Myanmar

Introduction Objectives:

Able to identify regular and diffuse reflection

Able to explain the laws of reflection

Able to construct the devices that use the

concepts of reflection of light

Target group: Secondary level (Grade-7)

Duration/Mode: 2 periods (1hour 30 mins)

/student-centred

Reflection of Light

We can see objects only when there is light.

Why can’t we see objects in the dark?

Light is sent back from the object and enters the eyes.

Light falls on the object. Because there is no light.

Section-A

Section-C

Section-B

ContentContent

- Reflection of Light

- Formation of image in a plane mirror

Kaleidoscope- Periscope,

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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.

Section-A

Click on each item to study more.

Types Terms LawsContents

Regular ReflectionRegular

Reflection

ReflectionReflection

Diffuse ReflectionDiffuse

Reflection

Click on each item to study more.

Section-A

Regular ReflectionRegular

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 ReflectionDiffuse

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.

Section-A

i r

A

O

NB

M M'

angle of incidence angle of reflection

incident ray reflected ray

normal

Terms on reflection of light

Click on each item to study more.

Section-A

• A ray which represents the incident light is an incident ray.

An incident ray

A

OM M'

AOSection-A

• A ray which represents the reflected light is a reflected ray.

A reflected ray OB

A

OM M'

NB

Section-A

• A line perpendicular to the surface at the point of incidence is called a normal.

A normal

A

OM M'

ON

N

Section-A

• An angle between the incident ray and the normal is an angle of incidence.

An angle of incidence i

A

OM M'

N

i

Section-A

• An angle between the reflected ray and the normal is an angle of reflection.

An angle of reflection r

NA

OM M'

i

B

r

Section-A

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.

Laws of Reflection

Exercise-1

Section-A

Formation of image in a plane mirrorFormation of image in a plane mirror

Stand in front of a looking glass and look at your image.

2. Is the image erect or inverted?

Section-B

1. Can you receive your image on a screen ?

3. Is the image the same size or larger or smaller?

6. Where is the image formed ?

4. What happens when you tilt your head to the right?

5. How does the image move when you step forward or backward

Formation of image in a plane mirrorFormation 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.

Section-B

Exercise-2

Instructions:

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 here to view the web page and make a periscope.

Periscope

Let’s make a periscope.

A periscope is an optical instrument that lets you see around corners and over walls.

Section-C

Click on the "Periscope" to view the web site.

Kaleidoscopelet’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.

Section-C

Click on the "Kaleidoscope" to view the web site.

You are about to end this lesson.Are you sure?

Click Yes to exit. Click No to return to the content slide.

Yes No

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Credit

Created by – Daw Khin Khin Thein andScience Group, B.E.H.S (2) Dagon, Union of Myanmar

Web References–

Created by – Daw Khin Khin Thein andScience Group, B.E.H.S (2) Dagon, Union of Myanmar

Web References–

Quit

http://www.exploratorium.edu/science_explorer/periscope.html

http://www.town4kids.com/town4kids/kids/science/explore/kalei.htm