Polytechnic 2nd Semester Applied Physics-II Notes: Chapter- Light

Polytechnic 2nd Semester Applied Physics-II Notes: Physics serves as the fundamental basis for all core subjects in technology. For Diploma holders in engineering and technology, studying Physics is indispensable, as it cultivates a comprehensive comprehension of physical phenomena, a scientific mindset, and engineering aptitude. 

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Polytechnic 2nd Semester Applied Physics-II Notes

The Applied Physics curriculum encompasses fundamental concepts that find practical application in various industries. Consequently, the teaching of Physics is incorporated into the first and second semesters across all disciplines of Diploma Engineering. In this post, we share Polytechnic 2nd Semester Applied Physics-II Notes: 

Polytechnic 2nd Semester Applied Physics-II Chapter 1 Notes 

Polytechnic 2nd Semester Applied Physics-II chapter 1 is Light. 

1. Introduction to Light:

   - Light is a form of electromagnetic radiation that is visible to the human eye.

   - It is composed of tiny particles called photons, which are massless and travel in waves.

   - The speed of light in a vacuum is approximately 299,792 kilometers per second (km/s).

2. Properties of Light:

   - Reflection: Light can bounce off the surface of an object, following the law of reflection.

   - Refraction: Light can change direction as it passes from one medium to another, due to a change in its speed.

   - Absorption: Light can be absorbed by matter, converting its energy into heat or other forms of energy.

   - Transmission: Light can pass through certain materials, such as glass or air, without being absorbed or reflected.

   - Interference: When two or more light waves meet, they can interact and create patterns of constructive or destructive interference.

3. Behavior of Light Waves:

   - Wavelength: The distance between two consecutive points in a light wave, typically measured in nanometers (nm).

   - Frequency: The number of wave cycles passing a given point per second, measured in hertz (Hz).

   - Amplitude: The height or intensity of a light wave, which determines its brightness or loudness.

   - Electromagnetic Spectrum: Light waves span a wide range of wavelengths, forming the electromagnetic spectrum that includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.

4. The Nature of Visible Light:

   - Visible light is the portion of the electromagnetic spectrum that our eyes can detect.

   - It consists of different colors, ranging from red (longest wavelength) to violet (shortest wavelength).

   - The visible spectrum can be separated and observed using a prism or a diffraction grating.

   - White light is a mixture of all the visible spectrum colors.

5. Applications of Light:

   - Vision: Light is crucial for human and animal vision, enabling us to see the world around us.

   - Optics: Light is used in various optical technologies, such as lenses, microscopes, telescopes, cameras, and lasers.

   - Communication: Light is utilized in fiber optic cables for high-speed data transmission over long distances.

   - Energy: Sunlight is a primary source of energy for plants through the process of photosynthesis.

   - Medicine: Light-based therapies like laser surgery and photodynamic therapy are used in medical treatments.

6. Quantum Nature of Light:

   - According to quantum theory, light exhibits both wave-like and particle-like properties, known as wave-particle duality.

   - The quantization of light energy is explained by photons, which behave as discrete packets of energy.

   - Light can exhibit phenomena like diffraction and interference, which are characteristic of waves.

Polytechnic 2nd Semester Applied Physics-II Syllabus Light Chapter Notes

Polytechnic 2nd Semester Applied Physics-II Syllabus Sub-Topic Notes

Topic: Recapitulation of Reflection of Light

Reflection is the phenomenon of the bouncing back of light when it encounters a surface. It follows the law of reflection, which states that the incident ray, the reflected ray, and the normal to the surface at the point of incidence, all lie in the same plane. The angle of incidence is equal to the angle of reflection.

Topic: Reflection from Spherical Mirrors

Spherical mirrors are mirrors with a curved surface, either concave or convex. When light rays strike a spherical mirror, they undergo reflection according to the laws of reflection. In a concave mirror, the reflecting surface is curved inward, while in a convex mirror, the reflecting surface is curved outward.

Topic: Idea of Real and Virtual Images

When light rays meet or appear to meet at a point after reflection from a mirror, an image is formed. The image can be classified as real or virtual. A real image is formed when the reflected rays actually converge at a point. It can be captured on a screen. On the other hand, a virtual image is formed when the reflected rays appear to diverge from a point. It cannot be captured on a screen.

Topic: Mirror Formula

The mirror formula is a mathematical equation that relates the object distance (u), the image distance (v), and the focal length (f) of a spherical mirror. It is given by:

1/f = 1/v + 1/u

where f is positive for a convex mirror and negative for a concave mirror.

Topic: Sign Convention

The sign convention is used to assign positive or negative values to the distances involved in spherical mirror calculations. In the sign convention:

- Distances measured in the direction of incident light are taken as positive.

- Distances measured opposite to the direction of incident light are taken as negative.

- The focal length of a convex mirror is positive, while for a concave mirror, it is negative.

Topic: Nature, Position, and Size of Images for Different Positions of Object for a Concave and Convex Mirror

The nature, position, and size of the image formed by a spherical mirror vary based on the position of the object. 

For a concave mirror:

- When the object is placed beyond the center of curvature, the image is real, inverted, and diminished in size.

- When the object is placed at the center of curvature, the image is real, inverted, and of the same size.

- When the object is placed between the center of curvature and the focus, the image is real, inverted, and magnified.

- When the object is placed at the focus, the reflected rays are parallel, and no image is formed.

- When the object is placed between the focus and the mirror, the image is virtual, erect, and magnified.

For a convex mirror:

- The image formed by a convex mirror is always virtual, erect, and diminished in size, regardless of the position of the object.

Understanding the principles of reflection, the types of mirrors, the formation of images, and the calculations involved help us comprehend the behavior of light and the properties of spherical mirrors in various scenarios.

Title: Exploring the Wonders of Light: Refraction, Total Internal Reflection, and Optical Fiber Applications


Light, the electromagnetic radiation that allows us to see and perceive the world around us, possesses fascinating properties. Among these are refraction, total internal reflection, and their remarkable application in optical fibers. 

In this article, we will delve into the concepts of refraction, refractive index, critical angle, and total internal reflection, and explore how these principles are harnessed in the design and function of optical fibers.

Refraction of Light:

When light travels from one medium to another, such as from air to water or from air to glass, it undergoes a change in direction. This phenomenon is known as refraction. The bending of light occurs due to the change in its speed as it passes through different materials. The extent of this bending depends on the refractive indices of the two mediums involved.

Refractive Index:

The refractive index is a measure of how much light is slowed down or refracted when it passes through a particular substance. It is defined as the ratio of the speed of light in a vacuum to the speed of light in the medium under consideration. Different materials have different refractive indices, which determine the degree of bending or refraction experienced by light as it passes through them.

Critical Angle and Total Internal Reflection:

As light passes from a denser medium to a less dense medium, such as from water to air, it bends away from the normal (an imaginary line perpendicular to the surface). At a specific angle of incidence, known as the critical angle, the refracted light ray travels along the boundary between the two mediums. Beyond this critical angle, if the angle of incidence is increased further, total internal reflection occurs.

Total internal reflection happens when the angle of incidence exceeds the critical angle, and all the light is reflected back into the original medium instead of being refracted. This phenomenon is particularly significant when light tries to pass from a denser medium to a less dense medium.

Relationship between Critical Angle and Refractive Index:

The critical angle is determined by the refractive indices of the two mediums involved. The relationship between the critical angle (θc) and the refractive indices (n1 and n2) is given by Snell's law:

n1sin(θc) = n2sin(90°) = n2

The critical angle is inversely proportional to the refractive indices of the two mediums. This relationship highlights the significance of refractive indices in determining the angle at which total internal reflection occurs.

Optical Fiber: Application of Total Internal Reflection:

Optical fibers are thin, flexible strands made of transparent materials, such as glass or plastic, designed to transmit light over long distances. They rely on the principle of total internal reflection to guide and contain the light within the fiber.

An optical fiber consists of a core, which is the central region through which light travels, and a cladding, which surrounds the core. The core has a higher refractive index compared to the cladding. 

When light enters the core at an angle greater than the critical angle, it undergoes total internal reflection and continues to bounce off the core-cladding interface, ensuring that the light remains confined within the core.

Acceptance Angle:

The acceptance angle of an optical fiber is the maximum angle at which light can enter the fiber and still undergo total internal reflection. If the incident angle exceeds the acceptance angle, some of the light may escape the core, resulting in a loss of signal integrity. Therefore, maintaining the acceptance angle is crucial for efficient light transmission through the fiber.


Disclaimer: Remember to refer to textbooks or additional resources for a more comprehensive understanding of light and its various aspects.

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