Electricity Lecture Notes PDF

Electricity What is electricity? The collection or flow of electrons in the form of an electric charge  What is the difference between static electricity and current electricity? Static electricity is stationary or collects on the surface of an object, whereas current electricity is flowing ve...

Electricity What is electricity? The collection or flow of electrons in the form of an electric charge  What is the difference between static electricity and current electricity? Static electricity is stationary or collects on the surface of an object, whereas current electricity is flowing very rapidly through a conductor. What Is Static Electricity?  A stationary electrical charge that is built up on the surface of a material  Where do charges come from? Matter is made up of atoms. + Proton (positive charge) – neutron (neutral) + + + – electron (negative charge) – – atom nucleus  Where do charges come from? If electrons = protons neutral If electrons > protons  gaining electrons, negative charge If electrons < protons  losing electrons, positive charge  Insulators and conductors Insulators: materials that do NOT allow electrons to flow through them easily. Insulators can be easily charged by friction as the extra electrons gained CANNOT easily escape.  4 Insulators and conductors Conductors: materials that allow electrons to flow through them easily. Conductors CANNOT be easily charged by friction as the extra electrons gained can easily escape. Electrostatic Force  Law of Charges Like charges repel and opposite charges attract + + - - + -  Note that electricity is different from gravitation, in which the force is always attractive m1 m2 February 27, 2020 23  The Unit of Charge  The unit of charge is the coulomb, abbreviated C  The coulomb is defined in terms of the SI unit for electric current, the ampere, abbreviated A  The ampere is a basic SI unit like the meter, the second, and the kilogram.  The unit of charge is defined as 1 C=1As February 27, 2020 24  Charge of an Electron  We can define the unit of charge in terms of the charge of one electron An electron is an elementary particle with charge q = -e where e = 1.602 · 10-19 C A proton is a particle with q = +e e = 1.602 · 10-19 C February 27, 2020 25  Coulomb of Charge  A full coulomb is a very large amount of charge!  The number of electrons required to produce 1 coulomb of charge is 1C Ne   6.24 1018 1.602 10 -19 C  Because a coulomb is a large amount of charge, everyday examples of static electricity typically involve 1 micro coulomb = 1 C = 10-6 C 1 nano coulomb = 1 nC = 10-9 C 1 pico coulomb = 1 pC = 10-12 C February 27, 2020 26  Insulators and Conductors  The electronic structure of materials determines their ability to conduct electricity “Conducting electricity” means the transport of electrons  Materials that conduct electricity well are called conductors Electrons can move freely (i.e., some of the electrons) Metals Water with dissolved materials  Materials that conduct electricity poorly are called insulators Electrons cannot move freely Glass Pure water February 27, 2020 27  Semiconductors  Semiconductors are materials that can be switched between being an insulator and being a conductor.  Semiconductors are the backbone of modern electronics and computers. Replica of first transitor Modern computer chip with in 1947 millions of transitors February 27, 2020 28  Electric Force - Coulomb’s Law  Consider two electric charges: q1 and q2  The electric force F between these two charges separated by a distance r is given by Coulomb’s Law kq1q2 F 2 r  The constant k is called Coulomb’s constant and is given by k  8.99 10 Nm /C 9 2 2 February 27, 2020 33  Coulomb’s Law (2)  The coulomb constant is also written as 1 C2 k where  0  8.85 10 12 4  0 Nm 2  0 is the “electric permittivity of vacuum” A fundamental constant of nature 1q1q 2 F 4 0 r 2 February 27, 2020 34  Example: Force between Two Charges  What is the force between two 1 C charges 1 meter apart? 1 q1q 2 F 4 0 r 2  9 N  m  1 C 1 C 2 F   8.99 10   1 m  2 2  C  8.99 109 N which is the weight of 450 Space Shuttles at launch February 27, 2020 35  Electric Force  The electric force is given by q1q2  The electric force, unlike the gravitational force, can be positive Fk 2 or negative r If the charges have opposite signs, the force is negative + - Attractive If the charges have the same sign, the force is positive + + Repulsive - - February 27, 2020 36 Two equally charges (q2&q1( )0.8x10-9C ) one +ve and one –ve separated by r= 0.1m ‫المؤثرة على‬calculate electric force on third charge qo= 0.4x10-9C )if it puted at a&b. as shown q2 aq q1 At point a - +3 0.04m + 0.06m r=0.1m r=0.1m r=0.1m b At point b - + + q2 F2 q1 F1 q3 calculate electric force affected on q2 due to ‫؟‬q1 and q3 as shown in figure. - q =1.2ϻc 3 F2 5cm F1 + q =2.5ϻc 2 - q =3.6ϻc 1 5cm find electric force on q3 due to q1 and 3‫مثال‬ q2 as shown below