Language: English বাংলা

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Atoms
Static Electricity: Study Notes 🔍 Introduction Static electricity refers to the accumulation of electric charges on the surface of materials. Unlike current electricity, which involves the flow of electrons through a conductor, static electricity remains stationary until discharged. This phenomenon is commonly observed in everyday life—like when your hair stands up after removing a woolen cap or when a balloon sticks to a wall after being rubbed against your clothes. ⚛️ Atomic Basis of Static Electricity All matter is made up of atoms, which consist of: Protons (positive charge) Electrons (negative charge) Neutrons (neutral) Normally, atoms are electrically neutral because they contain equal numbers of protons and electrons. However, when two materials come into contact and are then separated, electrons may transfer from one to the other, creating an imbalance. This imbalance results in one object becoming positively charged (loss of electrons) and the other negatively charged (gain of electrons). 🧪 How Static Electricity Is Created Static electricity is typically generated through friction. When two different materials are rubbed together, electrons may move from one to the other depending on their electron affinity. Common examples include: Rubbing a balloon on hair: Balloon becomes negatively charged. Rubbing a glass rod with silk: Glass becomes positively charged. This process is called triboelectric charging, and the tendency of materials to gain or lose electrons is ranked in the triboelectric series. ⚡ Properties of Static Charges Like charges repel, and unlike charges attract. Charges can be transferred by conduction (direct contact) or induction (without contact). A charged object can attract neutral objects due to polarization. 🧲 Conductors vs. Insulators Conductors (e.g., metals): Allow free movement of electrons; static charge does not build up easily. Insulators (e.g., plastic, rubber): Restrict electron flow; ideal for generating and holding static charge. 🌐 Electrostatics: The Study of Static Charges Electrostatics is the branch of physics that deals with stationary electric charges. Key concepts include: 1. Electric Field (E) A region around a charged object where other charges experience a force. Direction: Away from positive charges, toward negative charges. Measured in newtons per coulomb (N/C). 2. Electric Field Lines Imaginary lines representing the direction of the electric field. Properties: Never cross. Denser lines indicate stronger fields. 3. Coulomb’s Law Describes the force between two point charges: 𝐹 = 𝑘 𝑞 1 𝑞 2 𝑟 2 Where: 𝐹 = electrostatic force 𝑞 1 , 𝑞 2 = magnitudes of charges 𝑟 = distance between charges 𝑘 = Coulomb’s constant ( 8.99 × 10 9   𝑁 𝑚 2 / 𝐶 2 ) 🧮 Charging Methods 1. Friction Rubbing two objects transfers electrons. Example: Rubbing a comb on hair. 2. Conduction Direct contact transfers charge. Example: Touching a charged rod to a neutral metal sphere. 3. Induction Bringing a charged object near a neutral one causes redistribution of charges. No direct contact required. 🧯 Discharging Static Electricity Static charges can be neutralized by: Grounding: Connecting to Earth allows excess charge to flow away. Moisture: Humid air helps dissipate charges. Conductive materials: Provide a path for charge to escape. 🧰 Applications of Static Electricity 1. Electrostatic Precipitators Used in industries to remove dust and smoke from exhaust gases. 2. Photocopiers and Laser Printers Use static charge to attract toner particles to paper. 3. Painting and Coating Electrostatic spray painting ensures even coating and reduces waste. 4. Air Purifiers Use static charge to trap dust particles. ⚠️ Hazards of Static Electricity Fire and Explosion Risk: In flammable environments, static discharge can ignite vapors. Electronic Damage: Sensitive components can be destroyed by electrostatic discharge (ESD). Shock: Mild shocks from touching metal objects after walking on carpet. To prevent hazards: Use antistatic wristbands. Install grounding chains on fuel trucks. Maintain humidity in workspaces. 🧪 Experiments and Demonstrations 1. Balloon and Hair Rub a balloon on hair and observe attraction. 2. Comb and Paper Rub a plastic comb on wool and use it to pick up small paper bits. 3. Electroscope Device used to detect electric charge. Consists of metal leaves that diverge when charged. 🧠 Summary Static electricity arises from imbalance of charges. It is generated by friction, conduction, or induction. Electrostatics explains the behavior of stationary charges. It has practical applications but also poses risks. Understanding static electricity is essential in physics and engineering.
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Cell

Notes on Water Cycle:

  • Evaporation: Water from oceans, rivers, and lakes turns into vapor due to the sun’s heat.
  • Condensation: Water vapor rises, cools, and forms clouds in the atmosphere.
  • Precipitation: Clouds release water as rain, snow, or hail back to the earth.
  • Collection: Water gathers in oceans, rivers, lakes, and underground sources.

The water cycle is a continuous process that maintains the balance of water on earth and supports all living organisms.

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