Question

An object is placed perpendicular to the principal axis of a convex lens of a focal length 20cm .the distance of the object from lens is 30cm .find a)the position b) the magnification c) the nature of image formed

Answer 1

 = -30 cm
f = 20 cm, v = ?
Using the lens formula 1/f = 1/v-1/u
We have 1/v = 1/u + 1/f = 1/-30 + 1/20 = -2+3/60 = 1/60

===> 1/v = 1/60
Therefore v = 60cm
Magnification v/u = 60/-30 = -2

Magnification = Image size/Object size

$h _{ i }$/$h _{ o }$ = -2
$h _{ i }$/5 = -2
$h _{ i }$ = -2x5 = -10 cm
The image is real inverted and magnified.

Answer 2

Aloha!

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we are given a convex lens which means:
☆ F= 20 cm ( should be positive )
☆ u= -30 cm. ( is always negative )

to find:
○ v= ?
○ m= ?
○ nature of image formed.

so we the lens formula:

1/F = 1/v - 1/u
1/20 = 1/v - [ 1/-30 ]
1/20 = 1/v + 1/30
1/20 - 1/30 = 1/v
1/v = (3 - 2) / 60. ( taking LCM )
1/v = 1/60
v= 60 cm

now, we know that m= v/u
putting their values we get,

m = 60/-30
m = -2

now, the nature of image:
☆ the image is real and inverted
☆ it is smaller than actual size of object.
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hope it helps
:^)