1. 1 Explorers Computer Technology Post 631 October 14 and 21, 2010 by Don Braun (last modified on 10/28/2010) Fundamentals of Electricity and Electronics

2. 2 What is electricity? Electricity is the motion of electrically charged particles. The path of that motion is called a circuit. 1.Understand basic concepts and terminology of electricity and electronic devices, plus gravitational, electric, and magnetic fields. 2.Introduce some components and principles behind “Arduino” kits we will use to experiment with computer circuitry. Goals of this lesson Why are we talking about electronics? This will help us understand the hardware of stored-program electronic digital computers. This information is not really necessary to use computer software, which is the main subject of our Explorers Computer Technology Post 631.

3. 3 The Atomic Theory of Matter: 1.Two kinds of electric charges exist, called positive (+) and negative (–). 2.Like charges (+ with +, or else – with –) repel each other, while opposite charges (+ with –) attract each other. 3.All matter consists of atoms. 4.Every atom consists of a compact nucleus with protons (charge + e ) and neutrons (no charge), surrounded by electrons (charge – e ) that orbit the nucleus in shells, where e  1.60218  10 –19 coulomb. 5.The number of protons (i.e., the atomic number of the element) identifies the type of atom. For example: hydrogen has 1 proton, helium has 2 protons, carbon has 6 protons, uranium has 92 protons. What are electric charges and where do they come from?

4. 4 Terminology and symbols for charge, current, and voltage Physical quantity and notation SI units (the International System of Units) Symbol in an electrical diagram electric charge (Q) coulombs = C current (I) amperes = amps = A == Current at a point in a circuit is the amount of charge flowing past per unit time voltage (V), also called electric potential or electromotive force (EMF) volts = V = == Voltage (such as across a battery) between two points in a circuit measures “push” on current in units of energy per unit charge Q I V +–

5. 5 Water / electricity analogy for charge, current, and voltage http://hyperphysics.phy-astr.gsu.edu/hbase/electric/watcir.html#c1

6. 6 Terminology and symbols for a resistor and potentiometer Physical quantity and notation SI units (the International System of Units) Symbol in an electrical diagram resistance (R) of a resistor (which dissipates electrical energy by converting it to heat) ohms =  == By Ohm’s Law (V = I R) current I through resistor R produces voltage V total resistance (R) of a potentiometer ohms =  == The wiper of the potentiometer varies the resistance between it and either end V + – I R V + – R I bright off wiper light bulb direct current (DC) voltage source resistor

7. 7 Water / electricity analogy for current, voltage, and resistance http://hyperphysics.phy-astr.gsu.edu/hbase/electric/watcir.html#c1 + –

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9. 9 Terminology and symbols for a diode and an LED Physical quantity and notation SI units (the International System of Units) Symbol in an electrical diagram a diode allows current to flow easily in one direction, but nearly stops current in the opposite direction large forward-biastiny reverse-biascurrent thru diode a light emitting diode (LED) shines brightly with current in one direction, but it is dark if the opposite direction is attempted V + – large I R V + – tiny I R ++ V + – large I R V + – tiny I R ++ bright (on) dark (off) LED’s longer lead LED’s shorter lead black bandblack

10. 10 Water / electricity analogy for a diode & current-limiting resistor 47.5 11.4 valve diode + –

11. 11 Terminology and symbols for an inductor and a capacitor Physical quantity and notation SI units (the International System of Units) Symbol in an electrical diagram inductance (L) of an inductor (stores energy in a magnetic field created by current through a coil of wire) henries = H == Voltage is proportional to the rate of change of current through the inductor capacitance (C) of a capacitor (stores electrical energy in an electric field created by opposite charges on 2 conductors) farads = F == Current is proportional to the rate of change of the voltage across the capacitor V + – I L I(t)I(t) + – C I V(t) Q(t)Q(t)  Q(t) Q(t)

12. 12 Technical questions from Explorers after Oct. 14 th Meeting 1.Explain more about the history of electronics. 2.What is an electric field? 3.What is a magnetic field? 4.What is an electromagnetic field? 5.What is an inductor used for? 6.What makes a magnetic field collapse (in an inductor)? 7.How does a transformer work? 8.How do microprocessors work?

13. 13 Fields That Can Exert Forces; Important Early Physicists Gravitational field Isaac Newton 1642 – 1727 Electric field Charles-Augustin de Coulomb 1736 – 1806 Magnetic field Hans Christian Oersted 1777 – 1851 Electromagnetic field James Clerk Maxwell 1831 – 1867

14. 14 1.Isaac Newton (1642 – 1727) introduced a quantitative gravitational field theory to explain how objects fall toward Earth, the Moon orbits Earth, and planets orbit the Sun the way they do. 2.Gravity surrounds any particle that has a mass m 1 [SI units of kilograms]. 3.The acceleration due to the gravitational field at distance r from the center of a spherical mass m 1 is, always directed toward mass m 1, where G is called Newton’s universal gravitation constant. Gravitational Field Close objects accelerate faster than far objects

15. 15 4.For example, on the surface of Earth the acceleration of gravity is about directed toward the center of the earth. 5.That field exerts an attractive force on another particle with mass m 2 at a distance r from mass m 1 with magnitude by Newton’s Law of Gravity. Gravitational Field (continued)

16. 16 1.Charles Coulomb (1736 – 1806) introduced a quantitative electric field theory to explain how charged objects exert forces that attract or repel each other. 2.The electric field (denoted by E with SI units of newtons/coulomb = volts/meter) surrounds any particle that has a charge Q 1 with SI units of coulombs. 3.The strength of the electric field at distance r from charge Q 1 is, directed away from a positive charge or else toward a negative charge, where is called Coulomb’s constant. 4. For example, the field at r = 2 meters from a charge Q 1 = + 10 –3 coulomb points away from that charge with Electric Field (denoted by E) Electric field lines E field around an isolated positive charge E field around an isolated negative charge

17. 17 5.The electric field E at distance r from charge Q 1 exerts a force F on another charge Q 2 by Coulomb’s Law: 6.Charges with like signs (+ and +, or else – and –) repel each other, but charges with with opposite signs (+ and –) attract each other. 7.For example, the proton (charge e  1.602  10 –3 C) and the electron (charge – e ) in a hydrogen atom of radius r  10 –10 m attract each other with force (negative forces attract), which holds the electron in orbit around the nucleus. Electric Field (continued)

18. 18 8.The electric field E between two charged surfaces separated by a distance r with a potential difference of V [volts] across an insulator is 9.For example, if V = 10 volts and r = 0.5 meter as shown, then the strength of the electric field is throughout gap (e.g., air between plates). The potential (i.e., voltage) decreases linearly across the gap from left to right. 10. An electric field also surrounds any time-varying magnetic field. Electric Field (continued) + ++ ++++ ++ – –– –––– –– + – 10-volt battery Parallel metal plates (a capacitor) r = 0.5 meter 0 V+10 V

19. 19 1.Danish physicist and chemist Hans Christian Oersted (1777 – 1851) discovered that electric currents create magnetic fields. 2.A magnetic field is a field of force produced by a magnetic object, by an electric current, or by a changing electric field. 3.An electric field is produced by a changing magnetic field. 4.A pure electric field seen by one observer is seen as both an electric field and a magnetic field by a moving observer. Therefore, electric and magnetic fields are two interrelated aspects of a single entity called an electromagnetic field. 5.The north pole of a compass points toward the south pole of Earth’s magnetic field, which is located near the Earth’s geographical north pole. That field is produced by moving charges deep in the spinning Earth’s molten core. Magnetic Field (denoted by B, with a related H field) Compasses reveal the direction of the local magnetic field

20. 20 6.A magnetic field is denoted by B with SI units of and is specified at any point by both a direction and a magnitude. So the magnetic field is a vector field, like the acceleration of gravity and like an electric field. 7.A magnetic field is typically drawn using magnetic field lines, where arrows show the direction of the field and the density of lines indicates its strength. 8.Energy is needed to create a magnetic field, and can be reclaimed when the field collapses, so it can be considered to be “stored” in the magnetic field. Magnetic Field (continued) Iron filings sprinkled on paper above a bar magnet align with magnetic field lines. Arrows on magnetic field lines point from the north pole to the south pole.

21. 21 9.An electric current produces a magnetic field such that the direction of the magnetic field lines is given by the right hand rule as shown below. Magnetic Field (continued) + – Current flow II V 10.In a solenoid (i.e., a coil of wire, which makes an inductor), the total magnetic field is the sum of the magnetic fields from each turn of wire. Making the core out of magnetic material concentrates the field in that core. 11.A magnetic monopole is a hypothetical particle that has only one magnetic pole (either a north pole or a south pole), analogous to an electric charge. 12.In quantum physics, an electromagnetic field is understood to be propagated by force-carrying photons which act as particles and as waves.

22. 22 Web Applets to Simulate Electric and Magnetic Experiments http://phet.colorado.edu/en/simulations/category/physics/electricity-magnets-and-circuits These excellent applets from the University of Colorado at Boulder’s PhET project interactively simulate a variety of experiments with electric and magnetic fields. 1. “Faraday’s Electromagnetic Lab” This excellent applet includes interactive simulations of  A bar magnet with a compass  A pickup coil with a bar magnet and a light  An electromagnet with a compass  A transformer  A generator driven by a water wheel, with a compass and a light 2.“Electric Field of Dreams”  Create an electric field and see how it forces a charged particle to move 3.“Circuit Construction Kit (AC+DC), Virtual Lab”  Build and test your own circuits

23. 23 Early Physicists for the Theory of Electromagnetism Karl Friedrich Gauss 1777 – 1855 André-Marie Ampère 1775 – 1836 Michael Faraday 1791 – 1867 James Clerk Maxwell 1831 – 1879 Maxwell synthesized all previously unrelated observations, experiments, and equations about electricity, magnetism, and optics in a consistent theory. Electricity, magnetism, and light are all electromagnetic fields!

24. 24 The Basic Equations of Electromagnetism (Maxwell’s Equations) NameEquationDescribes Gauss’s law for electricity Charge and the electric field Gauss’s law for magnetism The magnetic field (no magnetic monopole) Ampère’s law (as extended by Maxwell) The magnetic effect of a changing electric field or of a current Faraday’s law of induction The electrical effect of a changing magnetic field

25. 25 Web Applets to Interactively Simulate Electronic Circuits 1.http://www.walter-fendt.de/ph14e/osccirc.htmhttp://www.walter-fendt.de/ph14e/osccirc.htm This applet simulates a simple undamped oscillator circuit with only an inductor (L), a capacitor (C), a battery, and a switch. 2.http://www.falstad.com/circuit/http://www.falstad.com/circuit/ This excellent applet simulates very many types of electronic circuits, and the index includes verbal descriptions of how the circuits work. Included are:  Basics (Ohm’s Law, resistors,  Alternating current (AC) circuits capacitors, inductors,...);(response varies with frequency);  Passive filters;  3-Way and 4-way switches;  Transformers (step-up, step-down);  Diodes (rectifiers and zener diodes);  Operational amplifiers (invert,  Transistors (bipolar, CMOS, differentiate, integrate, oscillate);MOSFET);  Logic gates (AND, OR, NOT,...);  Combinatorial logic (XOR, adder, …);  Sequential logic (flip-flop, counter);  555 timer integrated circuit (chip);  Transmission lines;  Spark gaps