News Todays 1

Electric charge is a fundamental property of matter with several key properties that define its behavior and interactions. Below is a detailed list of the properties of electric charges:

---

1. Quantization of Charge

• Electric charge is quantized, meaning it exists in discrete packets.
• The smallest unit of charge is the elementary charge (e), approximately (1.602 x 10^{-19}) coulombs.
• All observed charges are integer multiples of (e) (e.g., (e), (+2e), (-e), etc.).
• Quarks have fractional charges (+1/3e, +2/3e), but they are always confined in particles (e.g., protons, neutrons) that have integer charges.

---

2. Conservation of Charge

• Total charge in an isolated system is conserved; it can not be created or destroyed.
• Charge can only be transferred from one object to another.
• Example: In nuclear reactions, the total charge before and after the reaction remains the same.

---

3. Additivity of Charge

• The total charge of a system is the algebraic sum of all individual charges.
• Example: If a system has charges (+3e), (-2e), and (+e), the net charge is (+2e).

---

4. Two Types of Charge

• There are two types of electric charge: positive and negative.
• Like charges repel each other (e.g., two positive charges or two negative charges).
• Opposite charges attract each other (e.g., a positive charge and a negative charge).

---

5. Invariable of Charge

• Electric charge is independent of the motion of the charged particle.
• Charge remains the same regardless of the frame of reference (a consequence of special relativity).

---

6. Charge is a Scalar Quantity

• Electric charge has magnitude but no direction, making it a scalar quantity.
• However, the force and field associated with charges are vector quantities.

---

7. Charge Distribution

• Charges can be distributed in different ways:
  • Point Charge: A charge concentrated at a single point.
  • Surface Charge: Charge distributed over a surface (e.g., on a conductor).
  • Volume Charge: Charge distributed throughout a volume (e.g., in a charged insulator).
  • Linear Charge: Charge distributed along a line (e.g., on a thin wire).

---

8. Charge and Mass

• Charge is independent of mass. For example:
  • Protons and electrons have equal and opposite charges ((+e) and (-e)), but their masses are vastly different.
  • Neutrons have no charge but have mass.

---

9. Polarity of Charge

• Charges can exist as positive or negative.
• The polarity determines the direction of the electric field and the force experienced by other charges.

---

10. Interaction with Electric and Magnetic Fields

• A charged particle experiences a force in the presence of:
  • Electric Fields: (F = qE), where (E) is the electric field.
  • Magnetic Fields: (F = q(v x B)), where (v) is the velocity and (B) is the magnetic field.
• In the presence of both fields, the total force is given by the Lorentz Force:
  F = q(E + vB)

---

11. Charge in Conductors and Insulators

• Conductors: Charges can move freely (e.g., metals).
• Insulators: Charges are fixed and can not move freely (e.g., rubber, glass).
• Semiconductors: Charges can move under certain conditions (e.g., silicon, germanium).

---

12. Charge and Energy

• Work is done to move a charge in an electric field. This leads to changes in electric potential energy:
  U = qV
  where (V) is the electric potential.
• The energy stored in a system of charges depends on the product of the charges. It is inversely proportional to the distance between them.

---

13. Charge in Quantum Mechanics

• In quantum mechanics, charge is associated with the wave function of particles.
• Charged particles interact via the exchange of virtual photons, as described by Quantum Electrodynamics (QED).

---

14. Charge in Cosmology

• The universe is believed to be electrically neutral on large scales, with equal amounts of positive and negative charge.
• Charge plays a role in the behavior of plasma in stars, interstellar space, and other astrophysical phenomena.

---

Summary Table of Properties

Property	Description
Quantization	Charge exists in discrete packets (multiples of (e)).
Conservation	Total charge in an isolated system is constant.
Additivity	Net charge is the algebraic sum of individual charges.
Two Types	Positive and negative charges; like charges repel, opposite charges attract.
Invariance	Charge is independent of the motion of the particle.
Scalar Quantity	Charge has magnitude but no direction.
Distribution	Can be point, surface, volume, or linear.
Independent of Mass	Charge and mass are separate properties.
Polarity	Determines the direction of electric fields and forces.
Interaction with Fields	Experiences forces in electric and magnetic fields.
Conductors and Insulators	Charges move freely in conductors but not in insulators.
Energy	Work is done to move charges, changing electric potential energy.
Quantum Mechanics	Charge is a quantum number; interactions mediated by virtual photons.
Cosmology	Universe is electrically neutral on large scales.

---

Charging Techniques

1. Charging by Friction (Triboelectric Charging)

• Description: When two objects are rubbed together, electrons move from one material to the other. This occurs because of differences in their electron affinity.
• Mechanism:
  • One material loses electrons and becomes positively charged.
  • The other material gains electrons and becomes negatively charged.
• Examples:
  • Rubbing a glass rod with silk: The glass becomes positively charged, and the silk becomes negatively charged.
  • Rubbing a plastic comb on hair: The comb becomes negatively charged, and the hair becomes positively charged.
• Triboelectric Series: A list of materials ordered by their tendency to gain or lose electrons.

---

2. Charging by Conduction (Direct Contact)

• Description: A charged object is brought into direct contact with a neutral object, transferring charge between them.
• Mechanism:
  • If the charged object is negative, electrons are transferred to the neutral object.
  • If the charged object is positive, electrons are transferred from the neutral object.
• Result:
  • Both objects acquire the same type of charge.
• Example:
  • Touching a neutral metal sphere with a negatively charged rod: The sphere becomes negatively charged.

---

3. Charging by Induction

• Description: A charged object is brought near a neutral object without direct contact. This action causes a redistribution of charges in the neutral object.
• Mechanism:
  1. A charged object (e.g., negatively charged) is brought near a neutral conductor.
  2. Electrons in the conductor are repelled. This causes one side to become positively charged. The other side becomes negatively charged.
  3. If the conductor is grounded, electrons flow to or from the ground, leaving the conductor with a net charge.
  4. The ground connection is removed, and the charged object is taken away, leaving the conductor with an opposite charge.
• Result:
  • The neutral object acquires a charge opposite to that of the charged object.
• Example:
  • Bringing a negatively charged rod near a neutral metal sphere: The sphere becomes positively charged after grounding.

---

4. Charging by Polarization

• Description: A charged object induces a separation of charges in a neutral object without transferring charge.
• Mechanism:
  • The electric field of the charged object causes electrons in the neutral object to shift. This creates regions of partial positive and negative charge.
• Result:
  • The neutral object remains neutral overall but exhibits a dipole moment.
• Example:
  • Bringing a charged balloon near a wall: The wall’s surface becomes polarized, causing the balloon to stick.

---

5. Charging by Radiation (Photoelectric Effect)

• Description: Light or other electromagnetic radiation can eject electrons from a material, causing it to become charged.
• Mechanism:
  • Photons with enough energy (above the material’s work function) knock electrons out of the material.
• Result:
  • The material loses electrons and becomes positively charged.
• Example:
  • Ultraviolet light shining on a metal surface: Electrons are ejected, leaving the metal positively charged.

---

6. Charging by Heating (Thermionic Emission)

• Description: Heating a material can cause electrons to gain enough energy to escape, resulting in a net charge.
• Mechanism:
  • At high temperatures, electrons in a material gain thermal energy and are emitted from the surface.
• Result:
  • The material loses electrons and becomes positively charged.
• Example:
  • Heating a metal filament in a vacuum tube: Electrons are emitted, creating a positive charge on the filament.

---

7. Charging by Chemical Reactions (Electrochemistry)

• Description: Chemical reactions can transfer electrons between substances, creating charged ions.
• Mechanism:
  • Oxidation (loss of electrons) and reduction (gain of electrons) occur concurrently in a redox reaction.
• Result:
  • The reactants become charged ions.
• Example:
  • In a battery, chemical reactions at the electrodes create a potential difference, resulting in a flow of electrons.

---

8. Charging by the Van de Graaff Generator

• Description: A device that uses a moving belt to accumulate electric charge on a metal dome.
• Mechanism:
  1. A belt rubs against a comb, transferring charge to the belt.
  2. The belt carries the charge to the metal dome, where it is transferred via another comb.
  3. The process continues, building up a high voltage on the dome.
• Result:
  • The dome becomes highly charged, either positively or negatively, depending on the design.
• Example:
  • Used in physics demonstrations and particle accelerators.

---

Summary of Charging Techniques

Method	Mechanism	Result
Friction	Rubbing two materials transfers electrons.	Objects acquire opposite charges.
Conduction	Direct contact transfers charge.	Objects acquire the same charge.
Induction	A charged object induces charge separation without contact.	Neutral object acquires an opposite charge.
Polarization	A charged object causes charge separation in a neutral object.	Neutral object develops a dipole moment.
Radiation	Light ejects electrons from a material.	Material becomes positively charged.
Heating	Heat causes electrons to escape from a material.	Material becomes positively charged.
Chemical Reactions	Redox reactions transfer electrons between substances.	Reactants become charged ions.
Van de Graaff	A belt system accumulates charge on a metal dome.	Dome becomes highly charged.

---

Applications of Charging Techniques

• Electrostatic Precipitators: Remove particulate matter from industrial exhaust gases.
• Photocopiers and Laser Printers: Use electrostatic principles to transfer toner to paper.
• Particle Accelerators: Use charging techniques to manipulate charged particles.
• Batteries and Fuel Cells: Rely on electrochemical charging techniques to store and release energy.

Millikan experiment

Coulomb’s Law

Electric field