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Lecture 3

Lecture 3. Chapter 3 - Electrical Properties Chapter 4 - Electrical Quantities. Making Molecules with Atoms http :// www.youtube.com/watch?v=qmgE0w6E6ZI ok. Elements and Compounds. Element - a substance that cannot be reduced to a simpler substance by chemical means

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Lecture 3

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  1. Lecture 3 Chapter 3 - Electrical Properties Chapter 4 - Electrical Quantities

  2. Making Molecules with Atoms • http://www.youtube.com/watch?v=qmgE0w6E6ZI • ok

  3. Elements and Compounds • Element - a substance that cannot be reduced to a simpler substance by chemical means • ie: iron, gold, silver...

  4. Atoms • The smallest particle of an element that retains the characteristics of that element. • Atoms are like letters, molecules are like words • ie: the water molecule

  5. Electrons vs. Protons • Electrons are negatively charged (-) • Protons are positively charged (+) • Electrons and protons attract each other

  6. Atomic Number • Atomic Number is the number of protons in its nucleus

  7. Electron orbits • Electrons can only “jump” orbits or shells in steps The number of electrons in any particular orbit follows the equation: # Electrons = 2n2 n = orbit number

  8. How many shells would the electrons in the silver atom fill? Electron Orbits • There can be as many as 7 shells in an atom • K, L, M, N, O, P, and Q • How many electrons, if full, would be in 7th shell?

  9. Sub-shells of Orbits • Each Orbit (K, L, M, N, O, P, and Q) • has sub-shells (s, p, d, f, g) • How many electrons in Orbit N • sub-shell f? 14 http://en.wikipedia.org/wiki/Electron_shell

  10. Subshell 1 Subshell 2 Subshell 3 Subshell 4 Subshell 5 Orbit 1 Orbit 2 Orbit 3 Orbit 4 Orbit 5 . . .

  11. Valence Electrons • The valence electron is the number of electrons in the outermost sub-shell of an atom. • Valence electrons may be easy or hard to be freed. Atoms tend to want to be neutral.

  12. How many valence electrons in silver? 1

  13. How many valence electrons in silver? 1

  14. How many valence electrons in gold? 1

  15. How many valence electrons in aluminum? 3

  16. Conductors vs. Insulators • Conductors usually have 3 or less valence electrons. Why? • Insulators usually have 5 or more valence electrons. • Semiconductors? • How many valence electrons • Definition • Best Conductors: • Silver • Copper • Gold • Aluminum • Good Insulators • Rubber • Plastic • Glass • Common semiconductors • Germanium • Silicon

  17. Resistive Constants

  18. Static Electricity • Shielding wire • EMI (ElectroMagetic Interference) • Grounding

  19. Ionization • Positive vs Negative ions

  20. Random Video of the Day

  21. A F = R2 B * C A = 2 B = 3 C = 4 R = 2 F = ?

  22. Coulomb’s Law of Charges 1 Coulomb is like a large group of electrons 6.25x10^18 electrons • Relational Force between particles So how many Coulomb’s is 1 electron??? 1.6 x 10-19 C F = force in Newtons = ? = .4mC 56nC = 5mm q1, q2 = the charges in coulomb units ke = constant = 8.988x109 Answer 8053 N r = distance in meters between charges r - Can also be imagined as the area in the electric field

  23. More Coulomb’s Law practice problems...(aka worksheet)

  24. Chapter 4 – Electrical Properties • What is Current? • What is Voltage? • What is Resistance?

  25. Kinetic Energy Potential Energy Kinetic vs Potential Energy The energy of a particle or system of particles derived from position, or condition, rather than motion. The energy possessed by a body because of its motion ie: a roller coaster, a moving car ie: a stretched rubber band, a coiled spring. In our case, a BATTERY!

  26. Introduction Video

  27. Current • Current is a movement of charged particles • Within metal conductors, the charged particles that are moving are electrons. • These electrons flow when there is a potential difference in the charges across a conductor. Aka: protons are on the other side.

  28. Current – electron flow model • The current you are used to working with is nothing more than moving electrons, moving from a region of negative charge to an area of positive charge. • As a potential difference is impressed across the conductor, the positive terminal of the battery attracts electrons beyond point A. Point A becomes positive because it now has an electron deficiency. As a result, electrons are attracted from point B … and so on. • This is true for metal conductors.

  29. Current – Conventional current flow • If you Google “current” or look in a friends electrical engineering book, you might find that current flows from positive to negative. • A few perspectives on this include: • Currents of positive ions • Hole Charge Current in p-type semiconductors • Arrows shown on diodes and transistors are for current, not electron flow

  30. Electron Flow vs. Conventional Current Flow Conventional Current Flow Electron Flow + - + - • Which one do we use??? • Electron Flow • However I will still call it current. 

  31. Current Magnitude • If the potential difference is increased, the electric field is stronger, the amount of energy imparted to a valence electron is greater, and the magnitude of current is increased.

  32. Current Magnitude • If 6.25 x 1018 electrons pass a given point in one second, then this is called one amp. Q t electrons second Coulomb second = 1 Amp 6.25 x 1018 I = = 1

  33. Voltage • So what causes there to be a potential difference in charges across a conductor? • (how do you get protons to be stored on one side and electrons on the other?) • There are 6 ways this can be done, and this is part of your homework to look up.

  34. Voltage • Voltage is also known as • Electromotive Force (EMF) • Usually associated with the voltage a battery makes • Potential difference • Difference in charges

  35. Voltage Example • How much voltage is produced when you shock someone? • When you feel it: 2,000 V • When you see it: 8,000 V • Maximum spark: 25,000 V

  36. Other Voltage Examples • AA, AAA, C, D batteries: 1.5 V • Car Battery: 12V • Cell Phone Battery: 3.7 V – 4 V • Watch Battery: 3V • Your Computer?: 5V

  37. Voltage in a battery • Just like a rubber band that has been stretched, there is potential for it to do work when released. • This is similar to the storage of voltage in a battery • Batteries only have a certain amount of charge stored before they run out.

  38. Voltage is Relative • Clapping example • Without a reference point, a voltage of 12V is meaningless. • The reference point for voltage most of the time is ground, or 0V. • However, there are different types of grounds. How is an airplane grounded?

  39. Voltage is Relative (cont.) + • For example, what is the voltage at this point, if each battery is 1.5V? • Depends, if its referenced to: • Ground • Negative side of same battery • Top of battery above… -

  40. Resistance • Resistance is an opposition to current flow • Resistance can be made by: • Varying the type of material, (think valence electrons) • Varying the length of material • Varying the amount or cross-section of material • Resistors are like poor conductors. The are somewhere between a conductor and an insulator

  41. Resistors (cont.) • Resistors are a little like transducers in that they convert electrical energy into heat. • Voltage is converted into heat when electrons bump into each other so voltage is lost.

  42. What is the opposite of resistance? • Conductance 1 R Measured in Siemens [S] G =

  43. Voltage, current & resistance analogy - - - - - - - - - - - -

  44. A practical Electric Circuit Below is a schematic diagram of a flashlight.

  45. Schematic Symbols (pg 59 of book)

  46. LAB

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