The document discusses the basic principles of lenses, highlighting the differences between convex and concave lenses, including their characteristics and the types of images they form. It explains how lenses refract light to create real and virtual images and provides instructions for constructing ray diagrams to analyze these images. The lesson aims to help learners understand the functionality of lenses and the qualitative characteristics of the images they produce.

1. Lord, true source of light
and wisdom, give me keen
sense of understanding, a
retentive memory and a
capacity to grasp things
correctly.

2. Grant me the grace to
be accurate in my
expositions and the skill
to express myself with
thoroughness and clarity.

3. Be with me at the start of
my work, guide its
progress and bring it to
completion.
Grant, this through Christ,
our Lord. Amen

4. Good morning 
GOOD AFTERNOON 

5. Even if we failed
yesterday, we can try
again today.
-Anonymous

6. In this lesson, learners will able you to :
• Describe the two types of lenses.
• Explain how images are formed in
different types of lenses.
• Perform ray diagramming in lenses.
Objectives:

7. In the previous lesson, you explored about the
qualitative characteristics of images formed by
mirrors both plane and curved mirrors. In this
module, you now learn about basic
information about lenses and how they work.
Just like in mirrors, you will also explore the
qualitative characteristics of images formed by
lenses.
Introduction:

8. Well the most apparent distinction between
mirrors and lenses are: mirrors reflect light
rays (light bounces back) while light rays
are refracted (pass-through) through a
lens. A mirror has only one focal point. A
lens has two focal points each on either
side.

10. Refraction of Light in Lenses
You learned in Grade 8 that Refraction is the
bending of light when it travels from one medium to
another of different optical densities. The ancient
Greeks used the concept of light refraction in their
living like using a lens to focus light rays. A lens is a
transparent material made of glass or plastic that
refracts light rays and focuses (or appear to focus)
them at a point.
Development:

11. A lens works by refraction of light. Light rays
bend as they pass through the lens resulting to
a change in direction. This means the rays
seem to come from a point that's closer or
further away from where they actually originate
and that's what makes objects seen through a
lens seem either bigger or smaller than they
really are.

13. Lenses are made of transparent substance like
glass or plastic which can bend light rays. Lenses
are of two kinds: Types of Lenses
1. Convex Lens
It is thicker in the center than edges. It forms real
images and virtual images depending on position of
the object. It is also called Converging Lens
because the light that passes through it tends to
converge at a particular point called the focal point.

14. 2. Concave Lens
It is thicker at the edges and thinner in
the center. It forms upright and reduced
images. It is also called Diverging Lens
because the light that passes through it
tends to diverge at a particular point
called the focal point.

17. Characteristics of Optical Images
Formed in Lenses
Lenses, just like curved mirrors can form images
that are real or virtual. Real images formed by
lenses are inverted images that can be seen by
projecting it on a screen. While virtual images are
upright images that are seen directly. Spherical
lenses usually have two centers of curvature
which are the centers of the intersecting spheres
which form the lens surfaces.

18. In lenses, the focus is not midway between
the lens and the center of curvature as we
found to be in spherical mirrors. Its position on
the principal axis depends on the index of
refraction of the lens. With a double convex
lens of crown glass, the principal focus almost
coincides with the centers of curvature, thus
the radius of curvature and the focal length
are almost equal.

20. The ‘Three Most Useful Rays’ in Lenses
Images formed in a lens can be
located and described through ray
diagramming. The following three most
useful rays for convex and concave
lenses are presented below.

24. Learning Task 2: Construct ray diagrams to
locate and describe the image formed by
a thin lens at different positions of the
object from the lens. Use red ink for ray 1,
black ink for ray 2, and blue ink for the
image. Describe the image formed in terms
of LOST, L for location, O for orientation, S
for size, and T for type.