
	Trending ▼ ICSE CBSE 10th ISC CBSE 12th CTET GATE UGC NET Vestibulares ResFinder

ISC Class XII Notes 2025 : Physics (Don Bosco School, Liluah, Howrah)

16 pages, 63 questions, 0 questions with responses, 0 total responses,

	Havan Gupta	+Fave Message
	Profile Timeline Uploads

Home > havangupta > F Also featured on: School Page

Formatting page ...

PHYSICS PROJECT NAME: HAVAN GUPTA SECTION: D CLASS: XII ROLL NO.: 24 TOPIC: SEMICONDUTO R (SOLAR CELLS, LIGHT EMITTING DIODES) INTRODUCTION ring dealing with the Electronics, the bran ch of phy sics and enginee devices, has und ergo ne behaviour of electrons and thei r applications in troll ed flow of electrons remarkable advancements ove r the years. The con , enabling the creation of is essential for the operation of electronic circuits world. various technologies that have transformed our BR IEF HIS TO RY ifica nt shif t from The evolution of electronic devices has seen a sign uum tubes were bulky, vacuum tubes to solid-state semiconductors. Vac ductors are com pac t, power-hungry, and unreliable, whereas semicon transformed the field of energy-efficient, and reliable. This transition has faster, and mor e effic ient electronics, enabling the development of smaller, devices. y. Conductors, suc h as Solids can be classified bas ed on their conductivit tron flow. Insulators, on metals, have shared electrons that facilitate elec electron flow. the othe r hand, have bou nd electrons that resist conductivity. making them Semiconductors, like silicon, have intermediate on, sem icon duc tors can idea l for electronic devices. Und er thermal excitati tivity. generate free electrons, increasing thei r conduc -------- "" "' ,., ,,,1 ,_..,. .. , .'",..... ,,...,.,. . ~ I I I mad e them a cruc ial The unique properties of semiconductors have erat e con duc tivit y and com pon ent of mod ern electronics. With thei r mod ons, sem icon duc tors have ability to be manipulated through various excitati ic devices that have enabled the creation of a wid e range of electron revolutionized mod em technology. Wh FUNDAMENTALS Energy Band Description of Solids In solids, the proximity of electrons in neighbouring orbits causes their energy levels to vary, giving rise to energy bands. The valence band encompasses the energy levels of valence electrons, while the conduction band lies above it. The behaviour of electrons in these bands determines the material's conductivity. Classification of Solids Solids can be classified into three categories based on their energy band structure: 1. Conductors: Conduction band is partially filled or overlaps with valence band, allowing free electron movement. 2. Insulators: Conduction band is empty, and the energy gap is large (Eg > 3eV), preventing electron movement. 3. Semiconductors: Conduction band is empty, and the energy gap is relatively small (Eg < 3eV), allowing some electron movement due to thermal excitation. Semiconductors, like Si and Ge, have a small energy gap, enabling some valence electrons to cross into the conduction band at room temperature. This creates vacancies in the valence band, allowing conduction through both electrons in the conduction band and vacancies in the valence band. The conductivity of semiconductors is small at room temperature but can be manipulated through external factors. Semiconductors can be classified into two types: 1. Intrinsic Semiconductors: Pure semiconductors, like Si and Ge, with a small energy gap, enabling some valence electrons to cross into the conduction band at room temperature. It consumes less energy. Ex-Solar panels, sensors. 2. Extrinsic Semiconductors: Semiconductors doped with impurities, altering their electrical properties. Consumes more energy. Ex-diodes, amplifiers. Extrinsic semiconductors can be further classified into: - N-type Semiconductors: Doped with donor impurities, increasing the number of free electrons. - P-type Semiconductors: Doped with acceptor impurities, increasing the number of holes (positive charge carriers). Doping allows for control over the semiconductor's conductivity and is Eg=Energy gap Conduction in Intrinsic Semiconductors free electrons and Intrinsic semiconductors have equal numbers of Key poi nts include: holes, both contributing to current conduction. 1. Equal number of electrons and holes s 2. Current conduction by bot h electrons and hole 3. Holes behave like positively charged particles 4. Conductivity given by a = e{n. . + nh h) The image includes two diagrams illustrating: 1. Electron and hole flow in an intrinsic semiconductor 2. A blo ck of sem icon duc tor with applied potential difference currents, given by I The total current is the sum of electron and hole P-N JUNCTION I Solar cells, also known as photovoltaic (PV) cells, work on the principle of photovoltaic effect. PNJunction A PN junction is fonned by combining p-type and n-type semiconductors. In a p-type semiconductor, holes are the majority charge carriers, while in an n-type semico nductor, electrons are the majority charge carriers. When a p-type and n-type semiconducto r are joined, electrons from the n-side diffuse to the p-side, creating a depletion region. Forward Bias and Reverse Bias Forward Bias: When a p-n junction is forward-biased, the p-side is connected to a positive terminal, and the n-side is connected to a negative tenninal. This reduces the depletion region, allowing current to flow easily. Reverse Bias: When a p-n junction is reverse-biased, the p-side is connected to a negative terminal, and the n-side is connected to a positive tenninal. This increases the depletion region, making it difficult for current to flow. I BREAKDOWN IN PN JUNCTION If the reverse bias voltage across a pn junction diode is increased, at a particular voltage the reverse current suddenly increases to a large value. This phenomenon is called breakdown of the diode and the voltage at which it occurs is called the breakdown voltage. At this voltage, the rate of creation of hole electron pair is increased leading to the increased current. There are two main processes by which breakdown may occur. Q) Avalanche breakdown Qi) Zener breakdown Avalanche Breakdown It occurs in lightly doped pn junction in which depletion layer is thick. The holes in the n-side and the conduction electrons in the p-side are accelerated due to the reverse bias voltage. If these minority carriers acquire sufficient kinetic energy from the electric field and collide with a valence electron, the bond will be broken and the valence electron will be taken to the conduction band. Thus a hole-electron pair will be created. This electron hole pair in turn will accelerate and break more bonds. Breakdown occurring in this manner is called avalanche breakdown. Zener Breakdown Breakdown may also be produced by direct breaking of valence bonds due to high electric field. When breakdown occurs in this manner it is called zener breakdown. It occurs in heavily doped pn junction in which depletion layer is very thin, due to which electric field in the junction is very high even for a small reverse bias voltage. When the applied reverse bias voltage reaches closer to the Zener voltage, the electric field in the depletion region gets strong enough to pull electrons from their valence band. The valence electrons that gain sufficient energy from the strong electric field of the depletion region break free from the parent atom. In the zener breakdown region, a small increase in the voltage results in the rapid increase of the electric current. ZENER DIODE A zener diode, also known as a breakdown diode, is a heavily doped semiconductor device that is designed to operate in the reverse direction. When the voltage across the terminals of a zener diode is reversed and the potential reaches the Zener voltage (knee voltage), the junction breaks down and the current flows in the reverse direction. This effect is known as the Zener effect. A zener diode operates just like a normal diode when it is forward biased. However a small leakage current flows through the diode when connected in reverse biased mode. As the reverse voltage increases to the predetermined breakdown (V), current starts flowing through the diode. The current through the diode changes but voltage across it remains essentially constant. We know that when the ac input voltage of a rectifier fluctuates, its rectified output also fluctuates. To get a constant de voltage from the unregulated de output of a rectifier, we use a zener diode. The circuit diagram of a voltage regulator using a zener diode is shown in the figure. ## Half-Wave Rectifier and Full-Wave Rectifier: Definitions, Working Principles, and Applications ### Definitions - *Half-Wave Rectifier (HWR)*: A half-wave rectifier is an electronic device that converts Alternating Current (AC) to Direct Current (DC) by allowing only one half-cycle of the AC input voltage to pass through, producing a pulsating DC output. It uses a single diode to achieve this conversion 1 - *Full-Wave Rectifier (FWR)*: A full-wave rectifier converts the full cycle of alternating current into direct current. It can be implemented using two diodes (center-tapped transformer) or four diodes (bridge rectifier) 2. ### Working Principles - *Half-Wave Rectifier*: In a half-wave rectifier, the diode is forward-biased during the positive half-cycle of the AC voltage and reverse-biased during the negative half-cycle. This results in a pulsating DC output with only one peak per cycle. - *Full-Wave Rectifier*: Full-wave rectifiers, on the other hand, utilize both halfcycles of the AC input voltage, resulting in a smoother DC output with a higher average value. ### Key Characteristics and Formulas - *Half-Wave Rectifier*: - *Ripple Factor*: The ripple factor of a half-wave rectifier is 1.21, indicating a relatively high amount of AC component in the output. - *Efficiency*: The maximum efficiency of a half-wave rectifier is around 40.6%. - *RMS Value*: The RMS value of the load current for a half-wave rectifier is given by lrms = lm/2, where Im is the peak current. - *Form Factor*: The form factor is defined as the ratio of the RMS value to the average value of output voltage 3 1. ### Applications and Disadvantages - *Half-Wave Rectifier*: - *Applications*: Half-wave rectifiers are used in small power supplies, signal detection, and modulation applications. - *Disadvantages*: They have low efficiency, high ripple factor, and limited applications due to their pulsating DC output. - *Full-Wave Rectifier*: - *Applications*: Full-wave rectifiers are commonly used in power supplies, battery chargers, and other applications requiring a stable DC output. - *Advantages*: They offer higher efficiency, lower ripple factor, and smoother DC output compared to half-wave rectifiers 2 4 . Materials and Fabrication Of Solar Cell Silicon-Based Solar Cells Silicon is the most widely used material for solar cells due to its abundance, non-toxicity, and well-established manufacturing processes. Silicon-based solar cells can be categorized into: 1. *Monocrystalline silicon*: Known for high efficiency (up to 22%) and uniform appearance. 2. *Polycrystalline silicon*: Less expensive than monocrystalline, but slightly less efficient (up to 18%). Other Materials 1. *Cadmium Telluride (CdTe)*: Thin-film solar cells with high efficiency (up to 18%) and low production costs. 2. *Copper Indium Gallium Selenide (GIGS)*: Thin-film solar cells with high efficiency (up to 21 %) and flexibility. 3. *Perovskites*: Emerging material with high potential efficiency (up to 25%) and low production costs. 4. *Gallium Arsenide (GaAs)*: High-efficiency material used in concentrated photovoltaic systems. Fabrication Techniques 1. *Diffusion*: Process used to create p-n junctions in silicon solar cells. 2. *Deposition*: Techniques like sputtering, evaporation, and chemical vapor deposition (CVD) are used to deposit thin films. 3. *Etching*: Process used to pattern and texture solar cell surfaces. 4. *Passivation*: Techniques used to reduce surface recombination and improve efficiency. Challenges, Future Directions, and Applications Despite advancements, challenges persist: 1. *Efficiency limitations*: Theoretical limits to efficiency for different materials. 2. *Cost reduction*: Efforts to reduce production costs while maintaining efficiency. 3. *Future directions*: Research on new materials, architectures, and fabrication techniques to further improve efficiency and reduce costs. Solar cells have various applications: 1. *Residential and commercial power generation* 2. *Utility-scale power plants* 3. *Space and aerospace applications* 4. *Consumer electronics* These materials and fabrication techniques play a crucial role in determining the efficiency, cost, and performance of solar cells. Half wave rectifier Full wave rectifier ## Solar Panel and System Design ### Solar Panel Configuration and Design Solar panels are designed to maximize energy output while minimizing costs. Key considerations include: 1. *Module configuration*: Series and parallel connections of solar cells to achieve desired voltage and current. 2. *Panel layout*: Arrangement of modules to optimize energy output and reduce losses. 3. *Frame and mounting*: Structural design to ensure durability and flexibility in installation. ### Maximum Power Point Tracking (MPPTI MPPT algorithms optimize energy output by tracking the maximum power point of the solar panel array. Techniques include: 1. *Perturb and Observe (P&O)*: Iterative method to find the maximum power point. 2. *Incremental Conductance*: Method that uses the slope of the P-V curve to track the maximum power point. ### Inverter Technologies Inverters convert DC power from solar panels to AC power for grid connection or local consumption. Key technologies include: 1. *String inverters*: Centralized inverters for larger solar arrays. 2. *Microinverters*: Module-level inverters for improved efficiency and monitoring. 3. *Power optimizers*: DC-DC converters that optimize energy output at the module level. ### System Monitoring and Control Monitoring and control systems track performance, detect issues, and optimize energy output. Features include: 1. *Real-time monitoring*: Tracking of energy output, voltage, and current. 2. *Fault detection*: Identification of issues such as module failures or string faults. 3. *Remote monitoring*: Access to system performance data via web or mobile interfaces. ### Structure of a Solar Cell A solar cell typically consists of multiple layers, including: - *Antireflection Coating:* Reduces reflection of sunlight, increasing the amount of light absorbe d by the solar cell. - -i:-ranspar~nt Adh~sive Cover Glass:* Protects the solar cell from environmental factors while allowing sunlight to pass through. - *Front Contact:* Collects electrons generated by the solar cell. - *n-Type Semiconductor:* A type of semiconductor material that has an excess of electrons. - *p-Type Semiconductor:* A type of semiconductor material that has a deficiency of electrons (or "holes"). - *Back Contact:* Collects holes generated by the solar cell. ### Working Mechanism of Solar Cells The working mechanism of solar cells can be explained in the following steps: 1. *Sunlight Absorption:* Sunlight hits the solar cell, exciting electrons in the semicon ductor material. 2. *Excitation of Electrons:* The excited electrons flow through the front contact and into the external circuit. 3. *Flow of Holes:* The holes generated by the sunlight flow through the back contact and into the external circuit. 4. *Electric Current Generation:* The flow of electrons and holes creates an electric current. ### Principle of Solar Cells Solar cells operate based on the photovoltaic effect, which is the generation of charge carriers in a light-abs orbing material due to the absorption of light radiation. The photovol taic effect is the process by which light is converted into electrical energy. ### Construc tion of Solar Cells Solar cells are typically made from crystalline silicon, which consists of two layers: - *n-Type Semicon ductor Layer (Emitter):* This layer has an excess of electrons. - *p-Type Semicon ductor Layer (Base):* This layer has a deficiency of electrons (or "holes"). These layers are sandwiched together, forming a p-n junction. The ~u~ace o~ the solar cell is coated with an anti-reflection coating to minimize the loss of 1nc1dent light energy due to reflection. ## Solar Cells: Generating Electricity from Light Solar cells are devices that convert light into electrical energy through a process known as the photovoltaic effect. When radiations fall on the p-n junction of a solar cell, it generates an electromotive force (emf), enabling the cell to produce electricity. ### Types of Solar Cells There are two primary types of solar cells: p-type and n-type. Both types utilize a combination of p-type and n-type silicon, which together form the p-n junction. This junction is crucial for the operation of solar cells, as it allows for the separation of charge carriers generated by light absorption. ### Working Mechanism In solar cells, electron-hole pairs are generated near the junction due to the absorption of light. The electrons move towards the n-type silicon layer, while the holes move towards the p-type silicon layer. This separation of charge carriers is facilitated by the electric field present at the p-n junction. ### Collection of Charge Carriers The electrons reaching the n-side are collected by the front contact, while the holes reaching the p-side are collected by the back electrical contact. As a result, a potential difference is developed across the solar cell. When an external load is connected to the solar cell, photocurrent flows through it, enabling the cell to generate electricity. ### Formation of Solar Panels To increase the power output, many solar cells are connected in series or parallel to form solar panels or modules. This configuration allows for the generation of a higher voltage or current, making it suitable for various applications, including residential, commercial, and industrial power generation. By harnessing the energy from sunlight, solar cells offer a renewable and sustainable source of electricity, reducing our reliance on fossil fuels and Woricing Principle of a Solar Cell: - A solar cell is essentially a p--n junction that generates emf when solar radiation falls on it. - The generation of emf by a solar cell occurs due to three basic processes: 1. Generation of Electron-Hole Pairs: Electron-hole pairs are generated due to incident light photons with energy greater than the bandgap energy (E) close to the junction. 2. Separation of Electrons and Holes: The electrons and holes are separated due to the electric field of the depletion region. Electrons are swept to the n-side. and holes are swept to the p--side. 3. collection of Electrons and Holes: The electrons reaching then-side are collected by the front contact. and the holes reaching the p-side are collected by the back contact. This results in the p-side becoming positive and the n-side becoming negative, giving rise to a photo-voltage. Applications and Case Studies ### Residential and Commercial Solar Power Sys tems Residential and commercial solar pow er systems prov ide clean energy and reduce electricity bills. Benefits include: 1. *Energy savings*: Reduced electricity cost s for hom eowners and businesses. 2. *Increased property value*: Solar installations can increase property value. 3. *Environmental benefits*: Reduced greenhouse gas emissions and reliance on fossil fuels. ### Utility-Scale Solar Power Plants Utility-scale solar pow er plants generate large amo unts of electricity for the grid. Characteristics include: 1. *Large land requirements*: Utility-scale solar plan ts require significant land areas. 2. *High energy output*: Plants can generate hundred s of megawatts of electricity. 3. *Grid integration*: Plants must be designed to integ rate with the electrical grid. ### Space and Aerospace Applications Solar cells are used in space and aerospace applicat ions due to thei r reliability and efficiency. Examples include: 1. *Satellites*: Solar cells pow er satellites and othe r spacecraft. 2. *Space stations*: Solar cells provide pow er for spa ce stations. 3. *Planetary exploration*: Solar cells pow er rovers and othe r planetary exploration vehicles. ### Case Studies of Successful Solar Projects Successful solar projects demonstrate the potential of solar energy. Examples include: 1. *Large-scale solar farms*: Projects like the Pavaga da Solar Park in India or the Tengger Desert Solar Park in China. 2. *Residential solar installations*: Homeowners who have installed solar panels to reduce energy bills. 3. *Commercial solar projects*: Businesses that have installed solar panels to reduce energy costs and carbon footprint. These applications and case studies demonstrate the versatility and potential of solar energy. ## Advantages of Solar Cells - Renewable Energy Source : Solar cells harness energy from the sun, es providing a clean, renewable, and abund ant sourc e of power. This reduc reliance on finite fossil fuels and mitiga tes clima te change 1. g - clea n and Green : Solar cells produ ce no emissions or pollution, makin them an environmentally friendly option . - Reliable and Durable : Solar cells are designed to withs tand extre me weather condi tions and can last for 25 to 40 years or more with minimal maintenance. can - cost- Effec tive : While initial installation costs may be high, solar cells save mone y in the long run by reducing electricity bills and poten tially generating income through excess energy sales. r - Low Maintenance Costs : Solar cells require minimal upkeep, furthe reducing operational expenses. , from - "Versatile and Flexible : Solar cells can be used in various applications residential to commercial and industrial settings. noise durin g energy conversion, - silen t Operation : Solar cells produ ce no 4 3 2 . making them suitable for urban areas ## Disadvantages of Solar Cells - High Initial Cost*: The upfro nt cost of installing solar cells can be prohibitively expensive for some individuals or businesses. and - *Weather Dependent*: Solar cells generate less powe r on cloud y days y cease to function at night, making them less reliable than traditional energ sources. to - *Space Requirement*: Solar cells require a significant amou nt of space generate substantial amounts of electricity. tally - Environmental Impact*: While solar cells themselves are environmen ts, friendly, their production process can have negative environmental impac such as waste generation. - *Storage and lntermittency*: Solar energy storage soluti ons can be g the expensive, making it challenging to store excess energ5y6generated durin 2 day for use at night or during periods of low sunlight Light Emitting Diodes (LEDs) A Light Emitting Diode (LED) is a type of semiconductor device that emits light when an electric current passes through it. LEDs are widely used in various applications, including lighting, displays, and indicators. ### Working Principle LEDs work on the principle of electroluminescence, where the recombination of electrons and holes in the semiconductor material releases energy in the form of light. The color of the light emitted depends on the energy gap of the semiconductor material used. ### Characteristics - Low Power Consumption : LEDs consume low power and are energy-efficient. - Long Lifespan : LEDs have a long lifespan and can operate for thousands of hours. - High Brightness : LEDs are highly bright and can be used in a variety of lighting applications. - Environmentally Friendly : LEDs are free of toxic materials like mercury and lead, making them environmentally friendly. ### Applications - ughting : LEDs are used in various lighting applications, including residential, commercial, and industrial lighting. - Displays : LEDs are used in displays, such as LED lVs, LED monitors, and LED signs. - indicators : LEDs are used as indicators in various applications, including electronic devices, automotive systems, and medical devices. - Automotive Lighting : LEDs are used in automotive lighting applications, including headlights, taillights, and interior lighting. ### Advantages - Energy Efficiency : LEDs are highly energy-efficient and consume low power. - Long Lifespan : LEDs have a long lifespan and require less maintenance. - Design Flexibility : LEDs offer design flexibility and can be used in a variety of applications. - instant Lighting : LEDs provide instant lighting and do not require warm-up time. ### Disadvantages - Heat Sensitivity : LEDs are sensitive to heat and can be damaged by high temperatures. - "Voltage Sensitivity : LEDs are sensitive to voltage and require a specific voltage to operate. - color Temperature : LEDs can have different color temperatures, which can affect their performance and appearance. In conclusion, LEDs are highly efficient and versatile devices that offer a wide range of benefits and applications. Their energy efficiency, long lifespan, and design flexibility make them an attractive option for various lighting and display applications. Conclusion In conclusion, LEDs and solar cells are two impo rtant semi cond uctor devic es that have revolutionized the way we live and work. LEDs have transformed the lighting industry with their energy efficiency, long lifespan, and design flexibility, while solar cells have provided a sustainable and renewable source of energy. Both LEDs and solar cells have numerous benefits, including energy efficiency, reduced environmental impact, and increased reliability. As techn ology continues to advance, we can expe ct to see even more innovative applications of LEDs and solar cells, from smar t lighting syste ms to solar-powered homes and electric vehicles. Overall, LEDs and solar cells are playing a crucial role in shaping a more sustainable and energy-efficient future, and their impo rtanc e will only continue to grow in the years to come .

Formatting page ...

havangupta chat

Horizontal lines at:
Guest Horizontal lines at:
AutoRM Data:
Box geometries: