Grade 10
  1. Mechanics  1.1. Dynamics  1.1.1. Motion in one dimension  1.1.2. Motion in two dimensions  1.1.3. Displacement and Distance  1.1.4. Speed and Velocity  1.1.5. Acceleration  1.1.6. Graphical representation of motion  1.1.7. Equations of motion  1.1.8. Free fall and acceleration due to gravity  1.1.9. Projectile motion  1.1.10. Relative speed  1.2. Dynamics  1.2.1. Newton's Laws of Motion  1.2.2. Inertia and mass  1.2.3. Force and its types  1.2.4. action and reaction force  1.2.5. Friction and its effects  1.2.6. Coefficient of friction  1.2.7. Circular motion  1.2.8. Centripetal force and centripetal acceleration  1.2.9. Momentum and Impulse  1.2.10. Conservation of momentum  1.2.11. Newton's third law and applications  1.3. Work, Energy and Power  1.3.1. Work done by the force  1.3.2. Work–energy theorem  1.3.3. Kinetic energy  1.3.4. Potential energy  1.3.5. Mechanical energy  1.3.6. Energy Conservation  1.3.7. Power and efficiency  1.3.8. Renewable and non-renewable energy sources  1.4. Gravitational force  1.4.1. Newton's law of universal gravitation  1.4.2. Gravitational field and field strength  1.4.3. Acceleration due to gravity on different planets  1.4.4. Kepler's laws of planetary motion  1.4.5. Orbits and satellites  1.4.6. Weight and apparent weight  1.4.7. Gravitational potential energy
  2. Properties of matter  2.1. States of matter  2.1.1. Solid, liquid and gas  2.1.2. Molecular structure of matter  2.1.3. Intermolecular forces  2.1.4. Plasma and Bose–Einstein condensate  2.2. Pressure  2.2.1. Definition of Pressure  2.2.2. Pressure in liquids  2.2.3. Atmospheric pressure  2.2.4. Pascal's principle  2.2.5. Archimedes' Principle and Buoyancy  2.2.6. Surface tension and capillarity  2.3. Elasticity  2.3.1. Hooke's law  2.3.2. Stress and strain  2.3.3. Elastic Limit and Modulus of Elasticity  2.3.4. Applications of Elasticity
  3. Thermal physics  3.1. heat and temperature  3.1.1. Difference Between Heat and Temperature  3.1.2. Temperature scale  3.1.3. Thermal expansion  3.1.4. Thermal equilibrium  3.2. Heat transfer  3.2.1. Conductivity  3.2.2. Convection  3.2.3. Radiation  3.2.4. Insulation and its applications  3.3. Thermal properties of matter  3.3.1. Specific heat capacity  3.3.2. Latent heat and phase change  3.3.3. Boiling and Melting Point  3.3.4. Heat engines and refrigeration  3.4. Laws of Thermodynamics  3.4.1. Zeroth law of thermodynamics  3.4.2. First law of thermodynamics  3.4.3. Second law of thermodynamics  3.4.4. Carnot cycle
  4. Waves and optics  4.1. Nature and properties of waves  4.1.1. Types of waves in nature and properties of waves  4.1.2. Transverse and longitudinal waves  4.1.3. Wave parameters  4.1.4. Reflection and refraction of waves  4.1.5. Superposition and Interference  4.1.6. Standing Waves and Resonance  4.1.7. Doppler effect  4.2. Sound waves  4.2.1. Characteristics of sound waves  4.2.2. Speed of sound in different mediums  4.2.3. Applications of sound waves  4.2.4. Ultrasound and its uses  4.3. Light Waves and Optics  4.3.1. Nature of light  4.3.2. Reflection of light  4.3.3. Laws of reflection  4.3.4. Mirrors and Image Formation  4.3.5. Refraction of light  4.3.6. Snell's Law  4.3.7. Lenses and Image Formation  4.3.8. Total internal reflection and critical angle  4.3.9. Optical fibre  4.4. Optical Instruments  4.4.1. Microscope  4.4.2. Telescope  4.4.3. Human eye and vision defects  4.4.4. Camera and its working principle
  5. Electricity and Magnetism  5.1. Electrostatics  5.1.1. Electric charge and its properties  5.1.2. Conductors and Insulators  5.1.3. Coulomb's law  5.1.4. Electric field and field lines  5.1.5. Electric potential and potential difference  5.1.6. Capacitors and Capacitance  5.2. Current Electricity  5.2.1. Electric current and its measurement  5.2.2. Ohm's law  5.2.3. Resistance and resistivity  5.2.4. Series and Parallel Circuits  5.2.5. Electric power and energy  5.2.6. Kirchhoff's Laws  5.3. Magnetism and Electromagnetism  5.3.1. Magnetic field and field lines  5.3.2. Magnetic effects of electric current  5.3.3. Electromagnetic induction  5.3.4. Faraday's laws of electromagnetic induction  5.3.5. Transformers and Applications  5.3.6. AC and DC current
  6. Modern Physics  6.1. Nuclear physics  6.1.1. Structure of the atom  6.1.2. Bohr's atomic model  6.1.3. Electron Energy Levels  6.1.4. X-rays and applications  6.2. Radioactivity  6.2.1. Types of radiation  6.2.2. Half-life and radioactive decay  6.2.3. Nuclear reactions and applications  6.2.4. Fission and Fusion  6.3. Quantum physics  6.3.1. Wave–particle duality  6.3.2. Photoelectric effect  6.3.3. Energy quantization  6.3.4. Heisenberg's uncertainty principle
  7. Electronics and Communication  7.1. Semiconductors  7.1.1. Conductors, Insulators and Semiconductors  7.1.2. Diodes and their applications  7.1.3. Transistors and Logic Gates  7.1.4. LEDs and photodiodes  7.2. Communication Systems  7.2.1. Basics of communication  7.2.2. Analog and digital signals  7.2.3. Wireless and optical fibre communication  7.2.4. Radio Waves and Modulation

Grade 10 → Waves and optics → Light Waves and Optics ↓


Snell's Law


Light is an amazing phenomenon. It helps us see the world around us and adds color to our lives. But light isn't as simple as it seems. As we dive into the world of light and optics, one important concept we encounter is refraction. Refraction is the bending of light as it passes from one medium to another, such as from air to water. When this happens, we can use Snell's Law to predict how much the light will bend.

What is Snell's law?

Snell's law is a formula used to describe the relationship between the angles of incidence and refraction when light passes through the boundary between two different isotropic media, such as glass and air. In simple terms, it helps us understand how light bends when it passes through different substances.

n1 * sin(θ1) = n2 * sin(θ2)

Here, n1 represents the refractive index of the first medium, n2 is the refractive index of the second medium, θ1 is the angle of incidence, and θ2 is the angle of refraction.

Understanding the Components

Refractive index

The refractive index is a number that tells how fast light travels in a medium compared to the speed of light in a vacuum. For example, the refractive index of water is about 1.33, which means that light travels 1.33 times slower in water than in a vacuum. Different materials have different refractive indices, and this affects how much the light bends.

Angles of incidence and refraction

The angle of incidence is the angle between the incoming light ray and the normal (an imaginary line perpendicular to the surface at the point of incidence). The angle of refraction is the angle between the refracted ray and the normal.

Visual Example

Air Water N1 N2 Angle of incidence (θ1) Angle of refraction (θ2)

In this diagram, we see light traveling from air into water. The ray of light bends at the boundary. The angle it makes with the normal in air is the angle of incidence (θ1) and in water it is the angle of refraction (θ2).

How to Use Snell's Law

Suppose you know the angle at which the light hits the surface and the refractive indices of the two media. You can calculate the angle of refraction of light using Snell's law. Let's look at an example.

Example Problem

Imagine a ray of light striking a glass surface at an angle of 30°. The refractive index of air is 1.0, and the refractive index of glass is 1.5. We can use Snell's law to find the angle of refraction.

Use of Snell's Law:

n1 * sin(θ1) = n2 * sin(θ2)

Substituting the known values:

1.0 * sin(30°) = 1.5 * sin(θ2)

Solution for θ2 :

sin(θ2) = sin(30°) / 1.5
sin(θ2) = 0.5 / 1.5 = 0.3333
θ2 = arcsin(0.3333) ≈ 19.47°

The angle of refraction is about 19.47°.

Why does the light bend?

When light enters another medium, its speed changes. If it slows down, such as when entering water from air, it bends toward the normal. If it speeds up, it bends away from the normal. This change in direction is due to a change in momentum, which is caused by the different optical densities of different materials.

Some more examples and exercises

Example 1: Air to Water

If a ray of light strikes the surface of water at an angle of 45° and the refractive index of water is 1.33, what is the angle of refraction?

n1 * sin(θ1) = n2 * sin(θ2)
1.0 * sin(45°) = 1.33 * sin(θ2)
sin(θ2) = sin(45°) / 1.33
sin(θ2) = 0.7071 / 1.33 ≈ 0.5314
θ2 = arcsin(0.5314) ≈ 32.31°

The angle of refraction is about 32.31°.

Example 2: Prism Refraction

Imagine that light enters a glass prism at 60° from air. The refractive index of glass is 1.5. What is the angle of refraction inside the prism?

n1 * sin(θ1) = n2 * sin(θ2)
1.0 * sin(60°) = 1.5 * sin(θ2)
sin(θ2) = sin(60°) / 1.5
sin(θ2) = 0.8660 / 1.5 = 0.5773
θ2 = arcsin(0.5773) ≈ 35.26°

The angle of refraction is approximately 35.26°.

Importance and applications

Snell's law and the phenomenon of refraction are important in our everyday instruments, such as the lenses in eyeglasses, cameras, microscopes and telescopes. The law helps engineers design lenses to focus light precisely, to improve vision or to improve images in photography and scientific research.

Conclusion

Snell's Law is a fundamental principle that describes how light changes direction as it passes from one medium to another. By understanding the refractive index of the mediums and the angles of incidence and refraction, we can predict how light will behave. Through examples and practice, the concept becomes easier to understand.


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Snell's Law

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