Nature of Light

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Useful websites

 * 1) Interactive Simulation on Nature of Light So_what_is_light.png In this simulation, you can explore the history of quantum physics, how the understanding of light was developed and an overview of the theories of light. Source: NSTA
 * 2) Interactive Simulation on Nature of Light light_as_waves.png In this simulation you can explore the behaviour of light as waves. Source: NSTA
 * 3) Wikipedia article on Wave Particle Duality
 * 4) Web interactives and additional information on Physics of Light and Colour; Source: Olympus Microscopy Research
 * 5) Physics Classroom-Electromagnetic Waves
 * 6) Physics Classroom-Wavelike Properties of Light
 * 7) Physics Classroom - Electromagnetic Radiation and Visible Spectra

Reference Books

 * 1) E=m$$c^2$$ by David Bodanis - This book is a very interesting account of how the understanding developed in quantum physics and the theory of light.  See Online


 * 1) NCERT Textbook Chapter Light
 * 2) NCERT Textbook Chapter Reflection and Refraction
 * 3) NCERT Textbook Chapter Human Eye and the Colourful World

An image of a concept map of light
http://karnatakaeducation.org.in/KOER/en/images/7/73/Light_Resource_Material_Subject_Teacher_Forum_September_2011_Concept_Map.jpg

= Teaching Outlines =

Learning objectives

 * 1) White Light is made up of seven constituent colours
 * 2) Introduction to the corpuscular theory of light

Notes for teachers
Reinforce the learning from activity on Recombination of Colours. Also understand the model as proposed by Newton on the nature of light and examine the limitations of this theory.

Activity No # 1A - Using a prism to split and combine white light
White paper, Pins, Source of Light, Prisms, Dark room
 * Estimated Time - 2 periods of 40 minutes
 * Materials/ Resources needed
 * Prerequisites/Instructions, if any
 * 1) Activity on Recombination of Colours
 * 2) Dark room for light experiments
 * Multimedia resources
 * Website interactives/ links/ simulations
 * Process (How to do the activity)
 * 1) Demonstrate the dispersion using a prism and recombination of the light
 * 2) Students must do this experiment in groups
 * 3) The teacher must demonstrate carefully how to position the prism, how to observe rays in light experiments
 * 4) Students must be able to draw ray diagrams showing the split of the spectrum
 * Developmental Questions (What discussion questions)
 * 1) When the light falls on the prism, what did you expect to see? What happened?
 * 2) What are the colours you see? What is the order of the colours?
 * Evaluation (Questions for assessment of the child)
 * 1) From the incoming beam of light, which colour showed the maximum angle of dispersion? (This question can be picked up later to discuss wavelengths and electromagnetic spectrum)
 * 2) If you change the direction of the incoming light, what happens to the dispersion?
 * 3) Observe the accuracy of the diagrams
 * Question Corner

Activity No # 1B - What is colour
The objective is to understand colours as different wavelengths associated with light. Computer, projector, power
 * Estimated Time - 30 minutes
 * Materials/ Resources needed
 * Prerequisites/Instructions, if any
 * Multimedia resources

Watch the video and discuss with the student their understanding. Draw a ray diagram to show how this theory explains reflection.
 * Website interactives/ links/ simulations
 * Process (How to do the activity)
 * Developmental Questions (What discussion questions)
 * 1) How does a wave move? The vocabulary is wave propagation)
 * 2) What gets transmitted?
 * 3) What can you say about the wave when the frequency is high?
 * 4) What can you say about the wave when the wavelength is high?
 * 5) It is possible to look at light as a wave; the waves are not of material objects but travelling waves changing electric and magnetic fields.
 * 6) Different wavelengths are associated with different energy levels and different kind of radiation(light is a form of electromagnetic radiation; there are other electromagnetic radiations)
 * 7) The higher the frequency the higher the energy; this is seen as different colours of the visible spectrum
 * 8) Can we break down these seven colours more? (No; demonstrate with a prism; these are pure colours)
 * Evaluation (Questions for assessment of the child)
 * Question Corner

Activity No # 1C - Corpsucular Theory of Light
The objective is to study Newton's theory on light Computer, projector, power Watch the video and discuss with the student their understanding. Draw a ray diagram to show how this theory explains reflection.
 * Estimated Time - 30 minutes
 * Materials/ Resources needed
 * Prerequisites/Instructions, if any
 * Multimedia resources
 * Website interactives/ links/ simulations
 * Process (How to do the activity)
 * Developmental Questions (What discussion questions)
 * 1) Can reflection and refraction be explained using this? How?
 * 2) Newton said that different colours can be caused by different sizes of particles. Knowing what you know of the eye, explain how this would have worked.
 * 3) What do you not understand about this theory based on your observations?
 * Evaluation (Questions for assessment of the child)
 * Question Corner

Learning objectives

 * 1) Light behaves like waves
 * 2) Light undergoes reflection, refraction, interference and diffraction - all those that we associate with waves
 * 3) Light is an electromagnetic radiation that travels as a wave and does not need a medium
 * 4) As in any other wave, the energy depends on the frequency of the wave
 * 5) When light waves are of different wavelengths, they are seen as different colours

Notes for teachers
Studies done on how light travels has helped us visualise it now as changing electrical magnetic fields that interact with other material objects as packets of energy. This radiation can be thought of as waves of different wavelengths. The waves are not of material objects but travelling waves changing electric and magnetic fields. Different wavelengths are associated with different energy levels and different kind of radiation.

Click here for more notes on the nature of light, visible light and colours.

Videos on Nature of Light The following videos are useful in understanding the nature of light.
 * 1) Nature of Light
 * 2) Thomas Young's Double Slit Experiment

Activity No # 1- Reflection, Refraction and Diffraction as waves
The objective is to demonstrate how we can explain the phenomena of light - reflection, refraction - through the wave model. The teacher must reconcile the rays to the wave model. Computer, Projector, Blackboard Simulation of the double slit experiment Source:Olympus Microscopy Centre After discussing the simulation, explain the process of reflection and refraction in waves Observe the student response to above questions
 * Estimated Time - 40 minutes
 * Materials/ Resources needed
 * Prerequisites/Instructions, if any
 * Multimedia resources
 * Website interactives/ links/ simulations
 * Process (How to do the activity)
 * Developmental Questions (What discussion questions)
 * 1) Have you seen any waves?
 * 2) When they encounter an obstruction what do they do? (They bounce back, they bend around, etc_
 * 3) In this image, what do you see happening to the wavefronts - they get reflected, they get refracted
 * 4) How can we represent this using a ray diagram?
 * Evaluation (Questions for assessment of the child)
 * Question Corner

Activity No # 2 - Simulation of double slit experiment
The objective of this activity is to demonstrate an important experiment from the 18th century that made physicists rethink about the nature of light. Until this time, Newton's corpuscular theory was used to explain light.
 * Estimated Time
 * Materials/ Resources needed
 * Prerequisites/Instructions, if any
 * Multimedia resources
 * Website interactives/ links/ simulations
 * Process (How to do the activity)
 * 1) Launch the simulation from the PhET website or download it and run. #Discuss the simulation with the following questions.
 * 2) Do the simulation with water and then light. You can do sound if students have been introduced to material waves and understand sound.  It is better to do another simulation on wave propagation on sound before doing this simulation.
 * Developmental Questions (What discussion questions)
 * 1) Let us click on water here. When a drop of water drips in a bucket, what do you expect to see (waves move around)
 * 2) If two drops of water drip, what do you expect to see (the patterns the water make will intersect; this is called interference)
 * 3) Now let us do a similar thing with light
 * 4) What do you see now from the source of the light? (Light emanating)
 * 5) If I put one slit, what will I expect to see, according to the ray theory of light? (There will be a dark spot where the slit is but rest of the screen will have light)
 * 6) If I have two slits, what will I expect to see?
 * 7) What do we really observe? Why would this be?
 * 8) Talk about how waves propagate and what happens when there is interference?


 * Evaluation (Questions for assessment of the child)
 * Question Corner

Activity No # 3- Explain the double slit experiment
Computer, Projector, Blackboard Simulation of the double slit experiment Source:Olympus Microscopy Centre After discussing the simulation, explain the process of interference in waves Observe the student response to above questions
 * Estimated Time - 40 minutes
 * Materials/ Resources needed
 * Prerequisites/Instructions, if any
 * Multimedia resources
 * Website interactives/ links/ simulations
 * Process (How to do the activity)
 * Developmental Questions (What discussion questions)
 * 1) What is a wave? (carries energy)
 * 2) Can two waves meet? (Water, ropes etc)
 * 3) What happens when they meet? The energy increases or decreased
 * 4) The interaction between two waves is called interference
 * 5) This can be constructive or destructive interference
 * Evaluation (Questions for assessment of the child)
 * Question Corner

Learning objectives

 * 1) It is possible to look at light and other electro magnetic radiation as a wave or as a particle known as the photon.
 * 2) Light travels as electromagnetic radiation; with waves of different wavelengths
 * 3) Light interacts with material particles in discrete packets called photons
 * 4) Different wavelengths are associated with photons of different energies

Notes for teachers
The objective here is to enable students to understand that light can be thought of as a wave or as particles. Different models of light explain different phenomena. It is important to get a sense of the history of how light was understood, how electromagnetism was understood and how light is the result of continuously oscillating electric and magnetic fields.

Activity No #1 - Introduce the nature of electromagnetic radiation

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 * Developmental Questions (What discussion questions)
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 * Question Corner

Activity No #

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Notes for teachers
These are short notes that the teacher wants to share about the concept, any locally relevant information, specific instructions on what kind of methodology used and common misconceptions/mistakes.

Activity No #

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 * Process (How to do the activity)
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 * Question Corner

Activity No #

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 * Question Corner

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 * 1) It is possible to look at light and other electro magnetic radiation as a wave or as a particle known as the photon.
 * 2) Light travels as electromagnetic radiation; with waves of different wavelengths
 * 3) Light interacts with material particles in discrete packets called photons
 * 4) Different wavelengths are associated with photons of different energies