Page 199 - Physics_Form_2

Refraction and dispersion of light

and the whiteness of clouds these prisms act together, they produce a bright
reveal about the behavior of image focused at a point as shown in Figure 5.30.
light? Converging lens Diverging lens

4. Explain why an object which
appears yellow in daylight,
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appears red when illuminated
with a red light and black when
illuminated with a blue light?
5. What is the difference between
secondary and complementary
colours in light?
6. Explain the appearance of a Figure 5.30: A set of prisms packed to converge or
red tie with blue spots when diverge light rays
observed in
(a) red light. Convex and concave lenses
(b) green light. Lenses differ from one another in terms of their
7. Briefly describe two methods shape and the materials from which they are
of combining spectrum colours made. Based on their shapes, there are two
to produce white light. major types of lenses. These are the convex
(converging) lenses and concave (diverging)
Refraction of light by lenses lenses.

A piece of glass or other transparent A convex lens is a lens that converges rays
material may be shaped in such a of light that pass through it. Convex lenses
way that, parallel incident light are relatively thicker across their middle and
rays passing through it would either thinner at their edges as shown in Figure 5.31.
converge to a point or appear to At least one side of a convex lens curves
diverge from a point. A piece of glass outwards. Convex lenses can be further
that has such a shape is referred to as categorized depending on their specific shapes.
a lens. Though most lenses are made These include bi-convex lenses, plano-convex
of glass, it is possible to make lenses lenses and convex meniscus lenses as depicted
from various transparent materials. in Figure 5.31. Task 5.5 demonstrates the
In recent times, the use of plastic for action of a convex lens.
making lenses has been increasing.
A lens is therefore a carefully molded
piece of transparent material that
refracts light rays in such a way that
an image is formed. Lenses can be
thought of as a series of tiny refracting
prisms, each of which refracts light Biconvex Plano-convex Converging meniscus
to produce their own image. When Figure 5.31: Type of convex lenses

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