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 → Electricity and Magnetism → Electrostatics ↓


Coulomb's law


In the world of physics, one of the fundamental concepts to understand is how objects interact with each other through forces. Among a series of forces, electrostatic forces stand out as fundamental interactions that explain much about how objects behave at the atomic level. Coulomb's law is the principle that describes the forces acting between charged objects.

Understanding the charge

Before we dive into Coulomb's law, it's important to understand what charge is. All matter is made up of atoms, which contain protons, neutrons, and electrons. Protons have a positive charge, electrons have a negative charge, and neutrons are neutral. In general, the charge of a substance depends on the balance between protons and electrons. If there are more electrons than protons, the object becomes negatively charged. Similarly, if there are more protons than electrons, the object is positively charged.

Imagine you are playing with two balloons. Before you begin, both balloons are hanging neutrally, unaffected by each other. Now imagine you are rubbing both balloons on your hair. What happens next is magical and deeply rooted in Coulomb's law.

The essence of Coulomb's law

Coulomb's law describes how charged objects interact with each other. This law states that the force between two charged objects is proportional to the magnitude of their charges and inversely proportional to the square of the distance between them.

F = k * (|q1 * q2| / r²)

Where:

  • F is the force between the charges (in newtons).
  • q1 and q2 are the magnitudes of the charges (in coulombs).
  • r is the distance (in meters) between the centres of the two charges.
  • k is the Coulomb constant, approximately 8.9875 × 10^9 N m²/C².

Visual example

R

In the figure above, two circles represent charged particles. The line between them is r, which is the distance separating the two charges. According to Coulomb's law, the force between these two particles is affected by their charges and this distance.

Exploring the elements of law

Magnitude of charge

Consider two charged particles. If both particles have charge, the force between them will also increase as the magnitude of these charges increases. This relationship is directly proportional, meaning that if you double one of the charges, the force also doubles. For example, if you have two charges, q1 = 3C and q2 = 2C, and you change q1 to 6C, the force will also double, assuming the distance remains constant.

Distance between charges

Coulomb's law also tells us that the force is inversely proportional to the square of the distance between the charges. This means that as the distance between two charges increases, the force between them decreases. Conversely, as the distance decreases, the force becomes stronger.

To visualize:

Initial Increased

In the above diagram, in the second scenario as the distance between the charges increases, the force decreases according to the inverse square relationship.

Coulomb constant

The constant k in Coulomb's law provides the proper proportionality for the equation. It converts the proportional relationship into exact quantities. Its value is approximately 8.9875 × 10^9 N m²/C², which is determined through experimental means.

Sign of charges and type of interaction

Charges can be of two types: positive or negative. The type of attraction or repulsion depends on the nature of these charges.

  • Like charges repel each other: a positive charge repels another positive charge, and a negative charge repels another negative charge.
  • Unlike charges attract each other: positive charge attracts negative charge, and vice versa.

Example: positive and negative charge

Attraction

The figure above shows a positive and a negative charge attracting each other. This follows the rule that opposite charges attract each other.

Applications of Coulomb's law

Coulomb's law is not just theoretical; it has important practical applications in the real world. It explains many phenomena in chemistry, physics, engineering, and other fields:

Atoms and molecules

At a fundamental level, Coulomb's law is important for understanding how atoms form chemical bonds. Electrons are attracted to the positively charged nuclei of atoms, which helps form molecules.

Electronics

In electronics, Coulomb's law helps in designing and understanding the behavior of capacitors, insulators, and semiconductors. The force between charged particles is important in designing circuits.

Examples from daily life

  • When you drag your feet across a carpet and then touch a metal door handle, the shock you feel is a demonstration of the transfer of charges.
  • Another practical example is that hairs repel each other due to static electricity.

Conclusion

Coulomb's law is an important principle that underlies our understanding of the interactions between charged objects. By describing the electric force as a simple function of charge magnitudes and distances, it provides profound insight into the structure of matter. Although its equation is simple, its implications reach into the complexities of the chemistry and physics that govern our universe.


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Coulomb's law

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