A lens forms the image of an object placed at a distance of 45 cm from it on a screen placed at a distance 90 cm on other side of it. (a) Name the kind of lens. (b) Find : (i) the focal length of lens, and (ii) the magnification of image.
[ 2 Marks]

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Solution

(a)
As the image is formed on the other side of the lens the image is real .Hence the lens is a convex lens
[ 0.5 Marks]
(b)
(i)Lens formula is
1/f=1/v-1/u
1/f=1/90-1/-45
1/f=3/90
f=30 cm
[ 1 Marks]
(ii)
For a lens , magnification is
m=v/u
m=90/-45
m=-2
[ 0.5 Marks]

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A lens forms the image of an object placed at a distance of 45 cm from it on a screen placed at a distance 90 cm on other side of it. (a) Name the kind of lens. (b) Find : (i) the focal length of lens, and (ii) the magnification of image. [ 2 Marks]

(a) As the image is formed on the other side of the lens the image is real .Hence the lens is a convex lens [ 0.5 Marks] (b) (i)Lens formula is 1/f=1/v-1/u 1/f=1/90-1/-45 1/f=3/90 f=30 cm [ 1 Marks] (ii) For a lens , magnification is m=v/u m=90/-45 m=-2 [ 0.5 Marks]

A lens forms the image of an object placed at a distance of 45 cm from it on a screen placed at a distance 90 cm on other side of it. (a) Name the kind of lens. (b) Find : (i) the focal length of lens, and (ii) the magnification of image.
[ 2 Marks]

(a)
As the image is formed on the other side of the lens the image is real .Hence the lens is a convex lens
[ 0.5 Marks]
(b)
(i)Lens formula is
1/f=1/v-1/u
1/f=1/90-1/-45
1/f=3/90
f=30 cm
[ 1 Marks]
(ii)
For a lens , magnification is
m=v/u
m=90/-45
m=-2
[ 0.5 Marks]