 Physics Lecture Resources

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Physics Lecture Resources
Prof. Mineesh Gulati Head-Physics Wing Happy Model Hr. Sec. School, Udhampur, J&K Website: happyphysics.com happyphysics.com

Ch 33 The Nature and Propagation of Light
© 2005 Pearson Education

33.1 The Nature of Light Speed of light=2.9792458x108m/s
Wave front: describe wave propagation Rays Rays Source Wave fronts Wave fronts © 2005 Pearson Education

Physical optics: the branch dealing specifically with wave behavior
Geometric optics: the branch of optics which is used for the ray description. Physical optics: the branch dealing specifically with wave behavior © 2005 Pearson Education

33.2 Reflection and Refraction
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Reflection and Refraction
Incident rays Normal θa θb θr Refracted rays Reflected rays © 2005 Pearson Education

Type of reflection index of refraction © 2005 Pearson Education

law of reflection law of refraction
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wavelength of light in a material
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Example 33.2 The wavelength of the red light form a helium-neon laser is 633nm in air but 474nm in aqueous humor inside your eyeball. Calculate the index of refraction of the aqueous humor and the speed and frequency of the light in this substance. ANS: © 2005 Pearson Education

33.3 Total Internal Reflection
θb Θb=90° nb na >θcrit θcrit θa P critical angle for total internal reflection © 2005 Pearson Education

Application of total internal reflection
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33.4 Dispersion The dependence of wave speed and index of refraction on wavelength is called dispersion © 2005 Pearson Education

Dispersion of light by a prism
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Rainbow © 2005 Pearson Education

33.5 Polarization Polarization is a characteristic of all transverse waves. Polarized in y-direction Polarized in z-direction © 2005 Pearson Education

Polarizing filter © 2005 Pearson Education

A Polaroid filter is illuminated by unpolarized natural light
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Malus’s law, polarized light passing through an analyzer
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Polarization by reflection
Reflected light is 100% polarized perpendicular to the plane of incidence Polarization by reflection Natural light Normal Plane of incidence Reflecting surface Transmitted light is partially polarized parallel to the place of incidence

Brewster’s law for the polarizing angle
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33.6 Scatttering of Light When we look at the daytime sky, the light that we see is sunlight that has been absorbed and then re-radiated in a variety of directions. The process is called scattering. © 2005 Pearson Education

AA’ construct a new wave front BB’
33.7 huygens’ Principle Every point of a wave front may be considered the source of secondary wavelets that spread out in all directions with a speed equal to the speed of propagation of the wave. AA’ construct a new wave front BB’ © 2005 Pearson Education

Light is an electromagnetic wave
Light is an electromagnetic wave. When emitted or absorbed, it also shows particle properties. It is emitted by accelerated electric charges. The speed of light is a fundamental physical constant. © 2005 Pearson Education

A wave front is a surface of constant phase; wave fronts move with a speed equal to the propagation speed of the wave. A ray is a line along the direction of propagation, perpendicular to the wave fronts. Representation of light by rays is the basis of geometric optics. © 2005 Pearson Education

When light is transmitted from one material to another, the frequency of the light is unchanged, but the wavelength and wave speed can change. The index of refraction n of a material is the ratio of the speed of light in vacuum c to the speed v in the material. If λ0 is the wavelength in a vacuum, the same wave has a shorter wavelength λ in a medium with index of refraction n. (See Example 33.2) © 2005 Pearson Education

At a smooth interface between two optical materials, the incident, reflected, and refracted rays and the normal to the interface all lie in a single plane called the plane of incidence. The law of reflection states that the angles of incidence and reflection are equal. The law of refraction relates the angles of incidence and refraction to the indices of refraction of the materials. Angles of incidence, reflection, and refraction are always measured from the normal to the surface. (See Examples 33.1 and 33.3) © 2005 Pearson Education

When a ray travels in a material of greater index of refraction na toward a material of smaller index nb, total internal reflection occurs at the interface when the angle of incidence exceeds a critical angle ncrit. (See Example 33.4) © 2005 Pearson Education

The variation of index of refraction n with wavelength λis called dispersion. Usually, n decreases with increasingλ. © 2005 Pearson Education

The direction of polarization of a linearly polarized electromagnetic wave is the direction of the E- field. A polarizing filter used as an analyzer, the intensity Imax of the light transmitted through the analyzer depends on the angle φbetween the polarization direction of the incident light and the polarizing axis of the analyzer. (See Example 33.5) © 2005 Pearson Education

When unpolarized light strikes an interface between two materials, Brewster’s law states that the reflected light is completely polarized perpendicular to the plane of incidence (parallel to the interface) if the angle of incidence equals the polarizing angle . (See Example 33.6) © 2005 Pearson Education

Light is scattered by air molecules
Light is scattered by air molecules. The scattered light is partially polarized. © 2005 Pearson Education

Huygens’ principle states that if the position of a wave front at one instant is known, the position of the front at a later time can be constructed by imagining the front as a source of secondary wavelets. Huygens’ principle can by used to derive the laws of reflection and refraction. © 2005 Pearson Education

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