Grade 11
  1. Basic concepts of chemistry  1.1. Importance of Chemistry  1.2. Nature and scope of chemistry  1.3. laws of chemical combination  1.3.1. Law of conservation of mass  1.3.2. Law of definite proportions  1.3.3. Law of multiple proportions  1.3.4. Law of gaseous volume  1.3.5. Avogadro's Law  1.4. Dalton's atomic theory  1.5. Mole concept and molar mass  1.6. Percent composition  1.7. Empirical and molecular formula  1.8. Stoichiometry and Stoichiometric Calculations  1.9. Limiting reagent concept
  2. Structure of the atom  2.1. Discovery of the electron, proton, and neutron  2.2. Atomic Model  2.2.1. Thomson's model  2.2.2. Rutherford's model  2.2.3. Bohr's model  2.3. Quantum mechanical model of the atom  2.4. Dual nature of matter and radiation  2.5. Heisenberg's uncertainty principle  2.6. Quantum numbers  2.7. Atomic orbitals and their shapes  2.8. Electronic configuration of elements  2.9. Aufbau principle  2.10. Pauli's exclusion principle  2.11. Hund's maximum multiplicity rule  2.12. de Broglie's hypothesis  2.13. Photoelectric effect
  3. Classification of elements and periodicity in properties  3.1. Historical development of the periodic table  3.2. Modern Periodic Law and Periodic Table  3.3. Periodic trends in properties  3.3.1. Atomic and Ionic Radius  3.3.2. Ionization enthalpy  3.3.3. Electron gain enthalpy  3.3.4. Electronegativity  3.3.5. Valency  3.3.6. Metallic and Non-Metallic Properties  3.3.7. Oxidation states  3.4. Unusual Properties of the First Elements
  4. Chemical Bonding and Molecular Structure  4.1. Kossel–Lewis approach to chemical bonding  4.2. Ionic or electrovalent bond  4.3. Covalent bond and its features  4.4. Bond parameters  4.5. VSEPR Theory  4.6. Valence bond theory  4.7. Hybridization and its types  4.8. Molecular orbital theory  4.8.1. Bond order and stability  4.9. Hydrogen bonding
  5. States of matter  5.1. Intermolecular forces  5.2. Gas Laws  5.2.1. Boyle's law  5.2.2. Charles's Law  5.2.3. Avogadro's Law  5.2.4. Dalton's law of partial pressure  5.2.5. Graham's law of spread  5.3. Ideal Gas Equation and Applications  5.4. Real gases and deviations from ideal behaviour  5.5. Kinetic molecular theory of gases  5.6. Liquefaction of gases  5.7. Properties of Liquids  5.8. Surface tension and viscosity
  6. Thermodynamics  6.1. System and environment  6.2. Types of systems in thermodynamics  6.3. Types of procedures  6.4. First law of thermodynamics  6.5. Internal energy and enthalpy  6.6. Heat capacity and specific heat  6.7. Hess's law of constant heat summation  6.8. Bond dissociation enthalpy  6.9. Enthalpy of formation and combustion  6.10. Enthalpy of solution and neutralization  6.11. Spontaneity and the second law of thermodynamics  6.12. Gibbs free energy and its applications
  7. Balance  7.1. The concept of balance  7.2. Equilibrium constant and its applications  7.3. Le Chatelier's principle  7.4. Ionic equilibrium in solutions  7.5. Acid and Base Theory  7.5.1. Arrhenius concept  7.5.2. Bronsted-Lowry concept  7.5.3. Lewis concept  7.6. pH Scale and pOH  7.7. Common ion effect  7.8. Hydrolysis of salts  7.9. Buffer solutions and their mechanism of action  7.10. Solubility equilibrium of sparingly soluble salts
  8. Redox reactions  8.1. Oxidation and reduction concepts  8.2. Oxidation number and its applications  8.3. Redox reactions in terms of electron transfer  8.4. Balancing redox reactions (oxidation number and ion-electron methods)  8.5. Types of redox reactions  8.6. Electrochemical Cells and Redox Reactions
  9. Hydrogen  9.1. Position of Hydrogen in the Periodic Table  9.2. Isotopes of hydrogen  9.3. Preparation of Hydrogen  9.4. Properties of Hydrogen  9.5. Hydrides and their classification  9.6. Water and heavy water  9.7. Hydrogen peroxide and its properties  9.8. Uses of Hydrogen and Its Compounds
  10. S-block elements (alkali and alkaline earth metals)  10.1. Group 1 Elements - Properties and Trends  10.2. Group 2 Elements - Properties and Trends  10.3. Unusual properties of lithium and beryllium  10.4. Important compounds of sodium and their uses  10.5. Important Compounds of Magnesium and Calcium
  11. Some p-block elements  11.1. General Introduction to p-Block Elements  11.2. Group 13 Elements  11.2.1. Boron and its compounds  11.3. Group 14 Elements  11.3.1. Carbon and its allotropes  11.3.2. Important Compounds of Carbon and Silicon
  12. Organic Chemistry - Some Basic Principles and Techniques  12.1. Classification and Nomenclature of Organic Compounds  12.2. Structural representation of organic compounds  12.3. Classification of organic reactions  12.4. Electronic Effects in Organic Chemistry  12.4.1. Inductive effect  12.4.2. Resonance effect  12.4.3. Hyperconjugation  12.5. Reaction mechanism and intermediate species  12.6. Purification and qualitative analysis of organic compounds
  13. Hydrocarbons  13.1. Hydrocarbons  13.1.1. Preparation and Properties of Alkenes  13.2. alkene  13.2.1. Preparation and Properties of Alkenes  13.2.2. Electrophilic addition reactions  13.3. Alkynes  13.3.1. Preparation and Properties of Alkynes  13.4. Aromatic hydrocarbons  13.4.1. Structure and properties of benzene  13.4.2. Electrophilic substitution reactions of benzene
  14. Environmental Chemistry  14.1. Environmental Pollution  14.2. Atmospheric pollution and the greenhouse effect  14.3. Water pollution and treatment methods  14.4. Soil pollution and its effects  14.5. Industrial waste and its treatment  14.6. Strategies for pollution control

Grade 11 → Structure of the atom ↓


Photoelectric effect


The photoelectric effect is a fundamental concept in the study of atomic physics and quantum mechanics. It revolves around the emission of electrons from the surface of a substance, usually metal, when it absorbs electromagnetic radiation such as light. This phenomenon is important because it challenges classical physics and supports the quantum theory of light. In this detailed explanation, we will discuss in depth the photoelectric effect, its discovery, the experimental evidence supporting it, and its implications on modern science.

Discovery of the photoelectric effect

The photoelectric effect was first observed by Heinrich Hertz in 1887, but a theoretical explanation was provided by Albert Einstein in 1905. Hertz observed that when ultraviolet light was shone on a metal electrode, the electrical properties of the electrode changed, indicating that electrons were being emitted. A few years later, Wilhelm Hallwachs and Philipp Lenard performed experiments that further confirmed Hertz's observations.

Classical physics versus the photoelectric effect

According to classical physics, light is considered a wave. When it strikes a metal surface, it is expected that the energy will spread evenly across the surface, and after enough time, the electrons will get enough energy to get ejected. However, the photoelectric effect does not behave according to these predictions. Here are the key observations:

  • When light struck the surface, electrons were emitted almost instantaneously, whereas a delay in energy absorption was expected.
  • The kinetic energy of the emitted electrons depended on the frequency of the light, not its intensity.
  • There is a limiting frequency below which no electrons are emitted regardless of the light intensity.
  • The number of electrons emitted was proportional to the light intensity, assuming the frequency was above a threshold.

Einstein's explanation

Albert Einstein revolutionized the understanding of this effect by introducing the concept of light quanta (now known as photons). According to Einstein, light is composed of discrete packets of energy. Each photon has energy, which is given as:

E = hν

where E is the energy of the photon, h is the Planck constant (about 6.626 x 10^-34 Js ), and ν (nu) is the frequency of the electromagnetic wave.

When a photon strikes a metal surface, its energy is transferred to an electron. If the energy of the photon is greater than the work function (φ) of the metal, the electron is emitted. The kinetic energy (KE) of the emitted electron can be calculated as:

KE = hν - φ

Experimental evidence

To understand the photoelectric effect experimentally, consider a vacuum tube in which a light source illuminates a metal plate (emitter). The emitted electrons are collected by another plate (collector), forming a current. The experiments carried out showed:

  • Emission of electrons: The electrons are emitted immediately after the light falls, there is no delay in this.
  • Kinetics and frequency: The kinetic energy of the electrons depends directly on the frequency of light, not on its intensity.
  • Threshold frequency: If the frequency of light is less than a certain threshold frequency, no photoelectrons are emitted, no matter how intense the light is.
  • Photoelectric current: The current increases with increase in light intensity provided the frequency is above the limit.

Visual example

Look at the following diagram which shows the photoelectric effect:

Metal Electron Emission E=hv

The orange rectangle shows the metal surface, while the blue circle shows the collector. When light (green lines) strikes the metal, electrons (indicated by arrows) are emitted, and the energy equations are satisfied, confirming the photoelectric effect.

Applications of photoelectric effect

The photoelectric effect is not just a theoretical concept; it has practical applications in many areas:

  • Photoelectric cells: This effect is used in devices such as photoelectric cells (solar panels), which convert light energy into electrical energy.
  • Light meters: Cameras rely on light meters to adjust exposure time by analyzing the number of emitted photons that interact with a surface.
  • Integrated circuit manufacturing: Understanding electron emission can help develop integrated circuits and improve semiconductor technology.

Importance of photoelectric effect

The photoelectric effect played a key role in the development of quantum mechanics. By proving that light can behave as particles as well as waves, it led to the realization that matter exhibits the same dual properties. Furthermore, understanding this phenomenon has been crucial in enhancing various technologies, including photovoltaics and quantum computing.

Einstein and the Nobel Prize

Albert Einstein was awarded the Nobel Prize in Physics in 1921, primarily for his explanation of the photoelectric effect rather than for his theory of relativity. The award underlines the impact and importance of his contributions to our understanding of quantum physics.

Conclusion

The photoelectric effect is the basis of quantum mechanics that challenged classical physics and expanded our understanding of the nature of light. Its implications reach beyond basic physics to practical applications and advanced technologies, affecting everything from energy production to the development of modern electronics. The phenomenon exemplifies the fascinating behavior of particles at the quantum level, and its study remains a vital part of scientific progress.


Grade 11 → 2.13


U
username
0%
completed in Grade 11

← Prev (2.12)
de Broglie's hypothesis
Next (3) →
Classification of elements and periodicity in properties

Comments 



Photoelectric effect

https://www.chemistryelite.com/g11/2.13?ceal=en