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February 25, 2009 Notes Electricity CW Static Electricity Pre-Lab HW Electricity and Subatomic particles

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Electricity Chapter 11

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11.1 Electric Charge Basic facts about the atom Matter is made of atoms ParticleLocationCharge ProtonNucleus(+) NeutronNucleusnone ElectronCloud(-)

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Model of a Helium atom If a helium atoms has 2 protons 2 neutrons 2 electrons

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The Fundamentals Atoms consist of a small, densely packed, (+) nucleus (p+ & n) Surrounded by a (-) cloud (e-)

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The Fundamentals Mass of a p+ = 1 amu (atomic mass unit) 1 amu = 1.66 x 10 -27 kg! Also refered to as u Mass of a n = 1amu Mass of an e- = 0! Therefore the nucleus contains the entire mass of the atom! The mass of the electrons is negligible!

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The Fundamentals Electron cloud has order to it! Electrons are arranged in orbitals. Orbitals radiate out from the nucleus

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The Fundamentals Atoms in their normal state are neutral # p+ = # e- # p+ determines the identity of the element ( Atomic Number on periodic table)periodic table Atoms can ONLY gain or lose e-! NEVER PROTONS.

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The Fundamentals Ion atom with a charge. Gain 1 or more e- = negatively charged ion = ANION (# + < # -) Only non-metals do this! Lose 1 or more e- = positively charged ion = CATION Only metals do this!

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Law of Conservation of Charge: Charges are neither created nor destroyed THEY ARE MOVED! e- transferred from one object to another. (e- never appear or disappear) Ex: by rubbing two objects together Static electricity accumulation of a charge

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Properties of sub-atomic particles Like charges repel! (p+ p+) (e- e-) Opposite charges attract! (e- p+) Atoms only lose or gain electrons within their outermost orbital. Why?

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14 TriboElectric Series list that ranks various materials according to their tendency to gain or lose electrons VERY POSITIVE looses electrons Human hands (usually too moist though ) Rabbit Fur Glass Human hair Nylon Wool Silk Aluminum Paper Cotton Do these look familiar to you? Which is a conductor? Insulator?? VERY NEGATIVE gains electrons Teflon Vinyl Scotch Tape Saran Wrap Styrofoam Polyester fabric Gold/Platinum/Brass/Silver/Copper Hard Rubber Amber Wood

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Agenda 26-Jan: GET OUT YESTERDAYS HW! Notes Electricity CW/HW Electric Charge & Coulombs Law WS

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Static Electricity & Electric Charge: Charging by Friction transfer of e- by contact. e.g. rubbing your head with a balloon

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Static Electricity & Electric Charge: Charging by Polarization creation of a temporary charge by bringing a charged object near a neutral one. (e- get rearranged in atoms to create partial positive and negative surfaces.)

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Static Electricity & Electric Charge: Polarization

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Static Electricity & Electric Charge: Charging by Induction using one object to charge another.

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Electric Charge: Measured in Coulombs (C) 1 Coulomb represents a HUGE amount of charge! p+ = 1.602 x 10 -19 C e- = -1.602 x 10 -19 C

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Coulombs Law: Relates charge on two objects (q 1 and q 2 ), the distance between their centers (r), and the electrical force (F E ) F E = k x (q 1 x q 2 ) r 2 k = 9 x 10 9 Nm 2 /C 2 How does force change with distance?

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Coulombs Law: The force between two charges acts along a line joining their centers. Charges obey Newtons 3 rd Law of motion they make action- reaction pairs.

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Coulombs Law: If a p+ at a particular distance from a charged particle is repelled with a given force, by how much will the force decrease when the distance between the two is three times greater? Fives times greater? What is the charge on the particle in this case?

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Agenda: March 3rd Notes Electricity Fix yours Finish Review Questions 7-12 on p 188 Exercises 8 16 on p 189 Tomorrow Circuit Lab!

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Electric Current Electric charges, electrons, are always present, but may not be moving! Current the flow of charge, or electrons in one direction, (- ) (+).

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Electric Current Measured in Amperes (Amps, A) 1 Amp = 1 Coulomb per second How many electrons per second is that?

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Electric Current Just like water flows downhill (from high GPE to low), electrons flow from high electrical potential (pressure) to low electrical potential. Voltage (V) a measure of the difference in electrical potential between two parts of a circuit, or the joules of electrical work done per second (Watts) by the current.

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Electric Current Voltage is therefore Watts Amps, or Joules (PE) Coulombs (charge)

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Electric Current Batteries make use of chemical reactions to create a difference in electrical potential energy, or pressure When an e- leaves a battery, it carries E. The e- gives up its E to the electrical device it powers. The e- travels back to the battery to get more E. This cycle continues until all of the chemicals in the battery are used up and the reaction stops.

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Electric Current Conductors: materials through which electrons move easily Metals are good conductors Why? Atoms of metal bond by sharing electrons, and in turn act like 1 huge molecule. Valence electrons (those furthest away from the nucleus) are free to move anywhere.

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Electric Current Insulators: materials through which electrons DO NOT move easily Rubber, glass & wood are good insulators Why? Atoms/molecules of these material stick together through surface area interaction, because the electrons within these atoms of these molecules are fixed within chemical bonds.

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Questions to answer: What power does a 1.5 V battery give to each amp of current in a circuit? What flows when there is an electric current in the wire? Why is it easy to create a current in a conductor and not in an insulator?

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Agenda March 4 th Notes Resistance & Circuits CW Electrical Resistance WS http://www.moourl.com/circuit

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Electrical Resistance Resistance - a measure of how strongly a wire or other substance resists current flowing through it. conductors are low resistance materials, electrical flow is fast insulators are high resistance materials, electrical flow is slow

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Electrical Resistance Total resistance determines Total current. In a circuit each device attached adds to the total resistance in the system. As you increase resistance you decrease current.

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Electrical Resistance You and a friend are trying to illuminate a space that has very poor lighting. You both have several feet of wire, two batteries and several light bulb systems to work with. Your friend strings together three light bulbs in a series. You decide set up a one bulb circuit. Whose set up provides the room with more light?

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Electrical Resistance In a wire... TO decrease resistance use thicker wire lower the temperature decrease the length of the wire TO increase resistance do the opposite of above...

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Electrical Resistance Resistance is measured in OHMS, represented by Greek symbol omega (). We already know that resistance results in current... George Ohm relates current, voltage and resistance... V and I are directly related, and are inversely related to R. OHMS LAW: Current (I) = voltage (V) /resistance (R)

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Electrical Resistance Uses of resistance: Electrical devices utilize resistance to control flow of current through resistors. Specifically, devices are designed with resistors that cause the right amount of current to flow when connected to the proper voltage.

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Electrical Resistance Why can we receive a fatal shock from a wall socket, but handle a 9 V battery safely? Ohms Law... 9V/100,000 (R skin) = 0.00009 amps. We can feel an I of 0.005 amps... Wall sockets provide a V = 120 V 120 V/100,000 ohms = 0.0012 amps. Wet skin has an even lower resistance, because of water's high conductivity... Lower resistance means greater current, which increases the possibility for a fatal electric shock...

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Electrical Resistance Practice (EASY!) How much current will flow through a lamp that has a resistance of 100 ohms when voltage is 25V?

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Electrical Resistance More Practice At 100,000 ohms, how much current will flow through your body if you touch the terminals of a 12 V battery? If your skin is covered with salt water reducing the resistance to 100 ohms, how much current will flow through your body if you touch the terminals of a 12 V battery? Will you feel it?

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Agenda March 5th: Get out HW Notes on Series and Parallel Circuits HW Series and Parallel Circuits

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Electrical Circuits Circuit path along which e- flow. Voltage source battery Conductor wire Device electrical device that changes electrical E to another type of E.

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Electrical Circuits Series Circuit Only one path through which e- flow. (I) is the same at all points in the circuit. If there is a break ANYWHERE in a series circuit, all devices stop.

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Electrical Circuits (I) & (R) in a Series Circuit: R in a series circuit = sum of R for individual devices. R for the wire is TINY so we ignore it R total = R 1 + R 2 + R 3

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Electrical Circuit You try A series circuit contains a 12-V battery and three bulbs with a resistance of 1, 2, 3. What is the current in the circuit?

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Electrical Circuits Devices convert Electrical E to another form of E. As current passes through each device its power is reduced. Remember V = P I, or W per A. If P after each device, then V , too! Voltage drop

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Electrical Circuits Kirchhoffs Law: the sum of all V drops in a system must be equal to the V battery.

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Electrical Circuits You try: A circuit contains a 9-V battery, 1- bulb, and a 2- bulb. Calculate the circuits total R and I. Then find each bulbs voltage drop.

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Electrical Circuits Parallel Circuit More than one path through which e- flow; branch. (I) splits at one or more branches.

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Electrical Circuits (I) & (V) in a Parallel Circuit: Kirchhoffs Law I in a parallel circuit = sum of I for individual branches. I total = I 1 + I 2 + I 3 V is the same in every branch! I in each branch is determined by R in each branch.

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Electrical Circuit Parallel Circuit Ads: Each device has a V drop = V battery. Each device may be turned off independently without affecting other devices in circuit.

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Electrical Circuits Devices decrease resistance in a parallel circuit! More devices = more branches. Remember, I parallel = sum of I per branch. Therefore, more branches = more current.

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Electrical Circuits All of the electrical outlets in Jonahs living room are on one parallel circuit. The circuit breaker cuts off the current if it exceeds 15 A. Will the breaker trip if he uses a light (240 ), stereo (150 ) and an air conditioner (10 )?

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Electrical Circuits Resistance & Electricity: Resistance converts Electrical E to Thermal E Short Circuits = parallel braches are formed with no device (resistance) present. R wire = 0.001 . 1.5 V battery produces an I = 1500 Amps!!

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Electrical Circuits Circuit breaker switch that opens circuit when I gets too great. Fuse piece of metal that melts when I gets too great (openning circuit).

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Agenda Jan-29: Submit HW Notes Electricity HW- SerParallel Circuits Packet Circuits Galore Lab; Test Next Week!

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Electricity & Power Remember that Voltage tells us the amount of electrical power per Amp of current Therefore we can calculate electrical power simply Power = Voltage x Current

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Electricity & Power Electrical Power is the rate at which electrical energy is transferred by a current. Electrical Power is measured in Watts (W) or kilowatts (kW). 1000 Watts = 1 kW

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Electricity & Power A 12-V battery is connected in series to two identical light bulbs. The current in the circuit is 3 A. Calculate the power output of the battery.

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Electricity & Power Buying Electricity: Electricity Companies charge by kWh (kilowatt hours). 1 kWh = 1 kilowatt of Electrical power has been used in 1 hour. kWh are units of Energy, not Power!

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Electricity & Power How much does it cost to run an electric stove for 2 hours if the electric stove using 3000 W per hour, and the electric company charges $0.15 per kWh?

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Electricity & Power Electricity comes from two sources: Batteries Direct Current (DC) current always flows in one direction. Power Plants Alternating Current (AC) direction of current changes (usually 60xs)

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Electricity & Power Distributing Electricity: Household electricity comes from power plants via high tension wires. V = IR. I is VERY BIG, & R is VERY SMALL (R wire tiny). Electrical Power transmitted at a VERY HIGH I prevents Electrical E lost due to R. MOST efficient!

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Electricity & Power Transformers: Voltage of electricity produced at plants to VERY HIGH levels. Voltage of electricity carried by transmission lines closer to your home eventually down to 120 V or 240 V.

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Agenda Jan-30: Submit HW Circuits Galore Lab! HW Part 2: Circuits Galore Lab; Test Next Week!

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Agenda Feb-2: Submit HW Review HW finish study guide; Test Wednesday

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Agenda Feb-3: Submit HW Review Test Tomorrow~