1 ECE 101 Exploring Electrical Engineering Chapter 5 Circuit Elements Herbert G. Mayer, PSU Status 1/30/2016 Derived with permission from PSU Prof. Phillip Wong

2 Syllabus Electric Charge Electric Charge Electric Field Electric Field What is Conductance What is Conductance References

3 Intro Many SI units you saw earlier Many SI units you saw earlier Now we discuss detail of a few key SI units With their: name, symbol, equation, unit etc.

4 Electric Charge Electric charge ( q or Q ) is an intrinsic property of certain subatomic particles Electric charge ( q or Q ) is an intrinsic property of certain subatomic particles A particle’s charge affects its motion in the presence of electric and also in magnetic fields A particle’s charge affects its motion in the presence of electric and also in magnetic fields The SI unit for electric charge is the coulomb [C] The SI unit for electric charge is the coulomb [C] 1 [C] = 1 [A] * 1 [s] The charge of 1 electron is ≈ 1.602× C The charge of 1 electron is ≈ 1.602× C Can be positive or negative Can be positive or negative

5 Electric Field Lorentz Force Law → The force F, acting on a charged particle in the presence of an electric field and a magnetic field is: Lorentz Force Law → The force F, acting on a charged particle in the presence of an electric field and a magnetic field is: If the magnetic field is zero, then the electric field that pervades the space around the charge is: If the magnetic field is zero, then the electric field that pervades the space around the charge is: FqFq E = F, E, B, & v are vectors q = electric charge of the particle v = velocity of the particle E = electric field, B = magnetic field

6 What Is? An electron? Subatomic particle with electric charge; we call that charge negative Electron is part of the lepton family Called an elementary particle, since it seems to have no sub-particles Has mass of approx. 1/1836 of a proton Yet electrons have some properties of particles AND waves

7 What Is? Coulomb is the fundamental unit of electrical charge And identifies the SI derived unit of electric charge Symbol for Coulomb is C; the symbol for charge flowing, creating a current, is: Q or q A coulomb is equal to a charge of × electrons (or protons) What exactly a charge really is, we don’t understand, but we do know some key properties, and we can measure such properties quite accurately Similar to gravity: we can measure and use it, even fly to the moon with rockets overcoming gravity, but don’t fundamentally understand how gravity works; theories exist

8 7 SI Base Units: No Coulomb, No Volt

9 7 SI Base Units

10 Units Derived from 7 SI

11 What was Ampere Again? Unit of current. One of the base units of the SI Named after André Marie Ampère, French physicist 1775 – 1836 When about × electrons stream though a conductor in 1 second, the charge moved is 1 C and the current is 1 A; ACA “amp”. i = dq / dt 1 A = 1 C / s assumes even flow of current during one second s

12 AC DC Current Carriers of charge may be: Carriers of charge may be: Electrons - Ions + Holes + In direct current (DC), charge carriers move in one direction, viewed macroscopically In direct current (DC), charge carriers move in one direction, viewed macroscopically In alternating current (AC), charge carriers alternate direction periodically; frequency in Hertz [Hz] In alternating current (AC), charge carriers alternate direction periodically; frequency in Hertz [Hz] SI unit for current is ampere is A = C / s SI unit for current is ampere is A = C / s Picture of physicist André-Marie Ampère Picture of physicist André-Marie Ampère André Ampère

13 What is? We discussed definition of Volt, Power, Resistance Discuss inverse of resistance: Conductance In later presentation we discuss Ohm’s Law in detail Here highlight:

14 Ohm’s Law At constant temperature, the current I through some material is directly proportional to the potential difference ΔV between its ends; Δ is generally omitted! At constant temperature, the current I through some material is directly proportional to the potential difference ΔV between its ends; Δ is generally omitted! I ≈ ΔV The resistance R is defined as: The resistance R is defined as: The general form of Ohm’s Law is: The general form of Ohm’s Law is: Georg Ohm

15 Application of Ohm’s Law Given:Material of known resistance R Voltage V is applied across the material Result:Current I = V / R will flow through it. Given:Material of known resistance R Known current I flowing through it Result:Voltage V = I · R exists across the material (known as a “voltage drop”). Given:Known voltage V across the material Known current I through the material Result:Resistance of the material is R = V / I.

16 What is? Conductance G is a measure of the ease with which a current flows through a material; i.e. it is the reciprocal of resistance: Conductance G is a measure of the ease with which a current flows through a material; i.e. it is the reciprocal of resistance: Ohm’s Law in terms of conductance (I below, not 1): Ohm’s Law in terms of conductance (I below, not 1): SI unit for conductance is Siemens [S], the inverse of resistance SI unit for conductance is Siemens [S], the inverse of resistance

17 References 1. 1.Ohm’s law: