Chapter 3 - Electrical Properties Chapter 4 - Electrical Quantities

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

Atoms The smallest particle of an element that retains the characteristics of that element. Each atom has a unique and specific number of electrons surrounding the nucleus. This is what makes each element different.

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

Electron shells There can be as many as 7 shells / orbits Shell Number Number of Electrons in that shell 50 32 18 8 2 n =1

Number of electrons in each shell Shell Number = n Number of electrons in that shell = 2n2 1 2(1)2 = 2 2 2(2)2 = 8 3 2(3)2 = 18 4 2(4)2 = 32 5 2(5)2 = 50 6 2(6)2 = 72 7 2(7)2 = 98

Each shell is split up into Subshells .

Valence Electrons The valence electron is the number of electrons in the outermost shell of an atom. (Not sub-shell) http://au.answers.yahoo.com/question/index?qid=20080327135829AA6jdpj Valence electrons may be easy or hard to be freed. Atoms tend to want to be neutral.

Atoms tend to want to have exactly 8 valence electrons Bonding occurs to facilitate this Current is possible because of this Note: Although it looks as though there are way more than 8 electrons in the 3rd shell, which makes it seem that it is possible to have more than 8 valence electrons, the order in which the shells are filled is not sequential. See video on next page for more info.

Number of Valence Electrons Max number of valence electrons is 8 1 8 2 Transition metals 3 4 5 6 7 2 2 2 2 2 2 2 2 2 2 See this video for an explanation of why transition metals all have 2 valence electrons https://www.youtube.com/watch?v=1TZA171yxY4&feature=youtu.be

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

Semiconductors Conductivity increases with increasing temperature This is opposite of metal Useful properties Can pass current more easily in one direction than the other, Variable resistance Sensitivity to light or heat. Conductivity can be modified by adding impure atoms (atoms that are not purely semiconductive)

1 Coulomb is like a large group of electrons Coulomb Units 1 Coulomb is like a large group of electrons 6.24x1018 electrons = 6,240,000,000,000,000,000 electrons 1 amp = 1 Coulomb/sec So how many Coulomb’s is 1 electron??? 1.6 x 10-19 C = .00000000000000000016 C

Resistive Constants

Random video of the day http://www.pbs.org/video/2365946487/ http://www.pbs.org/video/2365946487/  Start at 28 min to 29min If it doesn’t show up, search “Search for the Super Battery” by PBS

Random Video of the Day

B * C A F = D2 A = 2 B = 3 C = 4 D = 2 F = ?

Coulomb’s Law of Charges 1 Coulomb is like a large group of electrons 6.25x10^18 electrons So how many Coulomb’s is 1 electron??? 1.6 x 10-19 C 𝐹=𝑘 𝑞 1 𝑞 2 𝐷 2 Relational Force between particles F = force in Newtons = ? = 0.4mC 56nC = 5mm q1, q2 = the charges in coulomb units k = Coulomb’s constant = 8.988x109 d = distance in meters between charges d - Can also be imagined as the area in the electric field Force = 8053 Newtons

How would you solve for D? 𝐹=𝑘 𝑞 1 𝑞 2 𝐷 2

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

Reminder of Tardys

Chapter 4 – Electrical Properties What is Current? What is Voltage? What is Resistance?

Voltage, current & resistance analogy -

Introduction Video http://www.youtube.com/watch?v=EJeAuQ7pkpc&feature=fvw

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.

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.

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

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

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.

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

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.

Kinetic vs Potential Energy Kinetic Energy 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!

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

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

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

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.

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?

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… -

Another RVOTD https://www.youtube.com/watch?v=FGoaXZwFlJ4

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

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.

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

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

Schematic Symbols (pg 59 of book)

Breadboarding Basics What is a Breadboard?

What the purpose of a breadboard?

What circuit are we going to breadboard today?

Show large breadboard

How to use a breadboard

How does a breadboard work?

Are these wires connected?

Which is Correct???

You can also connect Integrated Circuits (IC’s)

LAB http://www.youtube.com/watch?v=oiqNaSPTI7w Intro to breadboard

Questions Why is the protoboard sometimes referred to as a breadboard? What is the purpose of the bus strips? What is the purpose of the recessed center divider? How would you connect 15 components together? Make sure to read discussion