Module 1 Electric Charge, Coulomb‘s Law

• Physicists in the 20th century came to recognize four different fundamental forces in nature.

              1.         Gravitational Force

              2.         Electromagnetic Force

              3.         Strong Nuclear Force

              4.         Weak Nuclear Force

   
• Like charges repel one another; unlike charges attract one another.
• Static electricity is a stationary electrical charge that is built-up on the surface of any material. It is the result of an imbalance between electric charges
• The word electricity comes from the Greek word “elektron” which means amber and is coined by English physician, William Gilbert.
• STATIC ELECTRICITY

  Typically, objects does not have a net charge. It is neither negatively or positively charged.

  In order for the object to accumulate a charge, a transfer of electrons is required.
• TriboElectric Effect – The process whereby two materials are rubbed together causing them to become charged with opposite signs.
• Electricity can be transferred through contact (triboelectric effect) or induction (electrostatic induction).
• Induced Charges - When there is no direct contact between two bodies but they can still be influenced by the presence of other charged body.
• CAUSES: STATIC ELECTRICITY

  In order for the object to have a charged, a transfer of electrons is required.

  Ways of Charging:

              1. Charging by Friction

              2. Charging by Conduction and Induction
• Charging by Friction

  One process to charge an object is through friction or known as triboelectric effect. It refers to the transfer of electrons from one object to another when both objects are rubbed together.
• Triboelectric effect tends to occur when both objects are electrically insulating, meaning the electrons cannot flow freely.

  When two objects are rubbed together and then separated, the surface of one object has gained a positive charge, while the surface of the other has gained a negative charge.
• Triboelectric series is a list that ranks materials according to their tendency to gain or lose electrons or what we called, electronegativity.

   
• Triboelectric Series Diagram The further away two materials from each other, the greater the charge transferred.

  Materials next to each other might not have become charged at all.

  Materials in neutral (middle) do not have strong tendency to give up or accept electrons.
• The ancient Greeks discovered as early as 600 BC that when they rubbed amber with wool, the amber could then attract other objects. It was discovered by the Greek philosopher, Thales of Miletus.

                                                                              
• Amber is a petrified or fossilized tree resin.
• In 1700, a French chemist, Guillaume du Fay, discovered that there were two different types of electricity.
• 1.When amber was rubbed with wool, it acquired so-called “resinous electricity”.

  2. When a glass was rubbed with silk, it acquired so-called “vitreous electricity”.

   
• They concluded that electricity repels electricity of the same kind, but attracts electricity of opposite kind.

  At this time, they thought that electricity was created by friction.
• In  18th Century, scientists came up with these:

  1.There were two types of charge: positive (vitreous) and negative (resinous).

  2. Like charges repel one another and  unlike charges attract.

  3.When two objects are rubbed together, charge can be transferred from one to the other, but the total charge remains constant.
• When amber is rubbed with wool, there is a transfer of charge such that the amber acquires a negative charge and the wool an equal positive charge.

  When glass is rubbed with silk, there is a transfer of charge such that the glass acquires a positive charge and the silk an equal negative charge.
• When the amber is rubbed with wool, there is a TRANSFER of electrons from the wool to the amber.

  The amber has now an excess of electrons and becomes a negatively charged.

  The wool has now a deficit of electrons  and becomes a positively charged.
• Matter is made up of atoms which contain three fundamental particles
• Electrons : coined by George Stoney

    discovered by J.J. Thomson
• Protons : coined by Ernest Rutherford

                   discovered by Ernest Rutherford
• Neutrons : coined by James Chadwick          

                      discovered by James Chadwick
• Two of these particles exhibit a property of electric charge.
• Electrons carry a charge of negative one “electron unit”.
• Protons carry a charge of positive one “electron unit”.
• Electron unit is also known as elementary charged, symbol: e.

   
• Electron Relative charge: -1e , Mass 9.11x10^-31kg
• Proton Relative Charge: +1e, Mass 1.67x10^-27kg
• Neutron Relative Charge: 0 , Mass 1.67x10^-27kg
• The net charge (Q_net) of any object is quantized, that is , the integral number of electron unit or elementary charge.

   

   

   Net charge (Q_net) contained by electrons (N_e), protons (N_p), and neutrons (N_n) is given by:

   
• LAW OF CHARGE CONSERVATION

  This is an example of a law of conservation of electric charges which states that “the net amount of electric charge produced in the process is zero” or “no net electric charge can be created nor destroyed”.
• The SI derived unit of quantity of electric charge is Coulomb, symbol: C.
• Coulomb is defined as the quantity of charge that passes through the cross section of an electrical conductor carrying one ampere for one second.
• Insulators

  • hold charges almost in fixed position
  • current will not flow
  • charges cannot re-arrange
• Conductors

  allow charges to move through them freely

  current flows easily

  charges may re-arrange themselves
• There is another type of materials in which its conductivity is like those of conductors and insulators.

  They can be pure elements such as silicon or germanium, or compounds such as gallium arsenide or cadmium selenide. These materials are called semiconductors.
• Insulators can be easily charged by friction as the extra electrons gained cannot easily escape.