Fundamental Physics Concepts: Semiconductors and Optics
PN Junction: Diffusion, Drift, and Barrier Potential
1. Diffusion Current: Due to the concentration gradient, majority carriers move across the junction (holes from the p-side to the n-side and electrons from the n-side to the p-side). This motion constitutes the diffusion current.
2. Drift Current: The electric field in the depletion region causes minority carriers to move across the junction (holes from the n-side to the p-side and electrons from the p-side to the n-side). This is called drift current.
Read MoreEssential Concepts in Alternating Current and Wave Optics
Alternating Current (AC)
AC (L-7): The current which changes continuously with time and reverses its direction periodically is called AC. The instantaneous AC is given by I = I0 sin ωt.
DC: The current which is unidirectional (constant) is called DC.
RMS of AC over a complete cycle: It is defined as the square root of the mean of the square value of AC over a complete cycle. i.e., Irms = I0 / √2 = 0.707 I0.
Impedance: The combined opposition offered by reactance and resistance to the flow of alternating
Read MoreClassical and Quantum Free Electron Theory Principles
1. Classical Free Electron Theory and Assumptions
The classical free electron theory explains the electrical behavior of metals by assuming that a metal consists of a lattice of positive ions surrounded by a gas of free electrons. These electrons move freely inside the metal and obey classical Newtonian mechanics. Electron–electron interactions are neglected, and collisions occur only with fixed ions. The electrons follow Maxwell–Boltzmann statistics, and an applied electric field causes a net
Read MorePrinciples of Light Reflection and Refraction
Image Formation by Mirrors and Lenses
1. If reflected or refracted rays never meet, the image is virtual because the rays only appear to meet when extended backward. This occurs in plane and convex mirrors, in diverging lenses, or in converging lenses when the object is inside the focal point (F).
Refraction Fundamentals
2a. Refraction is the bending of light as it changes speed moving between media.
2b. Rules for Bending Light:
- (1) Low $\to$ high density = toward the normal.
- (2) High $\to$ low density
Semiconductor Devices Principles: PN Diode, LED, Solar Cell, APD
Here is a detailed explanation of the principle, construction, and working of the following semiconductor devices:
PN Junction Diode
LED (Light Emitting Diode)
Solar Cell
Avalanche Photodiode
1. PN Junction Diode
Principle
A PN junction diode works on the principle of unidirectional current conduction — it allows current to flow in forward bias but blocks it in reverse bias.
Construction
Made by joining P-type and N-type semiconductors.
A depletion region forms at the junction due to diffusion of electrons
Astronomy Fundamentals: Celestial Bodies and Space Travel
Astronomy Fundamentals and Timekeeping
Ancient people used the Sun, Moon, stars, and tools like sundials to track time and seasons.
- A solstice is the longest or shortest day of the year.
- An equinox is when day and night are equal in length.
Models of the Universe
Understanding the structure of the cosmos evolved over time:
- The geocentric model states Earth is at the center of the universe.
- The heliocentric model states the Sun is at the center and planets orbit it.
- Elliptical orbits mean planets move in