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 ↓


Reflection of light


Reflection of light is a fundamental concept in the field of optics, involving the return of light rays when they hit a surface. This process is something we see everyday, whether it is the reflection of our face in a mirror or the way sunlight creates glare on a lake. Understanding how light reflects will help us understand how we see objects and how mirrors and other reflective surfaces work.

The basics of thinking

When light strikes a surface, it can be absorbed, transmitted, or reflected. Reflection occurs when light strikes a surface. The angle at which light strikes a surface is called the angle of incidence and the angle at which it reflects is called the angle of reflection. Both angles are measured from the normal line, which is an imaginary line perpendicular to the surface at the point of incidence.

Generalincident rayReflected rayangle of incidenceangle of reflection

Laws of reflection

Reflection of light follows two major laws:

  1. The angle of incidence is equal to the angle of reflection. This means that if a ray of light falls on a surface at an angle of 30 degrees to the normal, it will reflect at the same 30 degree angle on the other side of the normal.
  2. The incident ray, the reflected ray and the normal all lie in the same plane. This means that reflection takes place in a plane space and there is no distortion in the direction of the reflected ray.
incidence_angle = reflection_angle

These rules are the same in all types of reflection, whether it is from a smooth surface like a mirror or from a rough surface like a wall.

Types of reflection

There are two primary types of reflection:

1. Specular reflection

Specular reflection occurs when light reflects off a smooth, shiny surface, such as a mirror or a still body of water. In this type of reflection, the reflected rays remain parallel to each other. This convergent reflection is what allows us to see clear images in mirrors.

Incident raysReflected rays

2. Diffuse reflection

Diffuse reflection occurs when light reflects from a rough surface. Here, light rays scatter in many different directions because the irregularities in the surface cause variations in the angles of incidence. Diffuse reflection is the reason we are able to see objects that are not shiny, as the scattered light reflects into our eyes at different angles.

Incident raysReflected rays

Real-life examples of reflection

Understanding reflection through real-life examples can help make the concept clear:

  • Mirrors: Mirrors are designed with a smooth surface to maximize reflection, allowing us to see clear images of objects, including ourselves.
  • Shiny surfaces: Many metals and polished surfaces use specular reflection to create a shiny appearance.
  • White walls: Walls that appear white often have a rough surface, which causes diffuse reflection, scattering light evenly and making the walls appear shiny from different angles.
  • Road signs: Road signs often use materials that enhance diffuse reflectance to make them visible in low light conditions by scattering light from vehicle headlights.

Applications of reflection

Reflection has wide applications in various fields, some of which are as follows:

1. Optical instruments

Reflection principles are important in the design of optical instruments such as telescopes and microscopes. Mirrors are used to focus and direct light to increase the clarity and detail of the image.

2. Periscope

Periscopes rely on mirrors placed at angles, allowing the viewer to see over or around obstacles, and use specular reflection to transmit images from one end to the other.

3. Rear-view mirror

In vehicles, rear-view mirrors are designed to provide drivers with a view of vehicles and objects behind them, using the principles of specular reflection.

Mathematical representation

The process of reflection can also be described mathematically. If we consider light to be traveling in straight lines, we can use trigonometry to describe how light behaves when it reflects off a surface.

Example

If a ray of light strikes a flat surface at an angle of 30 degrees to the normal, we can use the law of reflection to determine that the angle of reflection will also be 30 degrees. If the direction of the incident ray is given by the vector (x, y, z), then the direction of the reflected ray can be found using vector reflection formulas.

R = I - 2 * (I . N) * N

Where:

  • I is the incident ray direction vector.
  • N is the normal vector.
  • R is the reflected ray direction vector.
  • (I . N) is the dot product of vectors I and N

Conclusion

The reflection of light is a fundamental aspect of optics, providing vital information about how we see the world around us. Understanding reflection enables us to design effective optical devices, improve safety through clear signs and mirrors, and appreciate the functionality of everyday objects that rely on reflective principles. By recognizing the simple rules governing reflection and observing its effects in nature and technology, we gain a more profound understanding of the ways in which light interacts with the environment.


Grade 9 → 5.1


U
username
0%
completed in Grade 9

← Prev (5)
Lighting and Optics
Next (5.1.1) →
Laws of reflection

Comments 



Reflection of light

https://www.physicsflow.com/g9/5.1?pfal=en