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 → Properties of matter → Pressure ↓


Surface tension and capillarity


In the study of physics and when looking at the properties of matter, two fascinating phenomena come to light: surface tension and capillarity. These are observable effects that arise from the interaction between molecules in a liquid and the forces that act upon them. To understand the world around us, it is important to understand how these forces work and why they are important.

What is surface tension?

Surface tension is a property of the surface of a fluid that allows it to behave somewhat like an elastic sheet. It arises due to cohesive forces between fluid molecules. Imagine the surface of a fluid as if it were covered by a thin elastic membrane. This 'membrane' is not visible, but provides enough tension to support very light objects, such as paper clips or bugs, on the surface without them sinking.

Visual example: water molecules on the surface Cohesive Force

In this diagram, the blue circle represents a water molecule. The dashed lines represent the cohesive forces acting on it.

The science behind surface tension

Molecules in a fluid are attracted to each other with a force called cohesion. Molecules within a fluid are pulled equally in all directions by their neighbouring molecules. This results in a zero net force.

However, molecules on a surface do not have molecules on all sides; they are only pulled sideways and inward by neighbors. This uneven force pulls surface molecules into a tight layer, producing an effect known as surface tension.

Mathematical expression

Surface tension is usually represented by the symbol σ. It can be expressed mathematically as the force per unit length:

σ = F/L

Where:

  • σ is the surface tension
  • F is the force applied on the fluid
  • L is the length over which the force acts

Examples of surface tension in everyday life

  • Water drops: Have you ever wondered why water forms round drops? This is the work of surface tension, which tries to minimize the surface area.
  • Paper clip floating on water: You can gently place a small paper clip on the surface of water and watch it float due to surface tension.
  • Insects that walk on water: Some insects can walk on water without sinking because of the surface tension resisting their weight.

What is capillarity?

Capillarity or capillary action is the ability of a fluid to flow into narrow spaces without the aid of external forces (such as gravity). It is caused by adhesive forces between the fluid and the surrounding solid surface as well as cohesive forces between the fluid molecules.

In simple words, it is the phenomenon you see when water rises in a thin tube, despite gravity.

Visual example: Water tube Capillary growth

This tube demonstrates the concept of capillarity, where water rises inside a narrow tube.

The science behind capillarity

Capillarity is the result of two types of forces: cohesive and adhesive. Cohesive forces act between similar molecules, while adhesive forces act between different types of molecules.

When adhesive forces (between a liquid and a solid surface) are stronger than cohesive forces, the liquid will "climb" the surface, a phenomenon called capillary action. If the liquid molecules had greater cohesion, the liquid would not climb as high.

The height to which the liquid rises in the capillary tube can be calculated using the formula:

h = (2T * cos(θ)) / (r * ρ * g)

Where:

  • h = the height to which the liquid rises
  • T = surface tension of the liquid
  • θ = contact angle of the liquid
  • r = radius of the tube
  • ρ = density of the liquid
  • g = acceleration due to gravity

Examples of capillarity in daily life

  • Soil Moisture: Capillary action helps water flow from the subsoil to the topsoil, which is essential for plant growth.
  • Ink on paper: When you write with a pen on paper, the ink spreads slightly due to capillary action.
  • Rise of oil up the wick: In a candle or lamp, oil rises up the wick due to capillarity.

Real-world applications

Surface tension and capillarity are not just academic topics, they have important applications in the real world:

Surface tension applications

  • Soap Bubbles: The formation of soap bubbles is an example of surface tension. Adding soap to water reduces the surface tension, causing bubbles to form and last longer.
  • Detergents: Detergents reduce the surface tension of water, making it easier for the water to spread and penetrate fibers to remove dirt and oils.
  • Inks and Paints: Understanding surface tension is essential to the formulation of inks and paints to ensure proper dispersion and adhesion to a surface.

Capillary action applications

  • Medical tests: Capillarity is used in a number of diagnostic tests; for example, drawing blood using capillary tubes.
  • Plants and trees: Plants use capillarity to transport water and nutrients from the roots to the leaves, which is necessary for photosynthesis.
  • Microfluidic devices: Microfluidic devices use capillary action to manipulate small volumes of fluids for applications in biochemical tests.

Closing thoughts

Understanding surface tension and capillarity helps us understand a wide range of natural phenomena and technological applications. These concepts explain why objects can float, how liquids can rise to surfaces, and have many uses in industries. As you learn more about forces in nature, you'll see how interconnected and fascinating the different principles of physics can be.


Grade 10 → 2.2.6


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Surface tension and capillarity

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