Topics
Electric Charges and Fields
- Electric Charge
- Conductors and Insulators
- Basic Properties of Electric Charge
- Coulomb’s Law
- Forces between Multiple Charges
- Electric Field
- Electric Field Due to a System of Charges
- Physical Significance of Electric Field
- Electric Field Lines
- Electric Flux
- Electric Dipole
- Dipole in a Uniform External Field
- Continuous Charge Distribution
- Gauss’s Law
- Application of Gauss' Law
Electrostatics
Current Electricity
Electrostatic Potential and Capacitance
- Electric Potential and Potential Energy
- Electrostatic Potential
- Electric Potential Due to a Point Charge
- Potential Due to an Electric Dipole
- Potential due to a System of Charges
- Equipotential Surfaces
- Relation Between Electric Field and Electrostatic Potential
- Potential Energy of a System of Charges
- Potential Energy of a Single Charge
- Potential Energy of a System of Two Charges in an External Field
- Potential Energy of a Dipole in an External Field
- Electrostatics of Conductors
- Dielectrics and Polarisation
- Capacitors and Capacitance
- The Parallel Plate Capacitor
- Effect of Dielectric on Capacitance
- Combination of Capacitors
- Energy Stored in a Charged Capacitor
Magnetic Effects of Current and Magnetism
Current Electricity
- Electric Current
- Electric Currents in Conductors
- Ohm's Law
- Drift of Electrons and the Origin of Resistivity
- Mobility of Electrons
- Limitations of Ohm’s Law
- Resistivity of Various Materials
- Temperature Dependence of Resistivity
- Electrical Energy and Power in Conductors
- Cells, EMF, and Internal Resistance
- Cells in Series and in Parallel
- Kirchhoff’s Laws
- Wheatstone Bridge
Electromagnetic Induction and Alternating Currents
Moving Charges and Magnetism
- Electromagnetism
- Magnetic force
- Motion in a Magnetic Field
- Magnetic Field Due to a Current-carrying Conductor: Biot-savart's Law
- Applications of Biot-Savart's Law > Magnetic Field at the Axis of a Circular Current-carrying Loop
- Ampere’s Circuital Law
- Solenoid
- Force Between Two Parallel Currents (Ampere’s Law)
- Torque on a Rectangular Current Loop in a Uniform Magnetic Field
- Circular Current Loop as a Magnetic Dipole
- Moving Coil Galvanometer
- Kirchhoff’s Laws
Electromagnetic Waves
Magnetism and Matter
Electromagnetic Induction
Optics
Dual Nature of Radiation and Matter
Alternating Current
Atoms and Nuclei
Electromagnetic Waves
Electronic Devices
Ray Optics and Optical Instruments
- Ray Optics Or Geometrical Optics
- Reflection of Light by Spherical Mirrors
- Sign Convention for Reflection by Spherical Mirrors
- Focal Length of Spherical Mirrors
- Mirror Equation of Spherical Mirrors
- Refraction of Light
- Total Internal Reflection
- Applications of Total Internal Reflection
- Refraction at a Spherical Surfaces
- Refraction by a Lens
- Power of a Lens
- Combined Focal Length of Two Thin Lenses in Contact
- Refraction of Light Through a Prism
- Optical Instruments
- Microscope and it’s types
- Telescope
Wave Optics
- Concept of Wave Optics
- Huygens Principle
- Refraction of a Plane Wave
- Refraction at a Rarer Medium
- Reflection of a Plane Wave by a Plane Surface
- Coherent and Incoherent Addition of Waves
- Interference of Light Waves and Young’s Experiment
- Diffraction of Light
- The Single Slit
- Seeing the Single Slit Diffraction Pattern
- Polarisation of Light
Communication Systems
The Special Theory of Relativity
Dual Nature of Radiation and Matter
- Understanding Dual Nature of Radiation and Matter
- Electron Emission
- Photoelectric Effect - Hertz’s Observations
- Photoelectric Effect - Hallwachs’ and Lenard’s Observations
- Experimental Study of Photoelectric Effect
- Effects of Intensity and Frequency on Photocurrent
- Photoelectric Effect and Wave Theory of Light
- Einstein’s Photoelectric Equation: Energy Quantum of Radiation
- Particle Nature of Light: The Photon
- Wave Nature of Matter
Atoms
Nuclei
Semiconductor Electronics - Materials, Devices and Simple Circuits
Communication Systems
- Detection of Amplitude Modulated Wave
- Production of Amplitude Modulated Wave
- Basic Terminology Used in Electronic Communication Systems
- Sinusoidal Waves
- Modulation and Its Necessity
- Amplitude Modulation (AM)
- Need for Modulation and Demodulation
- Satellite Communication
- Propagation of EM Waves
- Bandwidth of Transmission Medium
- Bandwidth of Signals
The Special Theory of Relativity
- The Special Theory of Relativity
- The Principle of Relativity
- Maxwell'S Laws
- Kinematical Consequences
- Dynamics at Large Velocity
- Energy and Momentum
- The Ultimate Speed
- Twin Paradox
Estimated time: 8 minutes
CBSE: Class 12
Introduction
- Metals contain a large number of free electrons that are responsible for electrical conduction.
- These electrons move freely inside the metal, but they are not completely free to leave the surface.
- At the surface of the metal, attractive forces due to positive ions pull the electrons inward and prevent them from escaping under ordinary conditions.
Student Analogy
- Think of the metal surface as a boundary wall.
- A free electron may move inside the playground, but it needs a minimum push to jump over the wall and come out.
- That minimum push is the work function.
CBSE: Class 12
Definition: Electron Emission
The phenomenon of emission of electrons from the metal surface is called "Electron Emission".
CBSE: Class 12
Definition: Work Function
The minimum energy required by an electron to escape from the surface of a metal is called the work function (ϕ0) of that metal.
Unit: electron volt (eV).
CBSE: Class 12
Definition: Electron Volt (eV)
An electron volt is the energy gained by an electron when it is accelerated through a potential difference of 1 volt.
1 eV = 1.602 × 10−19J
CBSE: Class 12
Mechanism of Electron Emission
Electron emission occurs when energy is supplied to a metal electron so that it can overcome the surface attraction and escape from the metal.
Flow Sequence
- Metal contains free electrons.
- Surface positive ions hold these electrons inside the metal.
- External energy is supplied to an electron.
- If supplied energy ≥ ϕ0, the electron escapes.
- The process is called electron emission.
CBSE: Class 12
Methods of Electron Emission
According to the source material, electrons can be emitted from a metal surface in three main ways.
- Thermionic Emission: When a metal is heated, thermal energy is supplied to its electrons.
If some electrons gain enough energy to overcome the work function, they escape from the surface.
Example: Emission of electrons from a heated filament in vacuum tubes.
Memory aid: Heat gives energy to electrons. - Field Emission: When a very strong electric field is applied across the metal surface, electrons can be pulled out of the metal.
This requires a very high field of the order of 108 V m−1.
Example: Sharp metal tips in special electronic devices.
Memory aid: Field pulls electrons out. - Photoelectric Emission: When light of suitable frequency falls on a metal surface, electrons may be emitted. This process is called photoelectric emission.
Example: Photoelectric cells and light sensors.
Memory aid: Light knocks electrons out.
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