Brief Summary
Alright guys, this video is a quick guide for some important questions for your Applied Physics II exam. Sachin bhaiya is sharing some key topics that could help you score well, even if you haven't been able to attend all the classes. Key topics discussed include:
- Laser (including Helium Neon Laser)
- Optical Fiber
- PN Junction Diode
- Types of Magnetic Materials
Introduction
Sachin bhaiya welcomes everyone back to the channel and mentions that he will be discussing some important questions for the Applied Physics II exam. He acknowledges that he couldn't take full classes but aims to provide a video that will cover questions worth 15-20 marks. He encourages viewers to practice these questions and mentions that downloading the Gyan with Sachin application is beneficial for accessing notes and previous year question papers. He also mentions joining the Telegram channel for PYQ papers from 2018-2023. Students of any branch in the second semester can access notes for all subjects at a nominal price on the app.
Laser
The video discusses lasers, including the full form (Light Amplification by Stimulated Emission of Radiation). A laser is a device that emits a very intense, monochromatic (single-color) and highly parallel beam of light. To create a laser, a medium is placed in a chamber. This chamber has one side that is 100% reflective and another side that is partially reflective. When a photon strikes an excited atom in the chamber, it releases another photon of the same frequency. This process repeats, creating many photons of the same frequency. These photons then exit through the partially reflective side, forming a laser beam.
Laser Applications and Characteristics
Laser beams are used in communication between Earth and the Moon, measuring distances, increasing computer storage, and in medical procedures like LASIK surgery. Sachin bhaiya shares his personal experience of getting LASIK done. Lasers are also used for cutting hard materials and in 3D photography. Key characteristics of laser beams are that they are in phase, monochromatic (one color), nearly parallel, narrow, and highly intense. If you write about lasers in this way, you can score good marks.
Helium Neon Laser
The video explains the Helium-Neon laser, which is a type of gas laser that emits light at a wavelength of 6328 angstroms. It consists of a quartz tube with a diameter of about 1 cm, filled with a mixture of neon (0.1 mm pressure) and helium (1 mm pressure). One end of the tube is fully reflective, and the other is partially reflective. A generator excites the gas mixture with a high frequency, causing helium atoms to reach a high energy level and emit photons. These photons bounce between the mirrors and create more photons, eventually exiting through the partially reflective end as a laser beam.
Optical Fiber
Optical fiber is a thin strand used to transmit information from one place to another. It consists of a core, cladding, and a jacket. The core is the inner part with a diameter of 6 to 250 micrometers, made of glass or plastic. The cladding surrounds the core and has a lower refractive index. The jacket protects the fiber. The principle behind optical fiber is total internal reflection. Light entering the fiber at a certain angle is reflected back into the core, allowing it to travel long distances. Optical fibers are used to transmit electrical signals as light, using infrared waves for long distances and visible light for shorter distances. The thinner the optical fiber, the better its efficiency.
Optical Fiber Classification
Optical fibers are classified into single-mode and multi-mode fibers. Single-mode fibers transmit light in a straight line, while multi-mode fibers allow light to travel in multiple paths. Multi-mode fibers are further divided into step index and graded index fibers. In step index fibers, there is a sudden change in refractive index between the core and cladding. In graded index fibers, the refractive index of the core gradually decreases from the center to the edge. Graded index fibers are used to reduce signal distortion. Optical fibers are used in optical communication systems, are immune to electromagnetic interference, and are useful in measuring physical quantities. They have applications in medical monitoring, remote sensing, sensors, networking, and telecommunications.
PN Junction Diode
A PN junction diode is formed by joining a P-type semiconductor with an N-type semiconductor. The junction between them is called the PN junction. The symbol for a PN junction diode shows an arrowhead pointing from the P region to the N region. The diode has two characteristics: forward bias and reverse bias. In forward bias, the positive terminal of the battery is connected to the P side, and the negative terminal to the N side. In reverse bias, the connections are reversed. PN junction diodes are used in power rectifiers, signal diodes, voltage stabilization, and computer logic circuits.
Types of Magnetic Materials
The video discusses types of magnetic materials: diamagnetic, paramagnetic, and ferromagnetic. Diamagnetic substances are weakly magnetized in the opposite direction of the magnetic field. Each atom has a zero magnetic moment. Examples include bismuth, water, and copper. Paramagnetic substances are weakly magnetized in the same direction as the magnetic field. They are slightly attracted to strong magnets. Ferromagnetic substances are strongly attracted to magnets and become strongly magnetized in the direction of the field. Examples include cobalt, steel, and chromium.
Difference Between Magnetic Materials
The video highlights the differences between diamagnetic, paramagnetic, and ferromagnetic materials. Diamagnetic materials exist in solid, liquid, and gaseous states, while ferromagnetic materials exist only in crystalline solids. Diamagnetic materials have an even number of electrons, paramagnetic have an odd number, and ferromagnetic materials are arranged in domains. Diamagnetic materials are slightly repelled by magnetic fields, paramagnetic are slightly attracted, and ferromagnetic are strongly attracted. The video also covers how their magnetic properties change in a magnetic field and after the field is removed, as well as their magnetic susceptibility and permeability.
Conclusion
Sachin bhaiya concludes the video, hoping that the explanation of these three to four topics was helpful. He mentions that he has his own exams and hasn't been able to upload many videos, but he plans to cover subjects like BMC, General Engineering, and Mechanics in more detail after the 4th. He encourages viewers to stay connected with the channel for more content and to consider purchasing notes for other subjects.
