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Refraction. pptx refraction of light
1. Refraction of Light in Lenses
“Refraction is the change in the direction of a wave
passing from one medium to another.”
The bending is caused due to the differences in density
between the two substances.
Lens is a transparent material made of glass or
plastic that refracts light rays and focuses (or appear to
focus) them at a point.
2. Why do stars twinkle?
Did you know that the twinkling
effect of stars is due to
atmospheric refraction?
The starlight undergoes
several refractions while reaching
the Earth. This atmospheric
refraction occurs in a medium of
gradually changing refractive
index.
3. Causes of Refraction
Change of Speed Results in Change in Direction
A light ray refracts whenever it travels at an angle into a
medium of different refractive indices.
This change in speed results in a change in
direction. As an example, consider air travelling into
water.
The speed of light decreases as it continues to
travel at a different angle.
4. The refraction of light in
glass is shown in the figure above.
When light travels from air into
glass, the light slows down and
changes direction slightly.
When light travels from a
less dense substance to a denser
substance, the refracted light
bends more towards the normal
line. If the light wave approaches
the boundary in a perpendicular
direction, the light ray doesn’t
refract despite the change in
speed.
5.
6. 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.
7. 2. Convex 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.
8. Images Formed by Lenses
In locating the image formed in lenses graphically, two
important points are considered. The following important points are
enumerated below.
9. 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.
10.
11.
12.
13. To graphically determine the position and kind of the image
formed, the ray diagram can be used. Consider the following steps
using the three major rays described above:
1. From the object, draw the first ray (P–F ray). From the same
point on the object, draw the second (F–P ray), and third (V
ray) rays.
2. The intersection of the rays is the image point corresponding to
the object point. For example, if you started diagramming from the
tip of the arrow-shaped object, the intersection of the refracted
rays is also the tip of the arrow-shaped image. Thus, you can
determine completely the position and characteristics of the image.
14. 3. For a concave lens, light rays diverge from a virtual focus; but
the procedure for locating images is the same as for convex lenses.
Activity 8
Are you L-O-S-T after Refraction?
Objectives:
• Construct ray diagrams for lenses.
• Determine graphically the location, orientation, size, and type of
image formed.
• Show graphically the changes in the image formed as an object’s
position is changed.
15.
16.
17.
18.
19.
20.
21. Q1. Refer to Table 9. How does the image change in its size and
location, as the object comes nearer the convex lens? Concave
lens?
Q2. Refer to the size of object and the size of image from the
drawn ray diagrams for convex lens. Identify the location of object
for which the following optical instruments are used to.
22. Q3. Why is it impossible for a concave lens to form a real image?
