A Lesson Plan in PhysicsA Lesson Plan in Physics

LIGHTLIGHT

Prepared by:

Evelyn S. Lauron

Paknaan National High School

OBJECTIVES:OBJECTIVES:

Describe nature of lightDescribe nature of light Identify and describe transparent, Identify and describe transparent,

translucent and opaque objectstranslucent and opaque objects Differentiate luminous and non Differentiate luminous and non

luminous bodiesluminous bodies Define and describe reflectionDefine and describe reflection

SUBJECT MATTER:SUBJECT MATTER:

LIGHTLIGHT

CONCEPTSCONCEPTS

Light is dual in nature. It has the Light is dual in nature. It has the characteristics of both a particle and characteristics of both a particle and a wave.a wave.

Plato, Greek Philospher, thought that Plato, Greek Philospher, thought that light consisted of tiny light consisted of tiny particlesparticles which which could enter the eye to create a could enter the eye to create a sensation of vision.sensation of vision.

Phytagoras thought that light Phytagoras thought that light travels as tiny travels as tiny particlesparticles from a from a luminous object to the eye.luminous object to the eye.

Newton considered light as a tiny Newton considered light as a tiny particle called corpuscles sent out particle called corpuscles sent out by luminous bodies which behaves by luminous bodies which behaves like a tiny elastic ball. It travels in a like a tiny elastic ball. It travels in a straight line at enormous speed.straight line at enormous speed.

Christian Huygens thought that Christian Huygens thought that light is light is a form of transversea form of transverse wave wave motionmotion sent out by luminous bodies sent out by luminous bodies

James Clerk Maxwell thought light James Clerk Maxwell thought light is a result of the oscillations of the is a result of the oscillations of the electricallyelectrically charged particlescharged particles of the of the atomatom

Louis Victor de Broglie said that Louis Victor de Broglie said that light consisted of both particles and light consisted of both particles and waveswaves

Sources of LightSources of Light SUN=warms air,SUN=warms air, water, and land.water, and land. Fire=provides heat, light, Fire=provides heat, light,

and cooking fuel.and cooking fuel. Lightning=Lightning= Firefly=Firefly= Flashlight=Flashlight= Light bulb=Light bulb= Laser beams=Laser beams= Optical Optical telephone telephone fibers=fibers=**TraTrafficffic lilightsghts==

Properties of LightProperties of Light

1)1) Light travels in straight lines.Light travels in straight lines.

2)2) Shadows are formed when light is Shadows are formed when light is blocked by an object. It indicates that blocked by an object. It indicates that light travels in a straight line.light travels in a straight line.

3)3) Light travels much faster than sound. Light travels much faster than sound. Its speed is 3.0 x 10Its speed is 3.0 x 1088 meter per meter per second.second.

4)4) We see things because they reflect We see things because they reflect light into our eyes.light into our eyes.

Light travels in Light travels in straightstraight lines: lines:

Laser

ShadowsShadows

Shadows are places where light is “blocked”:

Rays of light

Light travels Light travels much fastermuch faster than sound. than sound. For example:For example:

1) Thunder and lightning start at the same time, but we will see the lightning first.

2) When a starting pistol is fired we see the smoke first and then hear the bang.

When light reaches an object, it When light reaches an object, it is absorbed, reflected, or passes is absorbed, reflected, or passes through it. These objects are: through it. These objects are:

Transparent object allows all light rays to Transparent object allows all light rays to pass through. Examples: glass, plastic pass through. Examples: glass, plastic covercover

Translucent object allows only few light Translucent object allows only few light rays to pass through because others are rays to pass through because others are reflected and absorb by the object. reflected and absorb by the object. Examples: tented glassExamples: tented glass

Opaque object does not allow light to Opaque object does not allow light to pass through. Examples: book, block of pass through. Examples: book, block of woodwood

Transparent objects:Transparent objects:

The windows on a school bus,The windows on a school bus, A clear empty glass,A clear empty glass, A clear window pane,A clear window pane, The lenses of some The lenses of some

eyeglasses,eyeglasses, Clear plastic wrap,Clear plastic wrap, The glass on a clock,The glass on a clock, A hand lens,A hand lens, Colored glass…Colored glass… ALL of these are ALL of these are transparent.transparent.

Yes, we can see through them Yes, we can see through them because light passes through because light passes through each of them.each of them.

Translucent objectsTranslucent objects Thin tissue paper,Thin tissue paper, Waxed paper,Waxed paper, Tinted car windows,Tinted car windows, Frosted glass,Frosted glass, Clouds,Clouds, All of these All of these

materials are materials are translucent and translucent and allow some light to allow some light to pass but the light pass but the light cannot be clearly cannot be clearly seen through. seen through.

Opaque objects:Opaque objects: Heavy weight paper,Heavy weight paper, CardboardCardboard Aluminum foil,Aluminum foil, Mirror, bricks, buildings,Mirror, bricks, buildings, Your eyelids and hands,Your eyelids and hands, Solid wood door,Solid wood door, All of these objects are All of these objects are

opaqueopaque because light because light cannot pass through cannot pass through them at all.them at all.

They cast a dark They cast a dark shadow.shadow.

We see things because they We see things because they reflectreflect light into our eyes: light into our eyes:

Homework

Luminous and non-luminous Luminous and non-luminous objectsobjects

A luminous object is one that produces its own light.

A non-luminous object is one that reflects light.

Luminous objects Non Luminous objects

ReflectionReflection

It is the bouncing of light ray upon It is the bouncing of light ray upon hitting a surface.hitting a surface.

It may be regularly or irregularly It may be regularly or irregularly reflected.reflected.

Law of Reflection states that :Law of Reflection states that : The incident ray, normal line and the The incident ray, normal line and the

reflected ray lie on the same plane.reflected ray lie on the same plane. The angle of incidence is equal to the The angle of incidence is equal to the

angle of reflection.angle of reflection.

Types of ReflectionTypes of Reflection

Regular/Clear Reflection is a Regular/Clear Reflection is a reflection of light from a smooth reflection of light from a smooth surface. It is the reason why we see surface. It is the reason why we see our image in front of a mirror.our image in front of a mirror.

Diffuse Reflection is a reflection from Diffuse Reflection is a reflection from a rough surface. It enables us to read a rough surface. It enables us to read the text in the newspaper and see an the text in the newspaper and see an object under the shade of the tree.object under the shade of the tree.

Clear vs. Diffuse ReflectionClear vs. Diffuse Reflection

Smooth, shiny Smooth, shiny surfaces have a surfaces have a clearclear reflection: reflection:

Rough, dull surfaces have a diffuse reflection.

Diffuse reflection is when light is scattered in different directions

REFLECTIONREFLECTION Reflection from a mirror:Reflection from a mirror:

Incident ray

Normal

Reflected ray

Angle of incidence

Angle of reflection

Mirror

The Law of ReflectionThe Law of Reflection

Angle of incidence = Angle of Angle of incidence = Angle of reflectionreflection

The same !

!!

Activity 1Activity 1 : : “Just Passing Through:”“Just Passing Through:”

What happens when light strikes glass? Or What happens when light strikes glass? Or

waxed paper? Or a bookwaxed paper? Or a book?? If light travels through If light travels through

an object it is an object it is ==transparenttransparent

If light is blocked by If light is blocked by an object and a dark an object and a dark shadow is cast it is= shadow is cast it is= opaque.opaque.

If some light passes If some light passes through but not all through but not all and a light shadow is and a light shadow is present it present it is=is=translucent.translucent.

Activity 2Activity 2 : : What happens when light hits What happens when light hits these objects? Identify it as transparent, these objects? Identify it as transparent, opaque or opaque or translucent. translucent.

Glass of water Glass of water School bus School bus

windowwindow Notebook paperNotebook paper Waxed paperWaxed paper Plastic wrapPlastic wrap Tissue paperTissue paper CardboardCardboard TextbookTextbook Hand lens…Hand lens…

Activity 3 : Let’s find out how light travels?Activity 3 : Let’s find out how light travels? Simple Activity: 1 working flashlightSimple Activity: 1 working flashlight 1. Shine a flashlight on a wall.1. Shine a flashlight on a wall. 2. Does light from the flashlight reach the wall? How do you 2. Does light from the flashlight reach the wall? How do you

know?know? 3. Place an object between the flashlight and the wall. Shine the 3. Place an object between the flashlight and the wall. Shine the

object with the flashlight. What do you notice?object with the flashlight. What do you notice? 4.Write your observations in your journal.4.Write your observations in your journal. 5. What evidence do you have showing light travels in a 5. What evidence do you have showing light travels in a

straight line?straight line? 6.Record answers in your science journal6.Record answers in your science journal 7.Move closer with the flashlight. 7.Move closer with the flashlight. 8. Any changes? 8. Any changes?

Activity 4 : Write a story about light.Activity 4 : Write a story about light.

AssessmentAssessment

Pencil and paper testPencil and paper test Use rubric for the student’s Use rubric for the student’s

performance during the activity, performance during the activity, writing of the activity report and the writing of the activity report and the story of lightstory of light

Sample TestSample Test

1. Consider the diagram below. Which one of the 1. Consider the diagram below. Which one of the angles angles

(A, B, C, or D) is the angle of incidence? Which (A, B, C, or D) is the angle of incidence? Which one of the angles is the angle of reflection? one of the angles is the angle of reflection?

2. A ray of light is incident towards a 2. A ray of light is incident towards a plane mirror at an angle of 30-plane mirror at an angle of 30-degrees with the mirror surface. degrees with the mirror surface. What will be the angle of reflection? What will be the angle of reflection?

3. If a bundle of parallel incident rays 3. If a bundle of parallel incident rays undergoing diffuse reflection follow undergoing diffuse reflection follow the law of reflection, then why do the law of reflection, then why do they scatter in many different they scatter in many different directions after reflecting off a directions after reflecting off a surface?  surface?  

4. Is it easier to read from pages of a 4. Is it easier to read from pages of a book which are rough or from pages book which are rough or from pages which are smooth and glossy? which are smooth and glossy? Explain your answer. Explain your answer.