Class 12/Wave Optics/CBSE
Newton’s Corpuscular Theory
| 1. | Theory / Scientist | Newton’s Corpuscular Theory |
| 2. | Approx. period | 1670s |
| 3. | Basic idea about light | Light consists of tiny particles (corpuscles) emitted by luminous bodies. |
| 4. | Main evidence / explanation | Straight-line propagation of light and reflection could be explained using particle motion. |
| 5. | Major success | Explained reflection and attempted to explain refraction. |
| 6. | Main limitation | Could not satisfactorily explain interference, diffraction and polarization. Predicted light travels faster in denser media (wrong). Could not explain why light travels slower in water than air. |
Huygens’ Wave Theory
| 1. | Theory / Scientist | Huygens’ Wave Theory |
| 2. | Approx. period | 1678 |
| 3. | Basic idea about light | Light is a longitudinal wave propagating through a hypothetical medium called “ether.” |
| 4. | Main evidence / explanation | Huygens’ principle: every point on a wavefront acts as a source of secondary wavelets. |
| 5. | Major success | Explained reflection, refraction and wave phenomena. |
| 6. | Main limitation | The assumed ether medium was problematic; could not explain the later-established electromagnetic nature of light. Could not explain polarization (requires transverse waves). Could not explain the photoelectric effect. |
Young’s Double-Slit Experiment
| 1. | Theory / Scientist | Young’s Double-Slit Experiment |
| 2. | Approx. period | 1801s |
| 3. | Basic idea about light | Demonstrated the wave nature of light through interference patterns. |
| 4. | Main evidence / explanation | Constructive & destructive interference. Proved light behaves as a wave. |
| 5. | Main limitation | Did not explain the photoelectric effect. Still relied on the ether concept. |
Maxwell’s Electromagnetic Theory
| 1. | Theory / Scientist | Maxwell’s Electromagnetic Theory |
| 2. | Approx. period | 1860s |
| 3. | Basic idea about light | Light is a transverse electromagnetic wave consisting of oscillating electric and magnetic fields. |
| 4. | Main evidence / explanation | Maxwell’s equations predicted electromagnetic waves travelling at the speed of light. |
| 5. | Major success | Unified optics and electromagnetism and explained polarization. |
| 6. | Main limitation | Classical EM theory could not explain blackbody radiation, photoelectric effect and atomic spectra. |
Hertz Experiment
| 1. | Theory / Scientist | Hertz’s Experiment |
| 2. | Approx. period | 1887s |
| 3. | Basic idea about light | Confirmed Maxwell’s theory by generating and detecting electromagnetic waves. |
| 4. | Main evidence / explanation | Proved light is an EM wave. Showed radio waves travel at speed of light. |
| 5. | Main limitation | Did not address the photoelectric effect. |
Planck’s Quantum Theory
| 1. | Theory / Scientist | Planck’s Quantum Theory |
| 2. | Approx. period | 1900 |
| 3. | Basic idea about light | Energy is emitted or absorbed in discrete packets (quanta): E = hν. |
| 4. | Main evidence / explanation | Energy exchange between matter and radiation occurs in quantized amounts. |
| 5. | Major success | Explained blackbody radiation and introduced the quantum concept. |
| 6. | Main limitation | Initially treated quantization mainly as an energy-exchange principle rather than a complete theory of light. |
Einstein’s Photon Theory
| 1. | Theory / Scientist | Einstein’s Photon Theory |
| 2. | Approx. period | 1905 |
| 3. | Basic idea about light | Light consists of discrete packets called photons, each having energy E = hν. |
| 4. | Main evidence / explanation | Photoelectric effect: photons transfer their energy to electrons. |
| 5. | Major success | Explained the photoelectric effect and particle-like behaviour of light. |
| 6. | Main limitation | Classical wave properties still require a wave description. |
Compton Effect
| 1. | Theory / Scientist | Compton Effect |
| 2. | Approx. period | 1923s |
| 3. | Basic idea about light | X-ray photons collide with electrons, transferring momentum like particles. |
| 4. | Main evidence / explanation | Confirmed photon momentum Strong evidence for particle nature. |
| 5. | Main limitation | Only applicable to high-energy photons. |
de Broglie’s Matter-Wave Theory
| 1. | Theory / Scientist | de Broglie’s Matter-Wave Theory |
| 2. | Approx. period | 1924 |
| 3. | Basic idea about light | Matter particles also have wave nature; wavelength λ = h/p. |
| 4. | Main evidence / explanation | Proposed wave nature for moving particles such as electrons. |
| 5. | Major success | Led to the concept of matter waves and was confirmed by electron diffraction experiments. Explained Bohr’s quantized orbits. Basis for quantum mechanics. |
| 6. | Main limitation | Initially no experimental proof (confirmed later by Davisson-Germer). |
The overall evolution
Corpuscles → Waves → Electromagnetic waves → Quanta/photons → Wave–particle duality
The modern view is that light has wave–particle duality:
- Wave nature: interference, diffraction, polarization
- Particle nature: photoelectric effect, Compton effect, photon interactions
- Photon energy: E = hν
- Photon momentum: p = h/λ
- de Broglie matter wavelength: λ = h/p
Important distinction: de Broglie’s theory is primarily about the wave nature of matter, whereas Planck and Einstein established the quantum/particle aspects of radiation.
https://edu-physics.com/notes/class-xii/wave-optics/
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