Wave Optics | Class 12 Physics Notes
By ConceptScroll Team · Published on 17 July 2026 · 3 min read
Wave Optics – this guide gives you a concise, exam-ready overview of Wave Optics from Class 12 Physics, written by ConceptScroll editors and reviewed against the latest NCERT textbook.
10.1 INTRODUCTION
The chapter on Wave Optics begins with a historical overview of the models of light. In 1637, Descartes proposed the corpuscular model of light, which explained reflection and refraction by treating light as particles. According to this model, if a light ray bends towards the normal upon refraction, the speed of light in the second medium would be greater. Isaac Newton further developed this corpuscular theory in his book "Opticks," which popularized the particle nature of light for a long time.
In 1678, Christiaan Huygens proposed the wave theory of light, which provided a different explanation. The wave model predicted that if the refracted ray bends towards the normal, the speed of light in the second medium is less, contrary to the corpuscular model. This was experimentally confirmed by Foucault in 1850, who showed that light travels slower in water than in air, supporting the wave theory.
Despite its explanatory power, the wave theory was not immediately accepted because of Newton's authority and the belief that waves require a medium for propagation, while light travels through vacuum. The wave nature of light was firmly established by Thomas Young's interference experiment in 1801, which measured the wavelength of visible light to be extremely small (for example, yellow light has a wavelength of about 0.6 micrometers).
Because the wavelength of visible light is very small compared to the size of typical optical components, light can be approximated as traveling in straight lines, which is the basis of geometrical optics. Geometrical optics neglects the wave nature by assuming the wavelength tends to zero, and defines rays as paths of energy propagation.
Later, Maxwell's electromagnetic theory of light unified electricity, magnetism, and optics by predicting electromagnetic waves that propagate in vacuum at the speed of light. Maxwell showed that light waves are electromagnetic waves consisting of oscillating electric and magnetic fields that sustain each other, allowing propagation through vacuum.
This chapter focuses on the wave theory of light, starting with Huygens' principle to derive laws of reflection and refraction, then discussing interference based on superposition, diffraction based on Huygens-Fresnel principle, and finally polarization, which arises from the transverse nature of light waves.
📊 Diagram: Figure 10.1 (a) A diverging spherical wave emanating from a point source. The wavefronts are spherical; Figure 10.1 (b) At a large distance from the source, a small portion of the spherical wave can be approximated by a plane wave.
🔗 Connection: Leads to Section 10.2 where Huygens' principle is introduced to understand wavefront propagation and derive laws of reflection and refraction.
Frequently asked questions
Laser light is considered to be coherent because it consists of
coordinated waves of exactly the same wavelength
Four lenses of focal length + 15 cm and + 150 cm are available for making a telescope. To produce the maximum magnification, the focal length of the eyepiece should be
+15 cm
Diffraction pattern is obtained using red light. What happens when the red light is replaced by the blue light?
the diffraction band becomes narrow and crowded
. In young's double slit experiment, the fringe pattern as seen on the screen is
hyperbola
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