A convex lens forms an inverted image of size same as that of the object which is placed at a distance 60 cm in front of the lens. Find :
(a) the position of image, and
(b) the focal length of the lens
A convex lens forms an inverted image of size same as that of the object which is placed at a distance 60 cm in front of the lens. Find :
(a) the position of image, and
(b) the focal length of the lens
When an object is placed at the centre of curvature, 2F1, of a convex lens, its image is formed at the centre of curvature, 2F2, on the other side of the lens. The image formed is inverted and of the same size as the object, as shown in the given figure.
It is given that the image of the needle is formed at a distance of 60 cm from the convex
lens. Hence, the needle is placed in front of the lens at a distance of 60 cm.
Object distance, u = −60 cm
Image distance, v = 60 cm
Focal length = f
According to the lens formula,
1/v-1/u=1/f
1/f=1/60-1/(-60)
1/f=1/60+1/60
1/f=2/60=1/30
1/f=1/30
f=30cm=0.30m
power of the lens P
P=1/f(in meters) =1/0.30=+3.33D
hence the power of the given lens is +3.33D
When an object is placed at the centre of curvature, 2F1, of a convex lens, its image is formed at the centre of curvature, 2F2, on the other side of the lens. The image formed is inverted and of the same size as the object, as shown in the given figure.
It is given that the image of the needle is formed at a distance of 60 cm from the convex
lens. Hence, the needle is placed in front of the lens at a distance of 60 cm.
Object distance, u = −60 cm
Image distance, v = 60 cm
Focal length = f
According to the lens formula,
1/v-1/u=1/f
1/f=1/60-1/(-60)
1/f=1/60+1/60
1/f=2/60=1/30
1/f=1/30
f=30cm=0.30m
power of the lens P
P=1/f(in meters) =1/0.30=+3.33D
hence the power of the given lens is +3.33D
