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 from a plane mirror


Reflection of light is a fundamental concept in the study of optics and physics. Light can travel straight, but when it hits an object, it changes its path. When this object is a mirror, the light reflects. This is what we call reflection of light. Let's focus on how light reflects from plane mirrors, which are flat, smooth mirrors.

Fundamentals of thinking

Reflection occurs when light hits a surface and reflects back. Here are some key terms and concepts:

  • Incident ray: The light ray that falls on the surface.
  • Reflected ray: The ray of light that bounces back after striking a surface.
  • Normal: An imaginary line perpendicular to the surface at the point of incidence.
  • Angle of incidence (i): The angle between the incident ray and the normal.
  • Angle of reflection (r): The angle between the reflected ray and the normal.

Laws of reflection

There are two primary laws of reflection that apply to plane mirrors:

  1. The angle of incidence is equal to the angle of reflection.
  2. The incident ray, the reflected ray and the normal all lie in the same plane.

This means that if a ray of light falls on the mirror at an angle of 30° to the normal, then it will reflect on the other side of the normal line at the same angle of 30°.

    Angle of incidence (i) = Angle of reflection (r)

Visual representation

Below is a simple visual illustration:

General Incident ray Reflected ray

Characteristics of images formed by a plane mirror

The images formed by plane mirrors have distinctive features:

  • Virtual image: The image cannot be projected on a screen, as it appears to be located behind the mirror.
  • Upright: The image maintains the same orientation as the object.
  • Same size: The image is the same size as the object.
  • Laterally inverted (left-right reversed): The image appears reversed from left to right.
  • Equal distance: The image appears as far behind the mirror as the object is in front of it. This can be represented mathematically as follows:
    •             Distance of object (d_o) = Distance of image (d_i)

Text example

Consider standing in front of a plane mirror at a distance of 1 m:

  • You will see your image 1 meter behind the mirror.
  • If you are holding a sign that says "Hello" in your right hand, the image will show you holding that sign in your left hand.
  • The height of the image will be the same as your height.

Applications of plane mirrors

Plane mirrors are widely used due to their simplicity and efficiency:

  • Mirrors in homes: Used for daily purposes such as beauty and interior designing.
  • Optical instruments: Used in instruments such as periscopes, telescopes, and microscopes for reflection.
  • Decoration and architecture: Used in buildings and art installations to create the illusion of space and enhance aesthetics.

Understanding reflection symmetry

When studying plane mirrors, it is important to understand reflectional symmetry:

If an object is symmetrical, you can draw a line through its middle, and each side will be identical. In the context of mirrors, this line represents the surface of the mirror.

Visual example of symmetry

Object Image

Practical experiment: Creating an image

To understand how reflection works with plane mirrors, you can do this simple experiment:

Required materials:

  • A small plane mirror
  • A piece of plain paper
  • A pencil
  • A protractor
  • A ruler

Phase:

  1. Place the mirror straight on the paper.
  2. Mark a point (A) on one side of the mirror as an image.
  3. Draw a straight line from point A to the mirror (it reflects the incident ray).
  4. Use the protractor to draw the normal at the point where the incident ray touches the mirror.
  5. Measure the angle of incidence using a protractor.
  6. Draw the reflected ray such that the angle of incidence is equal to the angle of reflection.
  7. Extend both the incident and reflected rays behind the mirror. The point of intersection gives you the image (A').

By carrying out this experiment, you will see how the rays of light reflect from the mirror and form an image.

Conclusion

Understanding reflection from plane mirrors is an integral part of learning the behavior of light. By mastering these concepts, you are equipped to understand more complex optical phenomena. Reflection principles are foundational and apply in a variety of technical and scientific fields.

Remember the basic principles: the angle of incidence is equal to the angle of reflection, and the image formed by a plane mirror is virtual, erect, laterally inverted, and the same size and distance from the mirror as the object. These fundamental concepts are important when studying light and optics.


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Reflection from a plane mirror

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