 # Electricity & Magnetism Static Electricity, Electric Fields, Currents, Circuits Magnetic Fields & Electro Magnets Motors & Generators.

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Electricity & Magnetism Static Electricity, Electric Fields, Currents, Circuits Magnetic Fields & Electro Magnets Motors & Generators

Atoms… Have neutrons, protons, and electrons.Have neutrons, protons, and electrons. Protons are positively chargedProtons are positively charged Electrons are negatively chargedElectrons are negatively charged

Electrons… Are located on the outer edges of atoms…they can be moved.Are located on the outer edges of atoms…they can be moved. A concentration of electrons in an atom creates a net negative charge.A concentration of electrons in an atom creates a net negative charge. If electrons are stripped away, the atom becomes positively charged.If electrons are stripped away, the atom becomes positively charged.

+ - + + + + The world is filled with electrical charges: + + + + + - - - - - - - - -

What is this electrical potential called? Static ElectricityStatic Electricity -- - - - - - + + + + +

Static Electricity The build up of an electric charge on the surface of an object.The build up of an electric charge on the surface of an object. The charge builds up but does not flow.The charge builds up but does not flow. Static electricity is potential energy. It does not move. It is stored.Static electricity is potential energy. It does not move. It is stored. Charge is source of all electric force – both attractive and repulsive.Charge is source of all electric force – both attractive and repulsive.

Static Discharge… Occurs when there is a loss of static electricity due to three possible things:Occurs when there is a loss of static electricity due to three possible things: Friction - rubbingFriction - rubbing Conduction – direct contact – charging by conduction is charging by contact.Conduction – direct contact – charging by conduction is charging by contact. Induction – through an electrical field (not direct contact) – charging by proximity.Induction – through an electrical field (not direct contact) – charging by proximity.

Conductors vs. Insulators Conductors – material through which electric current flows easily. Insulators – materials through which electric current cannot move.

Examples Conductors:Conductors: –Metal –Water Insulators: –Styrofoam –Rubber –Plastic –Paper

Ben Franklin Noticed Two types of chargeNoticed Two types of charge Mobile chargeMobile charge Stationary chargeStationary charge Positive electricity – when he rubbed glassPositive electricity – when he rubbed glass Negative electricity – when he rubbed amberNegative electricity – when he rubbed amber

More Ben Electrons move and leave a positive chargeElectrons move and leave a positive charge Charge is caused by the transfer of electronsCharge is caused by the transfer of electrons Ionization energyIonization energy

The Electroscope A device used to detect the presence of electrical chargeA device used to detect the presence of electrical charge It charges by inductionIt charges by induction Cannot tell the type of charge – negative or positiveCannot tell the type of charge – negative or positive

Law of Conservation of Charge The total amount of charge in the universe remains constantThe total amount of charge in the universe remains constant Single charges can be neither created or destroyedSingle charges can be neither created or destroyed Charge is an intrinsic property of protons and electronsCharge is an intrinsic property of protons and electrons

Coulomb’s Law

Action – reaction pairsAction – reaction pairs Unit of charge – Coulomb (C)Unit of charge – Coulomb (C) Distance is measured in metersDistance is measured in meters K = 8.988 X 10 9 Nm 2 /C 2K = 8.988 X 10 9 Nm 2 /C 2 1 e - = 1.609 X 10 -19 C1 e - = 1.609 X 10 -19 C 1 C = 6.25 X 10 18 e -1 C = 6.25 X 10 18 e -

o is the permittivity of free space 8.854 X 10-12 C2/Nm2 Relates to how well a substance allows the presence of a charge

Vector Nature of Electrical Forces Electrostatic forces add vectoriallyElectrostatic forces add vectorially Pythagorean theorem and inverse tan.Pythagorean theorem and inverse tan.

The Electric Field Introduced by Michael FaradayIntroduced by Michael Faraday Similar to a gravitational fieldSimilar to a gravitational field A point charge generates a field around it that has an effect on its environment.A point charge generates a field around it that has an effect on its environment. You can determine the effect on a test charge at any point in the field.You can determine the effect on a test charge at any point in the field.

Uniform Electric Field Between two parallel platesBetween two parallel plates Connected to a source of current – a voltageConnected to a source of current – a voltage Field is uniform throughout the area between the platesField is uniform throughout the area between the plates A way of controlling a field to do work.A way of controlling a field to do work.

Electric Field Intensity (E) Electric force per unit test chargeElectric force per unit test charge Test charge itself is considered small enough to not affect the fieldTest charge itself is considered small enough to not affect the field

The Equation

Electric field is a vector quantity with units, N/C.Electric field is a vector quantity with units, N/C. You can also find the electric field intensity from the magnitude of the point chargeYou can also find the electric field intensity from the magnitude of the point charge Use Coulomb’s lawUse Coulomb’s law

The Equation

Q means “test” chargeQ means “test” charge q means “point” charge q means “point” charge

Electric Potential What causes charges to move? What causes a ball to roll down hill? Why does heat travel from hot to cold?

More Electric Potential Electric potential energy is analogous to mechanical or gravitational potential energy.Electric potential energy is analogous to mechanical or gravitational potential energy. Electrical potential – voltage – allows us to describe physical situations easier in terms of field or charge.Electrical potential – voltage – allows us to describe physical situations easier in terms of field or charge.

What is Voltage? The measure of energy given to the charge flowing in a circuit.The measure of energy given to the charge flowing in a circuit. The greater the voltage, the greater the force or “pressure” that drives the charge through the circuit.The greater the voltage, the greater the force or “pressure” that drives the charge through the circuit. The units are joules/coulomb.The units are joules/coulomb.

Electric potential – voltage – comes from analyzing the work and energy from the motion of a charge in an electric field.Electric potential – voltage – comes from analyzing the work and energy from the motion of a charge in an electric field.

The Equation

Think About It… Note the four expressions developed for force, electric field intensity, work and voltage. They were all derived from Coulomb’s law.

Potential Difference Potential difference is define and the work per unit chargePotential difference is define and the work per unit charge

A Test Charge in a Uniform Electric Field F=qE W=Fd W=qEd PE=qEd V=PE/q V=Ed

Electricity that moves… Current: The flow of electrons from one place to another.Current: The flow of electrons from one place to another. Measured in amperes (amps)Measured in amperes (amps) Kinetic energyKinetic energy

How can we control currents? With circuits.With circuits. Circuit: is a path for the flow of electrons. We use wires.Circuit: is a path for the flow of electrons. We use wires.

There are 2 types of currents: Direct Current (DC) – Where electrons flow in the same direction in a wire.Direct Current (DC) – Where electrons flow in the same direction in a wire.

There are 2 types of currents: Alternating Current (AC) – electrons flow in different directions in a wireAlternating Current (AC) – electrons flow in different directions in a wire

There are 2 types of circuits: Series Circuit: the components are lined up along one path. If the circuit is broken, all components turn off.Series Circuit: the components are lined up along one path. If the circuit is broken, all components turn off.

Series Circuit

There are 2 types of circuits: Parallel Circuit – there are several branching paths to the components. If the circuit is broken at any one branch, only the components on that branch will turn off.Parallel Circuit – there are several branching paths to the components. If the circuit is broken at any one branch, only the components on that branch will turn off.

Parallel Circuit

What is Resistance? The opposition to the flow of an electric current, producing heat.The opposition to the flow of an electric current, producing heat. The greater the resistance, the less current gets through.The greater the resistance, the less current gets through. Good conductors have low resistance.Good conductors have low resistance. Measured in ohms.Measured in ohms.

What Influences Resistance? Material of wire – aluminum and copper have low resistanceMaterial of wire – aluminum and copper have low resistance Thickness – the thicker the wire the lower the resistanceThickness – the thicker the wire the lower the resistance Length – shorter wire has lower resistanceLength – shorter wire has lower resistance Temperature – lower temperature has lower resistanceTemperature – lower temperature has lower resistance

Difference b/t Volts and Amps Example – you could say that…Example – you could say that… –Amps measure how much water comes out of a hose. –Volts measure how hard the water comes out of a hose.

Ohm’s Law Resistance = Voltage / CurrentResistance = Voltage / Current Ohms = Volts / AmpsOhms = Volts / Amps

Practice with Ohm’s Law OhmsVoltsAmps 410025 1515010 23015 9455 6488

What is an electromagnet? Electromagnet – a magnet made from a current bearing coil of wire wrapped around an iron or steel core.Electromagnet – a magnet made from a current bearing coil of wire wrapped around an iron or steel core.

What is a generator? Generator – a machine that changes mechanical energy to electrical energyGenerator – a machine that changes mechanical energy to electrical energy Usually use moving magnets to create currents in coils of wire.Usually use moving magnets to create currents in coils of wire.

What is a motor? Motor – a device that changes electrical energy to mechanical energy that can do work.Motor – a device that changes electrical energy to mechanical energy that can do work.

That’s It !!!!

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