Electrostatics

Electrostatics

• It is a branch of Physics that studies slow-moving or stationary electric charges.

• It is the study of electromagnetic phenomena that occur when there are no moving charges.

  
  

Law of Electrostatics

• Like charges repel; opposite charges attract.

• This is due to the nature of the electric force, which is a force that is exerted between two particles that have either opposite charges or similar charges.

  
  

Electrical Charge

There are two types of electrical charges as suggested by Benjamin Franklin:

• Positive

  • associated with protons

  • any particle that contains less electrons than protons

• Negative

  • associated with electrons

  • contain more electrons than protons

    
    

Electrically Neutral

• If an atom contains an equal number of protons and electrons

  
  

Electrically Charged

• If the atom contains an unequal number of protons and electrons

  
  

SI Unit for the Electric Charge

• Coulomb’s (C) in honor of French physicist Charles de Coulomb.

  
  

Properties of Electrical Charge:

• Charge is Conserved

  • The total charge in an object is the algebraic sum of all individual charges (electrons and protons) carried by the object.

  • In any close system, the algebraic sum of all electric charges remain the same.

• Charge is Quantized

  • The magnitude of the charge of any body is always an integral
    multiple of the elementary charge e.

  • Electric charge cannot be divided into amounts smaller than the
    charge of one electron or proton.

  • Hence, the charge of any macroscopic body is always either
    zero (neutral) or an integral multiple of e.

Conductors

• Those which allow electrons to freely move across the entire material.

• Copper, the substance used in your electrical wirings at home, is a good conductor of electrons.

• Most metals are good conductors.

Insulators

• Materials that impede the free flow of electrons.

• The particles of an insulator do not allow the free flow of electrons and charge is seldom distributed evenly across the entire material.

• Rubber, a material used to cover electrical tools, is a good insulator.

• Most nonmetals are good insulators.

Semiconductors

• Materials that are intermediate in their properties between good conductors and insulators.

• Silicon is the one of the most used semiconductor.

Charge Transfer Mechanisms

• Charging by Friction

  • Charging by friction also known as triboelectric charging is a process in

    which two objects become electrically charged when rubbed together. it

    works by:

  • Electron Transfer: When two materials are rubbed together, electrons are

    transferred from one material to the other.

  • Charging Effect: One material loses electrons and becomes positively

    charged, while the other material gains those electrons and becomes

    negatively charged.

    
    

• Charging by Conduction

  • Charging by conduction also called charging by contact is a process where a charged object directly touches a neutral object, allowing electrons to transfer between them. This results in the neutral object gaining the same type of charge as the charged object.

  • It works by:

    1. A charged object (either positive or negative) comes into direct contact with a

    2. neutral object.

    3. Electrons transfer between the two object.

    4. After contact, both objects have the same type of charge.

       
       

• Charging by Induction

  • Charging by induction is a method of charging a neutral object without direct contact with a charged object. Instead of transferring electrons directly, the presence of a charged object polarizes the charges in the neutral object, and grounding is often used to complete the process.

  • It works by:

    1. Bring a charged object close to a neutral object.

       • This causes the charges in the neutral object to rearrange (polarization).

    2. Ground the neutral object (if needed).

       • If you touch the neutral object, electrons will either enter or leave depending on the charge
         nearby.

    3. Remove the ground, then remove the charged object.

       • The neutral object now has a permanent charge, opposite to the charge of the original
         object.

       
       

• Charging by Grounding

  • Grounding is a method of neutralizing or charging an object by connecting it to a large reservoir of charge, like the Earth. The ground can supply or absorb electrons as needed. How it works:

    1. A charged object is brought near a neutral object.

       • This causes the neutral object's charges to rearrange (polarization).

    2. The neutral object is connected to the ground.

       • If the object is negatively charged, excess electrons flow to the ground.

       • If the object is positively charged, electrons from the ground flow into it.

    3. The ground connection is removed first, then the charged object.

       • The object now has a charge opposite to the original charged object.

         
         

Coulomb’s Law

• States that the force between two charged objects is proportional to
  the product of their charges and inversely proportional to the square
  of the distance between them.

  
  

  

  • where F is the force, Q1 and Q2 are the charges, r is the distance between the charges, and k is the Coulomb constant.

  
  

  States two important relations.

  • Electrostatic force is:

    1. Directly proportional to the product of the charges; and

    2. Inversely proportional to the square of the distance between them.

Direction of the force

• An attractive electrostatic force occurs when two particles with opposite charges pull towards each other.

• Repulsive electrostatic force happens when two particles with the same charge push away from each other; essentially, opposite charges attract, and like charges repel.

  
  

Example:

• Attractive electrostatic force:

  • The force between a proton (positive) and an electron (negative) in an atom. repulsive electrostatic

• Repulsive electrostatic force:

  • The force between a proton (positive) and an electron (negative) in an atom.

• Electrostatic Force

  • It's the attractive or repulsive force between two electrically charged objects.

  • It is analogous to the famous Law of Gravitation formulated by Isaac Newton.