Electric Charges

Alittlechemistry  All matter  Atoms are is made up of atoms made of protons, neutrons, and electrons Protons: (+) Neutrons ( no charge ) Electrons: (-)  Atoms can have a positivecharge,a negative charge, or no charge at all.

Charges  Electrical charge – caused by an imbalance of protons and electrons  Positive (more protons than electrons)  Negative (more electrons than protons)  Neutral (same number of protons and (Electric Fields of each shown above…) Opposites attract electrons) Likesrepel

MoreChemistry  A charge can never be created or destroyed. It is transferred from one object to another. This happens to another whenelectronsmovemovefromoneoneobject OppositeCharge Like Charg e

Transferring Charge Electric energy is never created or destroyed, only transferred  Objects (generally those that are can become charged by one of 3 1. Induction 2. Conduction 3. Friction conductors) ways: 

Transferring Charge Induction – Transferring a charge by bringing a charged object NEAR a neutral object without touching it.  The total charge on the door knob will still be neutral, but the opposite sides will have opposite charges

Transferring Charges Conduction - Electrons are transferred from one object to another by contact, or touching.  When a negatively charged rod touches a neutral door knob, electrons transfer from the rod to the doorknob to give the doorknob a negative charge

Transferring Charge Friction - two objects rub up against each other, leaving electrons built up on one side. Both objects become charged. i.e. rubbing a balloon on your head, walking across carpet, wool rubbing on metal… 

Static Discharge  John Travoltage!! phet.colorado.edu/en/simulation/travoltage

Controlling the Path of Electric Charge Electrical Conductor: a material in which  charges move freely i.e. metal (wires) and water  Electrical Insulator: a material in which  charges cannot move freely i.e. plastic, wood, glass, foam, cloth, ceramic 

Controlling the Path of ElectricCharge Electrical Conductor: the metal inside the cord presentsa path of little resistance charge to flow for thefor the Electrical Insulator: the rubber/plastic has a high resistance, to keep the charge from leaving the metal path of wire (and to ensure you don’t shock yourself when you touch the cord!)

CURRENTS AND OHM’S LAW

What?  Electricity – flow of electric current  Electric current –themovementofanan electrical charge.  In most cases, we think of an electric current running through a circuit.  In comes Ohm’s Law.

Ohm’s Law V = I x R V = Voltage (units are volts, v) I = Current (units are ampres, A) R = Resistance (units are ohms, Ω)

Voltage  Voltage is the difference in between two places where  A negative charge (electron) from other negative charges electrical potential electrons are flowing. wants to move away (other electrons.) These repulsive forces increase as electrons are closer to each other. Electrons flow from high potential energy to low potential. This potential difference is usually just called voltage  Voltage provides the energy that pushes and pulls electrons through the circuit.  Voltage is measured in Volts (V)

Batteries  Batteries can have different voltage, and therefore push different strength currents  Range from 1.5 volts to 12 volts  Batteries have a positive terminal and a negative terminal.  Electrons are pushed from the negative terminal and are pulled towards the positive terminal  BUT current is in the opposite direction

Voltage  Basically…  Voltage is difference motion  Voltage is potentialelectrical that sets a charge in the PUSH and is measured in Volts (V)

Current: General Idea  An object moving in a specific direction  Current can be water, air, cars, or charge  Current is caused because of a difference pressure on either side of an object in  Once the difference in pressure is gone, current stops  Pumps & Batteries are used to maintain a difference in pressure.

ElectricCurrent  Just as water current is flow of water molecules, electric current is the flow of electric charge.  Measured in Amperes (A)  In metal circuits, moving flow of charge.  Electrons travel negative to positive  Current travels in electronsmakemakeupthe the OPPOSITE as electrons do. direction

Types of Current THERE ARE TWO TYPES OF CURRENT: In a direct current (DC) the current always moves terminal to the other in the same direction. - example: battery fromone In an alternating current (AC) the current will always alternate directions at regular intervals. - example: appliances at home Remember, direction of the current is opposite the direction of electron flow.

VoltageandCurrent  Voltage PUSHES charges through circuits.  Current is how fast electrons FLOW thru the  Example – you could say that… circuit  Amps measure how much water comes out ofa hose.  Volts measure how hard the water hose. comesoutofa  Basically: As Voltage Increases, Current Increases!

Practice! So how does this relate to awesome computer simulations?

Resistance (R)  Objects use different amount of power because they have different amounts of current running through them.  The difference in current is due to the resistance.

Resistance (R)  Resistance: the tendency for a material to oppose the flow of electrons, changing electrical energy into thermal energy and light.  Resistance movement is caused by internal friction, which slows the of charges through a conducting material.  Resistanceis measured in Ohms (Ω).

Resistance and Wires…  Conductors have low resistance  The better the conductor, the better that electrons will move through the material in the field ie: metal wires presenceofanelectric  Insulators have high resistance  The better the insulator, the more that the substance will resist the movement of electrons. ie:plastic or rubber

Resistance (R)  The resistance of a light bulb filament determines how bright the bulb will be  The filament of a 40watt bulb has a much higher resistance than a 100watt bulb This is because more resistance = less current = dimmer bulb So being able to control resistance would be agood thing… a wire:  2 ways  make that we can increase resistance in the wire longer (ie: the loops) wire thinner Thicker wire = less resistance Thin wire = more resistance

Ohm’s Law V = I x R V = Voltage (units are volts, v) I = Current (units are ampres, A) R = Resistance (units are ohms, Ω)

Practice! The headlights of a typical car are powered by a 12V battery.What is the resistance of the headlightsif they draw 3.0 A of currentwhenturnedon? Use your Ohm’s Law Triangle Insert your values Use units Solve!

SERIES AND PARALLEL CIRCUITS

Circuits  Provides a path for electricity to travel  Similar to water pipes in your  Because of the voltage of an will travel through the circuit house outlet, electrons  Electrons NEED to travel around the ENTIRE path for anything to work

Open vs.Closed Circuits  When there is closed circuit.  When there is a complete path, the circuit is considereda NOT a completepath,thecircuitis consideredanopencircuit.  A switch allows you to openand close a circuit

Conductive Ink!!!  The ink on this page conducts electricity ink). (yes, it is special  What over?  … happens to thewhenthepagepageisfolded toto thethe circuit? lightbulb? current?

Safety Precautions  If too many devices (tv, radio, hair connected to an outlet, the overall circuit is lowered  This increases the current traveling dryer, etc) are resistance of the through the circuit, possibly more than a safe level  This is called an overloaded circuit. ofcurrent.  Too much current traveling though a wire can cause fires.

when too Safety Precautions  Both of these objects open the circuit by disrupting the complete circle, preventing damage to the rest of the circuit.  FUSE – a ribbon of metal wire thatmelts much current flows through  If current becomes too high, the fuse melts, and the circuit is open  Can only be used once then must be replaced it

Safety Precautions  Circuit Breaker opens a circuit with a high current  Uses an electromagnet that responds to current overload by opening the circuit Basically it is magnetic switch that ‗trips‘ The circuit breaker acts as a switch.  Can be used multiple times. reset once ―tripped. Must be

CircuitDiagrams  Uses symbols to represent parts of a circuit  Shorthand way todescribe a realcircuit

CircuitSymbols:HowHowtoDraw On–OffSwitch ElectricalSupply (Battery) Resistor LightBulb Remember, the circuitdrawing needs to be a COMPLETEpath.

CircuitSymbols:HowHowtoDraw

You trytotodrawsomecircuits: A circuit switch. withoneresistor, one battery,andone 1. A circuitwithwithtwotworesistors, three batteries, and 2. one switch.

Circuits: 2 Diff Types  Caneitherbeseriesorparallel. Series:1 pathParallel: 2+ Paths

Resistance (Ω) Overview: Seriesv Parallel Circuits MUST CALCULATE (Voltage drops to 0v after Series Parallel Pathways for electrons and current Only 1 path.Multiple Pathways for current Current (I) Always the same throughout Different at each branch – Voltage (V) VOLTAGE DROP after every resistor/bulb: MUST CALCULATE each separately Each Branch starts with same voltage each branch) Add up all to get total Each branch different - MUST CALCULATE each branch

Let‘s Practice: Identify WS…

Try some drawings!  1) Series: with 2 resistors (one is 4 ohm, 12V battery, and a 10 ohm light bulb. one is 7ohm), a  2) Parallel: with a 1.5 volt battery and 3 light bulbs (each on its own branch). Light bulbs have a resistance of2, 4, and 6 ohms.  3)Series: 6v battery, one switch, one 20ohm resistor.  4)Parallel: 12volt battery, 3 light bulbs.2 light bulbs (2 3 rd and 3 ohms) are on one branch, while the (8ohms) is on another branch) light bulb

Circuits: 2 Diff Types  Caneitherbeseriesorparallel. Series:1 pathParallel: 2+ Paths

Series circuits  There is only 1 path for current/electrons to travel  If the circuit opens in any way, the whole circuits stops working because current STOPS.

Series Circuits  Current only takes one path for electrons  Ifyou remove a light bulb or one burns out — the ENTIRE circuit stops working!  Current stays the same as it flows through every part ofthe circuit  Resistance (and therefore voltage), will change at different points on a series circuit

Current in Series  Current is the same at all points  Electric current always FLOWS from positive (+) to negative (-)  Which is OPPOSITE the flow of electrons.  Use Ohm‘s Law to find current using total resistance and voltage

ResistanceinSeries  Add up all resistors to get totalresistance  Current MUST go through each resistor in series because there is only one path.

Voltage Series  Voltage “drops” after each resistor has been passed.  Calculate voltage drop by calculating voltage at each resistor  V = I*R  V = (current * resistor)

Sample Problem #1 Draw a series circuit with a 3 different1.5 batteries (all together), 2 equal resistors, and a current of 0.5 A. V  What is 3 * 1.5 What is V = IR What is the total voltage of the circuit? volts = 4.5 volts 1. thetotal resistance of the circuit? v / 0.5A=9ohms theresistance of each resistor? 3. 9ohms / 2 equal resistors=4.5 ohms each

Sample Problem #2 What is the total resistance of the circuit? 17ohms + 12ohms + 11ohms = 40 ohms   What is V = IR the  the current for the circuit? 60 volts / 40ohms = 1.5amps   Whatisvoltage drop across V 1 = IR V 1 = 1.5a * 17ohm V 1 = 25.5v each resistor?  V 3 = IR V 3 = 1.5a * 12ohm V 3 = 18v V 2 = IR V 2 = 1.5a * 11ohm V 2 = 16.5v

Parallel Circuits  Have more than one path for current to flow  Paths are also known as branches  If you remove a resistor, the other branches still work

Voltage in Parallel  Voltage is the same across each branch  because each branch is on the same wire  Voltage will drop to after each branch. 0v0v But we won‘t calculate that…

Current in Parallel  Current depends on resistance in each branch  The current in each branch will be different if the resistors have different values  It one branch has less resistance, more charge will move through it because that bulb offers less opposition to the movement of current.  The sum of the currents on each of the MUST equal the total starting current branches  EACH BRANCH is calculated using Ohm‘s Law

Practice problem #3  Draw a parallel circuit with two resistors, one 2 ohm and one 3 ohm (one on each branch) and a 12 V battery. What is the 12 volts voltage through each resistor? 1. What is V = IR What is thecurrent flowing through each branch? 2. 12v/2ohms = 6v total current? 12v/3ohm = 4v the 3. 6v + 4v = 10v

Overview:SeriesvParallelCircuits MUST CALCULATE (Voltage drops to 0v after SeriesParallel Pathways for electrons and current Only 1 path.Multiple Pathways for current Current (I) Always the same throughout Different at each branch – Voltage (V) VOLTAGE DROP after every resistor/bulb: MUST CALCULATE each separately Each Branch starts with same voltage each branch) Add up all to get total Each branch different - MUST CALCULATE each branch

Magnets A magnet is an object that produces a magnetic field. Magnets can be natural or man made The only natural metals that are naturally magnetized (and can become magnetized) are Nickel, Iron, Cobalt, and Gadolinium. If they are made, they are formed from things that are naturally magnetic.

Magnetic Poles All magnets have 2 poles: North and South Laws of attraction still applies Like poles repel, opposite poles attract If a magnet is cut, each piece will still have two poles

Permanent Magnets Substances that are magnetic all the time Can change anything into a magnet by rubbing a permanent magnet over it several times Permanent magnets can have magnetic properties but not always be a magnet (ex: iron) Permanent magnets can last for minutes, or forever

Magnetic Fields When magnets repel or attract each other it’s because of their magnetic fields Magnetic field – region where a magnetic force can be detected

Magnetic Fields Below: Iron filings placed over a magnet align with the magnetic field of the magnet

Magnetism and Electric Currents Electric currents produce magnetic fields Magnetism is produced by moving electric charges The magnetic field of a coil of wire resembles that of a bar magnet

Electromagnets A strong magnet created when an iron core is inserted into the center current-carrying coil of wire Strength depends on: Thicker wire Thicker wire = less resistance the number of loops in the wire More loops = stronger the amount of current More current = stronger ofa And remember, more voltage means more current size of the iron core Bigger core = stronger

Electromagnets So why are electromagnets useful? Can turn them on / off  Cutting the current off turns off the magnet Can control their strength Just like we talked about last slide. More current and voltage Bigger Iron core More coils around the iron core

Motors Electric motors change electrical energy to mechanical energy Done by running an electric current make an electromagnet. throughcoilstoto When the electric current runs through the armature, it becomes magnetized The armature spins because motors use other magnets to push and pull the armature and create motion.

Generators Change mechanical energy into electric energy Done by moving a coil past a magnetic field. Use electromagnetic induction to produce an electric current. When a coil of wire moves through a magnetic field an electric current can be produced. This is electromagnetic induction. Produces AC current.