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 → Electricity and Magnetism → Electric charge and static electricity ↓


Charging by friction, contact and induction


Electricity is a fascinating aspect of physics, and understanding how objects become electrically charged is an important part of the field. There are three primary methods through which an object can become charged: friction, contact, and induction. Each method has its own unique process and explanation. This lesson will explore these methods in detail using simple language, visual examples, and experiments that you might find in class.

Charging by friction

Charging by friction involves the transfer of electrons between two different materials when they are rubbed together. This process results in one material gaining electrons and the other losing electrons, creating a charge imbalance. Let us understand in detail how this happens.

When two different materials come into contact and are rubbed together, electrons can transfer from one material to the other. The material that loses electrons becomes positively charged, while the material that gains electrons becomes negatively charged. The extent to which an object can gain a positive or negative charge by friction depends on its position in the triboelectric series, which ranks substances based on their tendency to gain or lose electrons.

For example, when you rub a balloon on your hair, electrons transfer from your hair to the balloon, leaving your hair positively charged and the balloon negatively charged.

◯ Balloon (gains electrons, becomes negatively charged) <- Rubbing -> ◯ Hair (loses electrons, becomes positively charged)

Another example is rubbing a plastic rod with a cloth. Here, the electrons move from the cloth to the rod, leaving the rod negatively charged.

◯ Plastic rod (gains electrons, becomes negatively charged) <- Rubbing -> ◯ Cloth (loses electrons, becomes positively charged)

Charging by contact

Charging by contact involves touching a charged object to a neutral object, causing a transfer of electrons. When you touch a charged object to a neutral object, some of the electrons will move to balance the charge between them. This results in the neutral object becoming positively or negatively charged, depending on the direction of electron flow.

If a negatively charged rod touches a neutral metal sphere, the electrons will move from the rod to the sphere, leaving the sphere negatively charged.

◯ negatively charged rod __-/ Contact /-__ ◯ Neutral metal region (becomes negatively charged)

Conversely, if you bring a positively charged rod into contact with a neutral metal sphere, the electrons will flow from the sphere to the rod, and the sphere will become positively charged.

◯ positively charged rod __-/ Contact /-__ ◯ Neutral metal region (becomes positively charged)

Charging by induction

Charging by induction involves rearranging the distribution of electrons in a substance without direct contact. This method produces a charge in a nearby neutral object using the electric field created by a charged object. Induction charging is highly beneficial because it does not cause a direct transfer of electrons between the objects, which means the objects do not need to touch for charging to occur.

To understand this process, consider a neutral metal sphere near a negatively charged rod:

  1. When the negatively charged rod comes close to the neutral sphere, the electrons within the sphere are repelled, leading to separation of charges within the sphere.
  2. The part of the sphere closest to the rod becomes positively charged as the repelled electrons move toward the farther part, which is negatively charged.
  3. By grounding the sphere, you allow electrons to enter or exit the sphere to aid in balance.
  4. Once contact with the ground is broken, and the charged object is removed, the sphere remains free of a net charge due to the induction process.
◯ Negatively charged rod (repels the electrons in the sphere) ◯ Neutral metal region (left: positively charged side | right: negatively charged side) □ Earth (Grounding) Induced charge generation

Through induction, charging occurs without contact. This method is widely used in various technologies and provides a basis for understanding electrical grounding and insulation.

Imagining an example of induction

Imagine you are using a charged balloon and a neutral aluminum soda can.

  1. Bring the negatively charged balloon near the can without touching it.
  2. The electrons present in the can will be repelled by the balloon and move away, and the nearer part will remain positively charged.
  3. If you ground the can by touching it with your hand, the extra electrons will flow out of the can.
  4. Remove the grounding (your hand), then move the balloon away. The can remains in a net positive charge.
Charged balloon aluminum can Induced Fees

This process is an example of how everyday objects can become charged through the process of induction without direct contact.

Conclusion

Charging by friction, contact and induction are the three fundamental methods through which objects acquire an electrical charge. These concepts form the basis for understanding more complex electrical interactions and technologies. By rubbing, touching or simply bringing objects close to one another, charges are transferred or induced, causing substances to become charged. Understanding these principles provides insight into many natural phenomena and technological applications, from static cling to the mechanics of electric motors.

Friction charging relies on physical contact between materials, contact charging relies on direct electron transfer, and induction exploits the effect of electric fields. Each method demonstrates the dynamic nature of electric charges and their ability to power the modern world.

Through experiments and further exploration, one can develop a deeper understanding of how static electricity affects the environment and technology. Learning how to harness and control these charges through proper grounding and insulation techniques allows for the effective use of electricity and magnetism in practical applications.


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Charging by friction, contact and induction

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