Page 50 - Physics 10_Float

GEOMETRICAL OPTICS

parallel to the principal axis after refraction by the
lens. For your information
Ray 1 You can compare lenses simply
Ray 1
Ray 2 by looking at them.
F F A lens with a long focal length
Object is thin; its surfaces are not very
Ray 3 strongly curved.
Ray 3 Real
A lens with a short focal length
image
is fatter; its surfaces are more
f f strongly curved.
Fig. 12.23: Convex Lens

The ray diagram for concave lens is shown in Fig.12.24.

Ray 1
Ray 1
Physics insight
Ray 3

Object F Virtual F
image Ray 2

A converging lens becomes a
f f magnifying glass when an object
is located inside the lens's focal
Fig. 12.24: Concave Lens
length.
Image Formation in Convex Lens
In class VIII, we have learnt image formation by lenses. Let us
briefly revise image formation by convex lens (Fig.12.25).
(a) Object beyond 2F Physics insight

Object F 2F
2F F Image F
F

The image is between F and 2F, real, inverted, smaller than the object.
(b) Object at 2F A diverging lens always has the
same ray diagram, which forms
Object F 2F a smaller image.
2F F Image

The image is at 2F, real, inverted, the same size as the object.
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