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Book: “University Physics” by Young & Freedman 13th Edition

The Nature & propagation of light1. The nature of light2. Reflection3. Refraction4. Total internal Reflection5. Fiber optics

Physics-II (Ph-1002)

WEEK # 1

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1. The Nature of Light

Visible Light which is visible to the human eye and is responsible for the sense of sight.

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Brief History

• In 1690 Huygens proposed that light have wave nature.

• In 1704 Isaac Newton said light is composed of little particles or corpuscles.

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• In 1801 Thomas Young experimentally proved that light is wave.

• In 1815 A.J. Fresnel also approved wave nature of light.

• In 1864 James Clark Maxwell gave his electromagnetic theory.

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• In 1886 Heinrich Hertz also confirmed Electromagnetic Theory.

• 1900 Max Planck proposed that electromagnetic radiation is quantized.

• In 1905 Einstein extended the Quantum theory of Max Planck and said light consist of quanta or photons.

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Dual Nature of Light

• In 1924 Louis de Broglie predicted that light have a dual nature, In some situations it behaves like wave, and in others like particles.

• Each photon has energy

E = h ƒh (Planck’s constant) = 6.63 x 10-34 J s,

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Electromagnetic WavesThe electric and magnetic waves are perpendicular to each other, and to the direction of propagation

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EM Spectrum

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The Visible Spectrum

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Wave Fronts & RaysWave fronts are parallel surfaces connecting equivalent

points on adjacent waves. While rays show the direction of propagation.

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2. ReflectionAt the interface between two mediums Light returns back to the medium from which it originated. Example: The reflection of trees in river.

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Types of Reflection1. Specular ReflectionReflection from a smooth surface

Example: Mirror

2. Diffuse ReflectionReflection from a rough surface

Example: A rough path or road.

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3. Refraction

Change in direction of propagation of a wave due to a change in its transmission medium.Example: Pencil appears to be bent in water

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Refraction

• If angle of incidence is greater than angle of refraction, ray bends toward the normal

• If angle of incidence is smaller than angle of refraction, ray bends away from the normal

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Index of Refraction

Speed of light in vacuum divided by speed of light in any other medium (e.g. water)

Index of refraction= n= c/v

• N is a Unit less quantity• n is 1 for vacuum and air.• n is greater than 1 for any other material.

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Laws of Reflection & Refraction

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4. Total Internal ReflectionA phenomenon that happens when a propagating wave strikes a medium boundary at an angle larger than a particular critical angle with respect to the normal to the surface.

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Example

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5. Fiber Optics• A technology that uses glass (or plastic) threads (fibers) to

transmit data.• A fiber optic cable consists of a bundle of glass threads, each

of which is capable of transmitting messages modulated onto light waves.

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How it works?• n (refractive index) for glass is greater than the

surroundings (air e.g.)

• If all angles exceed critical angle the light is trapped inside the cable. (Total internal reflection)

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What is Inside Optical Fibers?

1. Core: 8 µm diameter

2. Cladding: 125 µm dia.

3. Buffer: 250 µm dia

4. Jacket: 400 µm dia.

Condition: ncore>nclad

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Parts of Optical Fiber

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Uses of Fiber Optics

• Medical: Used as light guides, imaging tools and also as lasers for surgeries

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Endoscope

• Endoscope: an instrument used to examine the interior of a hollow organ or cavity of the body. Unlike most other medical imaging devices, endoscopes are inserted directly into the organ.

• Endoscopy: means looking inside and typically refers to looking inside the body for medical reasons.

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Types of Endoscopy• Amnioscopy - examination of the amniotic cavity and fetus.• Arthroscopy - examination of the joints.• Bronchoscopy - examination of the air passages and the lungs.• Colonoscopy - examination of the colon.• Colposcopy - examination of the cervix and the tissues of the vagina and vulva.• Cystoscopy - examination of the urinary bladder.• EGD (Esophageal Gastroduodenoscopy), also known as panendoscopy - examination of the

esophagus, stomach and duodenum.• ERCP (endoscopic retrograde cholangio-pancreatography) - examination of the liver,

gallbladder, bile ducts, and pancreas.• Fetoscopy - examination of the fetus.• Laparoscopy - a small incision to examine the abdominal cavity.• Laryngoscopy - examination of the back of throat, including voice box (larynx) and vocal cords.• Proctoscopy - examination of the rectum and the end of the colon.• Rhinoscopy - examination of the inside of the nose.• Thoracoscopy - examination of the lungs or other structures in the chest cavity.

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That’s all for today !