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 Element, Biot-savart Law
- Magnetic Field on 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
Maharashtra State Board: Class 11
CISCE: Class 12
Introduction
Total Internal Reflection is the phenomenon in which a ray of light is completely reflected back into the denser medium when it travels from a denser medium to a rarer medium and the angle of incidence becomes greater than the critical angle.
Core Idea
As the angle of incidence increases for light going from a denser medium to a rarer medium, the angle of refraction also increases. At one particular angle of incidence, the angle of refraction becomes 90 degrees; this angle of incidence is called the critical angle. If the angle of incidence becomes greater than the critical angle, refraction stops, and the ray is reflected completely inside the denser medium.
Maharashtra State Board: Class 11
CISCE: Class 12
Definition: Total Internal Reflection
Total internal reflection is the complete reflection of light back into an optically denser medium when light travels from a denser medium to a rarer medium and the angle of incidence exceeds the critical angle.
Maharashtra State Board: Class 11
CISCE: Class 12
Definition: Critical Angle
The critical angle is the angle of incidence in the denser medium for which the angle of refraction in the rarer medium is 90 degrees.
Formula: Critical Angle
For light travelling from medium 1 to medium 2, where medium 1 is denser than medium 2:
where:
- C = critical angle
- n1 = refractive index of the denser medium
- n2 = refractive index of rarer medium
For a denser medium to air:
sin C = \[\frac {1}{μ}\]
where μ is the refractive index of the denser medium with respect to air.
Maharashtra State Board: Class 11
CISCE: Class 12
Conditions for Total Internal Reflection
Total internal reflection takes place only when both of the following conditions are satisfied:
- Light must travel from an optically denser medium to an optically rarer medium.
- The angle of incidence in the denser medium must be greater than the critical angle for the two media.
If even one condition is missing, total internal reflection will not occur.
Mechanism of Total Internal Reflection
| Angle of Incidence | Behaviour of Light | Result |
|---|---|---|
| Less than the critical angle | Light refracts into a rarer medium | Refraction occurs |
| Equal to the critical angle | The refracted ray travels along the interface | Angle of refraction = 90° |
| Greater than the critical angle | Light returns fully into a denser medium | Total internal reflection |
Cause:
Total internal reflection occurs because a refracted ray can exist only up to the condition where the refracted angle becomes 90°. Beyond that limit, light cannot pass into the rarer medium as a refracted ray, so it is reflected back into the denser medium.
Critical Angles in Air
| Substance medium | Refractive index | Critical angle |
|---|---|---|
| Water | 1.33 | 48.75 |
| Crown glass | 1.52 | 41.14 |
| Dense flint glass | 1.62 | 37.31 |
| Diamond | 2.42 | 24.41 |
Real-Life Examples
- Sparkle of Diamond: A diamond has a high refractive index and a small critical angle, so light entering it undergoes repeated internal reflections.byjus+1 This produces its bright sparkling appearance.
- Mirage: Mirage formation is explained using refraction and total internal reflection in layers of air at different temperatures.
