Transcript Document

Myanmar
Introduction
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Objectives:

Able to identify regular and diffuse reflection
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Able to explain the laws of reflection
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Able to construct the devices that use the
concepts of reflection of light
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Target group: Secondary level (Grade-7)
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Duration/Mode: 2 periods (1hour 30 mins)
/student-centred
Reflection of Light
Why can’t we see objects in the dark?
Because there is no light.
Light falls on the object.
Light is sent back
from the object and
enters the eyes.
We can see objects only when there is light.
Content
Section-A
- Reflection of Light
Section-B
-Formation of image in
a plane mirror
Section-C
Quit
- Periscope,
Quit
Kaleidoscope
Section-A
Reflection of light
When light is incident on the surface of an
object some of the light is sent back and
this phenomenon is called reflection of
light.
Click on each item to study more.
Contents
Types
Terms
Laws
Section-A
Reflection
Regular
Reflection
Diffuse
Reflection
Click on each item to study more.
Section-A
Regular
Reflection
smooth surfaces
When a parallel beam of
light is incident on a plane
mirror, the angles of
incidence of all the rays are
equal. Thus all the rays are
reflected in one direction.
Such reflection of light is
called regular reflection.
Section-A
Diffuse
Reflection
rough surfaces
When a parallel beam of
light is incident on a rough
surface, the rays are
reflected
in
different
directions. Such reflection of
light is called diffuse
reflection.
Terms on reflection of light
Section-A
normal
angle of incidence
A
incident ray
M
N
angle of reflection
i r
O
Click on each item to study more.
B
reflected ray
M'
Section-A
An incident ray
AO
• A ray which represents the incident light is an
incident ray.
A
M
M'
O
Section-A
A reflected ray
OB
• A ray which represents the reflected light is a
reflected ray.
A
M
N
O
B
M'
Section-A
A normal
ON
• A line perpendicular to the surface at the point of
incidence is called a normal.
A
M
N
O
M'
Section-A
An angle of incidence
i
• An angle between the incident ray and the normal is
an angle of incidence.
N
A
i
M
O
M'
Section-A
An angle of reflection
r
• An angle between the reflected ray and the normal is
an angle of reflection.
A
N
B
i r
M
O
M'
Section-A
Laws of Reflection
1. The incident ray, the reflected ray
and the normal all lie in the same
plane.
2. The angle of incidence is equal to
the angle of reflection.
Exercise-1
Section-B
Formation of image in a plane mirror
Stand in front of a looking glass and look at your image.
1. Can you receive your image on a screen ?
2. Is the image erect or inverted?
3. Is the image the same size or larger or smaller?
4. What happens when you tilt your head to the right?
5. How does the image move when you step forward or
backward
6. Where is the image formed ?
Section-B
Formation of image in a plane mirror
The properties of the image formed in a plane mirror
are as follows:1.
The image is virtual.
2.
The image is erect.
3.
The image is of the same size as the object.
4.
The image is laterally inverted.
5.
The image is as far behind the mirror as the
object is in front.
6.
The image is situated on the line passing
through the object and perpendicular to the
plane mirror.
Exercise-2
Section-C
Instructions:
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


Divide the class into six groups.
Group A, B and C have to make a periscope.
Group D, E and F have to make a kaleidoscope.
Follow the instructions given in the websites.
Section-C
Click on the "Periscope" to view the web site.
Let’s make a
periscope.
Periscope
A periscope is an optical
instrument that lets you see
around corners and over
walls.
Click here to view the web page and make
a periscope.
Section-C
Click on the "Kaleidoscope" to view the web site.
Kaleidoscope
let’s make a
kaleidoscope.
A kaleidoscope is a tube
containing mirrors and
small pieces of coloured
paper cut into tiny shapes.
It uses reflections to make
colourful patterns.
Click here to view the web page and make
a kaleidoscope.
Quit
You are about to end this lesson.
Are you sure?


Click Yes to exit.
Click No to return to the content slide.
Yes
No
Credit
Created by –
Daw Khin Khin Thein and
Science Group, B.E.H.S (2) Dagon, Union of Myanmar
Web References–
http://www.exploratorium.edu/science_explorer/periscope.html
http://www.town4kids.com/town4kids/kids/science/explore/kalei.htm
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