A Lesson Plan in Physics LIGHT Prepared by: Evelyn S. Lauron Paknaan National High School

OBJECTIVES: Describe nature of light Identify and describe transparent, translucent and opaque objects Differentiate luminous and non luminous bodies Define and describe reflection

SUBJECT MATTER: LIGHT

CONCEPTS Light is dual in nature. It has the characteristics of both a particle and a wave. Plato, Greek Philospher, thought that light consisted of tiny particles which could enter the eye to create a sensation of vision.

Phytagoras thought that light travels as tiny particles from a luminous object to the eye. Newton considered light as a tiny particle called corpuscles sent out by luminous bodies which behaves like a tiny elastic ball. It travels in a straight line at enormous speed.

Christian Huygens thought that light is a form of transverse wave motion sent out by luminous bodies James Clerk Maxwell thought light is a result of the oscillations of the electrically charged particles of the atom Louis Victor de Broglie said that light consisted of both particles and waves

Sources of Light SUN=warms air, water, and land. Fire=provides heat, light, and cooking fuel. Lightning= Firefly= Flashlight= Light bulb= Laser beams= Optical telephone fibers= *Traffic lights=

Properties of Light Light travels in straight lines. Shadows are formed when light is blocked by an object. It indicates that light travels in a straight line. Light travels much faster than sound. Its speed is 3.0 x 108 meter per second. We see things because they reflect light into our eyes.

Light travels in straight lines: Laser

Shadows Shadows are places where light is “blocked”: Rays of light

Light travels much faster than sound. For example: 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 is absorbed, reflected, or passes through it. These objects are: Transparent object allows all light rays to pass through. Examples: glass, plastic cover Translucent object allows only few light rays to pass through because others are reflected and absorb by the object. Examples: tented glass Opaque object does not allow light to pass through. Examples: book, block of wood

Transparent objects: The windows on a school bus, A clear empty glass, A clear window pane, The lenses of some eyeglasses, Clear plastic wrap, The glass on a clock, A hand lens, Colored glass… ALL of these are transparent. Yes, we can see through them because light passes through each of them.

Translucent objects Thin tissue paper, Waxed paper, Tinted car windows, Frosted glass, Clouds, All of these materials are translucent and allow some light to pass but the light cannot be clearly seen through.

Opaque objects: Heavy weight paper, Cardboard Aluminum foil, Mirror, bricks, buildings, Your eyelids and hands, Solid wood door, All of these objects are opaque because light cannot pass through them at all. They cast a dark shadow.

We see things because they reflect light into our eyes: Homework

Luminous and non-luminous objects A luminous object is one that produces its own light. A non-luminous object is one that reflects light. Non Luminous objects Luminous objects

Reflection It is the bouncing of light ray upon hitting a surface. It may be regularly or irregularly reflected. Law of Reflection states that : The incident ray, normal line and the reflected ray lie on the same plane. The angle of incidence is equal to the angle of reflection.

Types of Reflection Regular/Clear Reflection is a reflection of light from a smooth surface. It is the reason why we see our image in front of a mirror. Diffuse Reflection is a reflection from a rough surface. It enables us to read the text in the newspaper and see an object under the shade of the tree.

Clear vs. Diffuse Reflection Smooth, shiny surfaces have a clear reflection: Rough, dull surfaces have a diffuse reflection. Diffuse reflection is when light is scattered in different directions

REFLECTION Reflection from a mirror: Mirror Normal Angle of incidence Incident ray Reflected ray Angle of incidence Angle of reflection Mirror

Angle of incidence = Angle of reflection The Law of Reflection Angle of incidence = Angle of reflection The same !!!

Activity 1 : “Just Passing Through:” What happens when light strikes glass? Or waxed paper? Or a book? If light travels through an object it is =transparent If light is blocked by an object and a dark shadow is cast it is= opaque. If some light passes through but not all and a light shadow is present it is=translucent.

Activity 2 : What happens when light hits these objects Activity 2 : What happens when light hits these objects? Identify it as transparent, opaque or translucent. Glass of water School bus window Notebook paper Waxed paper Plastic wrap Tissue paper Cardboard Textbook Hand lens…

Activity 3 : Let’s find out how light travels? Simple Activity: 1 working flashlight 1. Shine a flashlight on a wall. 2. Does light from the flashlight reach the wall? How do you know? 3. Place an object between the flashlight and the wall. Shine the object with the flashlight. What do you notice? 4.Write your observations in your journal. 5. What evidence do you have showing light travels in a straight line? 6.Record answers in your science journal 7.Move closer with the flashlight. 8. Any changes? Activity 4 : Write a story about light.

Assessment Pencil and paper test Use rubric for the student’s performance during the activity, writing of the activity report and the story of light

Sample Test 1. Consider the diagram below. Which one of the angles (A, B, C, or D) is the angle of incidence? Which one of the angles is the angle of reflection?

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

3. If a bundle of parallel incident rays undergoing diffuse reflection follow the law of reflection, then why do they scatter in many different directions after reflecting off a surface?   4. Is it easier to read from pages of a book which are rough or from pages which are smooth and glossy? Explain your answer.