Wave-Particle Duality

Wave-Particle Duality of Light

• This module explores the dual nature of light, its properties, behavior, and optical phenomena.
• Some properties of light are explained by its wave nature (interference, diffraction, scattering).
• Other properties are explained by its particle nature (photoelectric effect).
• Some properties require considering light as both wave and particle (reflection, refraction, dispersion).
• The module also includes wave-like characteristics of electrons and how Hertz produced radio pulses based on predecessors knowledge.

Intended learning outcomes

• Describe wave and particle models explain: light propagation, reflection and refraction.
• Explain how the photon concept and photon energy explain: red light use in darkrooms, ultraviolet sunburns but not visible light, and color perception.
• Cite experimental evidence: electrons behave like waves.
• Differentiate: dispersion, scattering, interference, diffraction.
• Explain various light phenomena such as: reflections in spoons, mirages, light passing through cellophanes, color changes in different lights, rainbows, haloes, white/dark clouds, blue sky/red sunsets.
• Describe how Hertz produced radio pulses.

Republic Act 8293

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• Government approval is needed to exploit work for profit.
• The agency can require royalty payments.

How to Learn

• Use a pen and journal.
• Read carefully and take notes of key information.
• Follow instructions in activities and exercises.
• Perform activities with dedication and record observations.
• Answer tests and exercises honestly.
• Ask your teacher for clarification if needed.

The Nature of Light

• Scientists have disagreed on whether light is matter or energy, a wave or a particle.
• The lesson describes how wave and particle models explain propagation, reflection, and refraction.

Observing a Ball's Path

• Observe the path of a ball thrown slowly and quickly to understand trajectory.
• A slow ball will curve due to gravity, while a fast ball moves in a straighter line; similar to Newton's ideas of light as particles.

Light Behavior

• Light travels straight in a vacuum until it interacts with something.
• Light can then be absorbed, reflected, refracted, scattered, or transmitted.

Corpuscular Theory

• Newton believed light is made of particles traveling in straight lines.
  • Reflection: Particles collide and bounce off surfaces.
  • Refraction: Attraction between medium molecules and light particles causes speed changes.
  • Diffraction: Newton explains observed diffraction effects as particles interacting rather than light bending corners.
  • Dispersion: Particles of different mass are affected differently during refraction.

Wave Theory

• Christian Huygens proposed light is a wave.
• He argued that particles would collide and cancel each other if light beams crossed.
  • Huygens' Principle: Each point on a wave acts as a source for new waves moving in the direction of wave motion.
  • Reflection: Light bounces off an object, creating a reversed image.
  • Refraction: Wave bends when speed changes entering a new medium, causing a change in direction.
  • Diffraction: Light bends based on relative size of wavelength to opening.

Behavior of Light Summary

• Phenomena can be explained by particle or wave properties.
  • Reflection: Both wave and particle.
  • Refraction: Both wave and particle.
  • Interference: Wave.
  • Diffraction: Wave.
  • Polarization: Wave.
  • Photoelectric effect: Particle.

Exploring How Light Travels Activity

• Observe shadows in your yard.
• Note how shadows change.
• Take selfies in different directions, noting when you get a good photo.
• Share your best/worst selfie with a group.

Energy of Light

• Colors are frequencies of light emitted or reflected, not substances themselves.
• Learning will explain photon concept, and use energy explains red light use in darkrooms, UV causing sunburn, and how colors are visible.

Arranging Rainbow Colors Activity

• Arrange rainbow colors in order of increasing frequency and energy.

Light and Energy

• Newton thought light comprised corpuscles; light behaves like energy packets called quanta or photons.
• Photoelectric effect proves light has particle properties.
• Photons emit when atoms' electrons are excited.

Atomic Excitation

• When light hits an atom, electrons gain energy and jump to higher levels.
• Electrons emit photons of specific frequencies, creating colored lines called atomic spectra, which are unique to each element.

Electromagnetic Spectrum

• The electromagnetic spectrum contains all types of light.
• Most light in the universe is invisible to humans.
• Visible light makes up only a small portion of the electromagnetic spectrum.
• Other types of light include radio waves, microwaves, infrared/ultraviolet radiation, X-rays and gamma rays.

Relationship between energy and frequency in light

• Described via E = hf (E = energy; h = Planck's constant [6.63 x 10^-24 joules-second]; f = frequency).

Ultraviolet Light.

• High-frequency UV light causes sunburn.

Red Light

• Darkrooms utilize red light for its low frequency and energy.

How Colors are Seen

• Visible light has different frequencies, determining color.
• Colors are perceived as objects absorb some colors and reflect/transmit others.
• White objects reflect all colors, while black objects absorb all.

Life and Electromagnetic Waves

• Radio waves: communications, remote controls, MRI; requires controls for band use.
• Microwaves: communications, ovens, radar, deep heating; cell phone use.
• Infrared: thermal imaging, heating, absorbed by atmosphere; greenhouse effect.
• Visible light: all pervasive, photosynthesis/human vision.
• Ultraviolet: sterilization, cancer control, Vitamin D production; ozone depletion/cancer causing.
• X-rays: medical security, medical diagnosis/cancer therapy, cancer causing.
• Gamma rays: nuclear medicine/security, medical diagnosis/cancer therapy; cancer causing/radiation damage.

Wave Properties of Electrons

• Physicist Louis de Broglie created the concept that light can behave as particles AND waves
• Electrons may also exhibit wave-like properties like frequency/wavelength

Matching Light to its Properties

• Using red light in darkrooms corresponds to lower frequency and lower energy.
• Getting sunburned corresponds to higher frequency and higher energy in ultraviolet light.
• Seeing a white t-shirt as blue relates to higher frequency and higher energy.

Planck's Constant

• Max Planck uncovered a constant which he added to his radiation laws in 1900.

Particle and Wave

• Albert Einstein showed light (electromagnetic wave) acted as particles in 1905.

Compton Effect

• Arthur Holly Compton's effect in 1922 showed light is a wave-particle duality.

Electron Properties

• Louis de Broglie proposed in 1924 that electrons and matter may have wave properties.

Proof of Electron Waves

• Clinton Davisson and Lester Germer confirmed electron wave nature in 1927.

Complementary Relationship

• Niels Bohr announced the aspect of wave and particle relation in 1928.

Heisenberg Uncertainty Principle

• Electron position and momentum cannot both be measured exactly at the same time.

Shrodinger's Equations

• Erwin Schrodinger formed equations for electrons, showing electrons in orbits form standing waves.
• The greatest probability of presence for said electrons would be in areas that are densest, while the lowest chance of presence is the opposite

Properties of Light

• Properties are explained by the light being reflected and/or refracted

Am I Dispersed? Activity

• Perform rainbow experiment with prism and light.
• Light separates when it enters an object acting like prism.
• Dispersion separates white light into colors ranging from 400 nm (violet) to 700 nm (red).
• Dispersion depends on difference in refractive index.

Rainbow Formation

• Rainbows form after rain when water droplets act as prisms, splitting sunlight into colors.

Atmospheric Phenomena

• Light scattering causes the blue sky and horizon.
• Tiny atmosphere particles scatter sunlight.
• Violet has the shortest wavelength, scattered the most.
• The eyes are not sensitive to indigo, so blue appears most.
• Red light can be seen when the sun is in the horizon.

What's More

• Water droplets compose clouds.
• Smaller droplets scatter most colors resulting in white clouds.
• Larger, denser droplets absorb light more creating dark rain clouds.

Explaining Colors

• Interference on soap bubbles creates the rainbow effect.
• Interference results from waves meeting and demonstrating either constructive (brighter image) or destructive (dark bands) interactions.

Fresnel Diffraction

• Looking at light through a small hole between fingers makes a white and dark vertical bond

Hertz

• Heinrich Rudolf Hertz was the first to transmit/receive radio wave.

James Clerk Maxwell

• James clerk theory of light was approved due to Hertz.

Hertz's accomplishments

• The scientific unit of frequency is his namesake, "hertz."
• Hertz proved the wireless phenomena transmission with experimental instruments.He created components with polished brass knobs connected together with an induction coil that had gaps for sparks to ignite between them.

Explanation of Hertz's apparatus

• Hertz added a spark-gap to an already existing spark gap and would use this new induction coil along with a high voltage of alternating current, leading to a series of sparks at gap in intervals .
• Hertz noticed side-sparks form along the point of A and B or his new image.
• He would also note the side-sparks behavior, and change position point C. He found the AC wire segments of ACB had to match each other. If certain electrical waves in AC and BC had to match, and not be in sync with another. When there are differences with A and B then sparks would have the capacity to generate