Electric Charge Electric Charge & & Current Current Chapter 20 Chapter 20
Dec 13, 2015
Types of Electric ChargeTypes of Electric Charge What are the two types of charge?What are the two types of charge?
PositivePositive NegativeNegative Ben Franklin named these charges.Ben Franklin named these charges.
Where do these charges come from?Where do these charges come from? ProtonsProtons ElectronsElectrons
Electric FieldElectric Field
Region around a charged particle Region around a charged particle where a force is exertedwhere a force is exerted..
Similar to magnetic fieldSimilar to magnetic field Draw with lines to show what kind of force Draw with lines to show what kind of force
would be on a test charge (always +)would be on a test charge (always +)
Remember, what is a force?Remember, what is a force?
Static ChargeStatic Charge
What is the charge of most objects?What is the charge of most objects?
Trick question??Trick question??
Most objects are neutral.Most objects are neutral. What does that mean?What does that mean?
Protons equal Electrons or Protons equal Electrons or + = -+ = -
So, how do things become So, how do things become charged?charged?
Can all materials become charged?Can all materials become charged? Insulators: electrons cannot be lost easilyInsulators: electrons cannot be lost easily Conductors: electrons free to moveConductors: electrons free to move
Electrons can be lost or gained.Electrons can be lost or gained. Less electrons means…Less electrons means…
Less negative or a overall positive chargeLess negative or a overall positive charge
More electrons means…More electrons means… More negative or a overall negative chargeMore negative or a overall negative charge
Static ElectricityStatic Electricity
A buildup of charges on an A buildup of charges on an object is called Static object is called Static Electricity.Electricity.
Charges buildup but do not Charges buildup but do not flow.flow.
Transferring ChargeTransferring Charge
1.1. ConductionConductionCharge transfer through direct Charge transfer through direct contactcontact
2. 2. InductionInductionMovement of electrons to one Movement of electrons to one part of an object caused by the part of an object caused by the electric field of another objectelectric field of another object
Conservation of ChargeConservation of Charge Charges (electrons) are not created or Charges (electrons) are not created or
destroyeddestroyed So, if one object gains electrons So, if one object gains electrons
another object must have lost another object must have lost electronselectrons
And, if one object loses electrons And, if one object loses electrons another object must have gained another object must have gained electronselectrons
Static ClingStatic Cling
Why does your sock stick to your shirt?Why does your sock stick to your shirt?
Its all about charges, opposites Its all about charges, opposites attract.attract.
Why does a dryer sheet help reduce Why does a dryer sheet help reduce this?this?
When might static cling be When might static cling be beneficial?beneficial?
Static DischargeStatic Discharge
When a negatively charged object When a negatively charged object and a positively object are brought and a positively object are brought together, electrons move until both together, electrons move until both objects have the same charge.objects have the same charge.
The loss of static electricity as electric The loss of static electricity as electric charges move off an object is called charges move off an object is called static discharge.static discharge.
How can static discharge?How can static discharge?
HumidityHumidity Water in the air can pick up charge that has Water in the air can pick up charge that has
built up on an object.built up on an object. SparksSparks
Shock, electrons moving from hand to door Shock, electrons moving from hand to door knob results in neutral objects again.knob results in neutral objects again.
LightningLightning Electrons buildup on clouds then discharge to Electrons buildup on clouds then discharge to
areas of positive charge.areas of positive charge.
Detecting ChargeDetecting Charge Electric charge is invisible, but it Electric charge is invisible, but it
can be detected by a special can be detected by a special instrument called a instrument called a ElectroscopeElectroscope..
Uncharged: metal leaves hang Uncharged: metal leaves hang straightstraight
Charged: metal leaves repelCharged: metal leaves repel
Electrical PotentialElectrical Potential An object will move from a place of An object will move from a place of
high potential energy to a place of low high potential energy to a place of low potential energy.potential energy.
What would be an example of this?What would be an example of this? Electrons will also move from high Electrons will also move from high
potential to low potential energy potential to low potential energy exerted by an electric field.exerted by an electric field.
Potential energy per unit of charge is Potential energy per unit of charge is called electrical potential.called electrical potential.
VoltageVoltage
The difference in electrical potential The difference in electrical potential between two places is called the potential between two places is called the potential difference.difference.
This provides the force that pushes the This provides the force that pushes the charge through a circuit.charge through a circuit.
Voltage is the unit for electrical difference.Voltage is the unit for electrical difference. Voltage causes current to flow through an Voltage causes current to flow through an
electric circuit.electric circuit.
Voltage SourcesVoltage Sources
Creates a potential difference.Creates a potential difference.
Batteries and generatorsBatteries and generators
Just as an increase in the difference in Just as an increase in the difference in height causes a greater flow of water, an height causes a greater flow of water, an increase in voltage causes a greater flow increase in voltage causes a greater flow of electric current.of electric current.
ResistanceResistance Opposition to the flow of charge.Opposition to the flow of charge. Depends on the type of wire, thickness, Depends on the type of wire, thickness,
and length.and length.
Current depends on resistance.Current depends on resistance. The greater the resistance, the less The greater the resistance, the less
current there is for a given voltage.current there is for a given voltage. Path of least resistancePath of least resistance
Ohm’s LawOhm’s Law
Voltmeter: measures potential Voltmeter: measures potential differencedifference
Ammeter: measures currentAmmeter: measures current Ohm’s Law:Ohm’s Law: V=IRV=IR
Voltage=Current x Voltage=Current x ResistanceResistanceVolts=Amps x OhmsVolts=Amps x Ohms
Series CircuitsSeries Circuits
Only one path for the current to takeOnly one path for the current to take
All parts of circuit connected one after All parts of circuit connected one after the other.the other.
Added resistors (light bulbs) Added resistors (light bulbs) decreases currentdecreases current
Ammeter connected in series.Ammeter connected in series.
Parallel CircuitParallel Circuit
Several pathways for current to flowSeveral pathways for current to flow
Each resistor connect to energy Each resistor connect to energy source separately source separately
Each pathway can have different Each pathway can have different current going through itcurrent going through it
Voltmeter is connected in parallelVoltmeter is connected in parallel
Household CircuitsHousehold Circuits
Would you want your house to be series or Would you want your house to be series or parallel?parallel?
Why?Why?
Becoming Part of a CircuitBecoming Part of a Circuit
Short circuit: a connection that allows Short circuit: a connection that allows current to flow through an unintended pathcurrent to flow through an unintended path
Exposed WiresExposed Wires
Resisting CurrentResisting Current
GroundingGrounding
Third ProngThird Prong
Lightning RodsLightning Rods A lightning rod is connected to a grounding A lightning rod is connected to a grounding
wire. When lightning strikes the rod, charges wire. When lightning strikes the rod, charges flow through the rod, into the wire, and then flow through the rod, into the wire, and then into Earth.into Earth.
Fuses & Circuit BreakersFuses & Circuit Breakers
In order to prevent circuits from In order to prevent circuits from overheating, devices called fuses and overheating, devices called fuses and circuit breakers are added to circuits.circuit breakers are added to circuits.
A fuse is a device that contains a thin strip A fuse is a device that contains a thin strip of metal that will melt if too much current of metal that will melt if too much current flows through it.flows through it.
A circuit breaker is a safety device that A circuit breaker is a safety device that uses an electromagnet to shut off the uses an electromagnet to shut off the circuit when the current gets too high.circuit when the current gets too high.
Electric ShocksElectric Shocks
Current in the bodyCurrent in the body The severity of an electric shock depends on The severity of an electric shock depends on
the current.the current. .1 to .2 amps can be dangerous.1 to .2 amps can be dangerous
Resistance in the bodyResistance in the body Dry skin – High resistanceDry skin – High resistance Wet skin – Low resistanceWet skin – Low resistance