Grade 9
  1. Mechanics  1.1. Motion  1.1.1. Types of motion  1.1.2. Distance and displacement  1.1.3. Speed and Velocity  1.1.4. Acceleration  1.1.5. Graphical representation of motion  1.1.6. Equations of motion  1.1.7. Uniform and non-uniform motion  1.1.8. Free fall and acceleration due to gravity  1.1.9. Relative speed  1.1.10. Circular motion  1.2. Laws of force and motion  1.2.1. The concept of force  1.2.2. newton's first law of motion  1.2.3. Newton's second law of motion  1.2.4. Newton's third law of motion  1.2.5. Inertia and types of inertia  1.2.6. Motion  1.2.7. Conservation of momentum  1.2.8. Application of Newton's laws in daily life  1.2.9. Types of Forces (Contact and Non-Contact)  1.2.10. Friction and its effects  1.3. Gravitational force  1.3.1. Newton's law of universal gravitation  1.3.2. Importance of Gravitational Force  1.3.3. Acceleration due to gravity  1.3.4. Free fall and weightlessness  1.3.5. Mass and weight  1.3.6. Variation of g with height and depth  1.3.7. Kepler's laws of planetary motion  1.3.8. Satellites and their orbits  1.4. Work, Energy and Power  1.4.1. Concept of work  1.4.2. Positive and negative actions  1.4.3. Work done by constant and variable force  1.4.4. Energy and its forms  1.4.5. Kinetic energy and potential energy  1.4.6. Law of conservation of energy  1.4.8. Commercial unit of energy  1.4.9. Work–energy theorem  1.5. Simple machines  1.5.1. Types of simple machines  1.5.2. Mechanical advantage  1.5.3. Machine efficiency  1.5.4. Levers and their types  1.5.5. Pulleys and Inclined Planes  1.5.6. Gears and their uses
  2. Properties of matter  2.1. States of matter  2.1.1. Solids, liquids and gases  2.1.2. Properties of different states of matter  2.1.3. Change in state of matter  2.1.4. Plasma and Bose–Einstein condensate  2.2. Density and pressure  2.2.1. Concept of density and relative density  2.2.2. Pressure in solids, liquids and gases  2.2.3. Pascal's law and its applications  2.2.4. Atmospheric pressure and its variations  2.2.5. Surface tension and capillarity  2.3. Buoyancy and Archimedes' principle  2.3.1. Buoyant force  2.3.2. Archimedes principle  2.3.3. Applications of Archimedes' Principle  2.3.4. floating and sinking objects  2.3.5. Theory of Flotation and Archimedes' Principle
  3. Heat and Thermodynamics  3.1. Temperature and heat  3.1.1. Concept of heat and temperature  3.1.2. Temperature measurement  3.1.3. Temperature scales  3.2. Heat transfer  3.2.1. Conduction of heat  3.2.2. Convection of heat  3.2.3. heat radiation  3.2.4. Applications of heat transfer  3.2.5. Thermal conductivity  3.3. Thermal expansion  3.3.1. Expansion of solids, liquids and gases  3.3.2. Abnormal expansion of water  3.3.3. Applications of Thermal Expansion  3.4. Specific heat capacity and latent heat  3.4.1. Concept of specific heat capacity  3.4.2. Measurement and applications of specific heat  3.4.3. Latent heat of fusion and vaporization  3.4.4. Heat Engines and Efficiency
  4. Waves and sound  4.1. Waves and their types  4.1.1. Mechanical and electromagnetic waves  4.1.2. Longitudinal and Transverse Waves  4.1.3. Properties of Waves  4.1.4. Wavelength, frequency and speed of the wave  4.1.5. Superimposition of waves  4.2. Sound waves  4.2.1. Nature and transmission of sound  4.2.2. Speed of sound in different mediums  4.2.3. Reflection of sound and echo  4.2.4. Sonar and ultrasound  4.2.5. Resonance and pulsation  4.3. Sound characteristics  4.3.1. Intensity, loudness and quality of sound  4.3.2. Doppler effect in sound
  5. Lighting and Optics  5.1. Reflection of light  5.1.1. Laws of reflection  5.1.2. Reflection from a plane mirror  5.1.3. Reflection from a spherical mirror  5.1.4. Image formation by concave and convex mirrors  5.1.5. Applications of Reflection  5.2. Refraction of light  5.2.1. Laws of refraction  5.2.2. Refractive index  5.2.3. Refraction through a glass slab  5.2.4. Refraction in water and air  5.2.5. Lenses and their types  5.2.6. Image formation by convex and concave lenses  5.2.7. Total internal reflection and its applications  5.3. Dispersion and scattering of light  5.3.1. Spectrum of white light  5.3.2. Prisms and Dispersion  5.3.3. Tyndall effect and blue sky
  6. Electricity and Magnetism  6.1. Electric charge and static electricity  6.1.1. The concept of electric charge  6.1.2. Charging by friction, contact and induction  6.1.3. Electroscope and its working  6.2. Current Electricity  6.2.1. The concept of electric current  6.2.2. Ohm's Law and Resistance  6.2.3. Factors affecting resistance  6.2.4. Series and Parallel Circuits  6.2.5. Heating effect of electric current  6.2.6. Electric power and energy  6.3. Magnetism  6.3.1. Natural and artificial magnets  6.3.2. Properties of magnets  6.3.3. Earth's magnetism  6.3.4. Magnetic field and field lines  6.3.5. Electromagnets and their applications
  7. Modern Physics  7.1. structure of the atom  7.1.1. Atomic Structure and Subatomic Particles  7.1.2. Electrons, Protons, and Neutrons  7.1.3. Rutherford and Bohr model  7.2. Radioactivity  7.2.1. Types of radioactive emissions  7.2.2. Half-life and radioactive decay  7.2.3. Uses and Hazards of Radioactivity
  8. Space science and astronomy  8.1. The universe and its components  8.1.1. Stars and galaxies  8.1.2. Planets and Solar System  8.2. Satellites  8.2.1. Natural and artificial satellites  8.2.2. Use of satellites

Grade 9 → Lighting and Optics → Refraction of light ↓


Refraction through a glass slab


Refraction is a fascinating phenomenon that occurs when light passes from one medium to another. A common example of refraction is when light passes through a glass slab. In this lesson, we will explore the concept of refraction through a glass slab in detail using simple language and examples that make it easier to understand.

Understanding refraction

Before we dive into refraction through a glass slab, let's first understand what refraction is. Refraction is the bending of light when it passes from one medium to another. This happens because light travels at different speeds in different mediums. When light enters a medium at an angle, its speed changes, which changes its direction.

Snell's law

The bending of light during refraction is governed by Snell's law. Snell's law relates the angle of incidence (i) and the angle of refraction (r) to the refractive index of the two media involved. Mathematically, Snell's law can be expressed as:

n1 * sin(i) = n2 * sin(r)

Where:

  • n1 is the refractive index of the first medium
  • n2 is the refractive index of the second medium
  • i is the angle of incidence
  • r is the angle of refraction

Visual example: light entering a slab of glass

Consider a ray of light traveling from air to a glass slab. The refractive index of air is lower than that of glass. As the light strikes the surface of the glass slab, it bends toward the normal. Here is a visualization:

Air glass General

Glass slab experiment

Let's do a simple thought experiment to understand the behaviour of light through a glass slab. Imagine a rectangular glass slab with parallel surfaces. When a light ray enters the glass slab at an angle, it undergoes refraction at the air-glass interface and bends towards the normal.

After passing through the glass, the light ray reaches the second surface (the glass-air interface). Again, it bends but this time away from the normal, emerging out into the air. Due to the parallel nature of the surfaces, the emerging ray is parallel to the incident ray, although it has been displaced laterally.

Calculating refraction

Let's calculate the angle of incidence and refraction using Snell's law. Suppose the refractive index of air is about 1.00, and the refractive index of glass is about 1.50. If the angle of incidence is 30 degrees, we can use Snell's law to find the angle of refraction:

n1 * sin(i) = n2 * sin(r)
1.00 * sin(30 degrees) = 1.50 * sin(r)
sin(30 degrees) = 0.5
1.00 * 0.5 = 1.50 * sin(r)
sin(r) = (1.00 * 0.5) / 1.50
sin(r) = 0.3333

Using a calculator, the angle r can be found by the inverse sine of 0.3333, which is approximately equal to 19.47 degrees. Thus, when light enters the glass slab, it bends less in the denser medium.

Visualization of refraction in a glass slab

Now that the calculations are complete, let's visualize the full path of a light beam passing through the glass strip into the air:

incident ray Inside the glass rising ray

Lateral displacement

As we saw in the scene, the incident ray and the emergent ray are parallel but not on the same path. This separation between the incident and emergent ray is called lateral displacement. The amount of lateral displacement depends on the thickness of the glass slab, the angle of incidence and the refractive index of the glass.

Applications of refraction through a glass slab

Refraction is not just a theoretical concept. It has many practical applications, especially in optics. Here are some everyday examples:

  • Optical instruments: Glass slabs and lenses are used to direct and focus light to form clear images in instruments such as cameras, microscopes, and telescopes.
  • Glasses: Corrective lenses in eyeglasses use the principles of refraction to adjust the focal point of light entering the eye.
  • Fiber optics: Refraction is essential in the functioning of fiber optic cables, which transmit light signals over long distances with minimal loss.

Conclusion

Refraction through a glass slab is a fundamental concept in optics, which shows how light interacts with different media. Understanding this process helps us understand how optical instruments work and affects many technological areas. Through simple experiments and calculations, we can appreciate the accuracy and predictability of the behavior of light.


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Refraction through a glass slab

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