Nature of Light

The Story of Science

Philosophy of Science

Teaching of Science

Curriculum and Syllabus

Topics in School Science

Textbooks

Question Bank

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Concept Map

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Textbook

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Additional information

Useful websites

1. Interactive Simulation on Nature of Light
   
   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
   
   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

Teaching Outlines

Concept #1 - White Light is made up of colours

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.

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Activity No # 1A - Using a prism to split and combine white light

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• Estimated Time - 2 periods of 40 minutes
• Materials/ Resources needed

White paper, Pins, Source of Light, Prisms, Dark room

• Prerequisites/Instructions, if any

1. Activity on Recombination of Colours
2. Dark room for light experiments

• Multimedia resources
• Website interactives/ links/ simulations

Newton's Prism Experiment. This is a demonstration of the experiment showing the splitting and recombination of white light. Useful to show the students after the demonstration/ experimentation in class.

• 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

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The objective is to understand colours as different wavelengths associated with light.

• Estimated Time - 30 minutes
• Materials/ Resources needed

Computer, projector, power

• Prerequisites/Instructions, if any
• Multimedia resources

• Website interactives/ links/ simulations
• Process (How to do the activity)

Watch the video and discuss with the student their understanding.

• 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)

Draw a ray diagram to show how this theory explains reflection.

• Question Corner

Concept #2 - Wave Nature of Light

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

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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.

• Estimated Time - 40 minutes
• Materials/ Resources needed
  

Computer, Projector, Blackboard

• Prerequisites/Instructions, if any
  

Students must have done simple optics experiments on reflection and refraction.

• Multimedia resources
• Website interactives/ links/ simulations

Source:Olympus Microscopy Centre

• Process (How to do the activity)

After discussing the simulation, explain the process of reflection and refraction in waves

• 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)

Observe the student response to above questions

• Question Corner

Activity No # 2 - Simulation of double slit experiment

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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

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• Estimated Time - 40 minutes
• Materials/ Resources needed
  

Computer, Projector, Blackboard

• Prerequisites/Instructions, if any
  

Simulation of the double slit experiment

• Multimedia resources
• Website interactives/ links/ simulations

Source:Olympus Microscopy Centre

• Process (How to do the activity)

After discussing the simulation, explain the process of interference in waves

• 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)

Observe the student response to above questions

• Question Corner

Concept #3 - Particle Nature of Light

Learning objectives

1. One of the early theories of light was that light is made of particles
2. Particle theory explains reflection and refraction; light travels in a straight line of particles
3. Particle theory (corpuscular theory) did not explain diffraction especially at small, microscopic scale
4. Discovery of photoelectric Effect provided the evidence for particle nature when all evidence was showing that light was a wave

Notes for teachers

The view among scientists on light was split between wave and particle nature of light. Issac Newton proposed his corpuscular theory while Christian Huygens proposed that light is a wave. Reflection and refraction can be explained using particle theory of light and geometric optics supported the particle theory of light.

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

Activity No # 1 - Corpsucular Theory of Light

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The objective is to study Newton's theory on light

• Estimated Time - 30 minutes
• Materials/ Resources needed

Computer, projector, power

• Prerequisites/Instructions, if any
• Multimedia resources

• Website interactives/ links/ simulations
• Process (How to do the activity)

Watch the video and discuss with the student their understanding.

• 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)

Draw a ray diagram to show how this theory explains reflection.

• Question Corner

Activity No # 2- Reflection, Refraction and Diffraction as particles

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• Estimated Time - 45 minutes
• Materials/ Resources needed

Computer, projector, power

• Prerequisites/Instructions, if any

Students must have done simple optics experiments on reflection and refraction.

• Multimedia resources
• Website interactives/ links/ simulations

• Process (How to do the activity)

1. Demonstrate the tutorial and discuss the following questions 1-5
2. Show the diffraction tutorial and discuss the other questions

• Developmental Questions (What discussion questions)

1. When particles hit a surface, what do you expect to see? (Bounce, reflection)
2. When particles enter a surface, what do you expect to see? (They slow down, change direction, etc)
3. Can you visualize reflection and refraction as particles?
4. Based on the evidence so far - reflection and refraction, which theory of light better explains the behaviour of light
5. If in a dark room there is a single bulb on the wall and we put a partition in front of the light, will the room be completely dark behind the partition?
6. What happens in the light bulb case? How is the light getting spread in the room? Can light (travelling in a straight line) bend around the partition?
7. If you imagine waves of light, how would you explain this (think of waves of water)?
8. Now what is your conclusion about the theory of light?

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

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.

Concept # 3- Dual Nature of Light

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.

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Activity No #1 - Introduce the nature of electromagnetic radiation

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• Process (How to do the activity)
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• Evaluation (Questions for assessment of the child)
• Question Corner

Activity No #

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• Question Corner

Concept #4 Electromagnetic Spectrum

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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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• 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