focal length is positive so lens is convex ans b

since M is negative and is =-3 so image would be virtul enarged ans c

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