What is a conductor? What is an insulator?

Agenda for Tuesday Feb 22nd 1.Electricity notes/demo

All late work is due by Next Friday, March 4th

Atoms…

• Have neutronsneutrons, protonsprotons, and electronselectrons.• Protons are positivelypositively charged• Electrons are negativelynegatively charged

Electrons…

• Are located on the outerouter edges of atoms…they can be movedmoved.• A concentrationconcentration of electrons in an

atom creates a net negativenegative charge.• If electrons are strippedstripped away, the

atom becomes positivelypositively charged.

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The world is filled with electrical charges:

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What is this electrical potential called?

• Static ElectricityStatic Electricity

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Static Electricity

• The build upbuild up of an electric charge on the surfacesurface of an object.• The charge builds up but does not does not

flow.flow.• Static electricity is potential energypotential energy.

It does notnot move. It is storedstored.

Static Discharge…

• Occurs when there is a lossloss of static electricity due to three possible things:• FrictionFriction - rubbing• ConductionConduction – direct contact• InductionInduction – through an electrical

field (not direct contact)

Electricity that moves…

• Current (Current (II)): The flow of electrons from one place to another.• Measured in amperesamperes (amps)• KineticKinetic energy

How can we control currents?

• With circuitscircuits.• CircuitCircuit: is a pathpath for the flow of

electrons. We use wireswires.

There are 2 types of currents:

• Direct Current (DC)Direct Current (DC) – Where electrons flow in the samesame direction in a wire.

There are 2 types of currents:

• Alternating Current (AC)Alternating Current (AC) – electrons flow in differentdifferent directions in a wire

There are 2 types of circuits:

• Series CircuitSeries Circuit: the components are lined up along oneone path.

• If the circuit is broken, allall ccomponents turn off

Series Circuit

There are 2 types of circuits:

• Parallel CircuitParallel Circuit – there are severalseveral branching paths to the components

• Connected side by side

• If the circuit is broken at any one branch, only the components on that branch will only the components on that branch will turn offturn off

Parallel Circuit

Conductors vs. Insulators

• ConductorsConductors – material through which electric current flows easilyeasily.

• InsulatorsInsulators – materials through which electric current cannot movecannot move.

Examples

• ConductorsConductors:–Metal–Water

• InsulatorsInsulators:–Styrofoam–Rubber–Plastic–Paper

What is current?

Agenda for Wednesday Feb 23rd 1.Ohm’s law

All late work is due by Next Friday, March 4th

Electricity that moves…

• Current (Current (II)): The flow of electrons from one place to another.• Measured in amperesamperes (amps)

What is Resistance?

• The oppositionopposition to the flow of an electric current –Can produce heatheat• More More resistance, lessless current gets

through• GoodGood conductors have lowlow resistance• Measured in ohmsohms

What Influences Resistance?

• Material of wireMaterial of wire – aluminum and copper have low resistance

• ThicknessThickness – the thicker the wire the lower the resistance

• LengthLength – shorter wire has lower resistance

• TemperatureTemperature – lower temperature has lower resistance

Potential Difference

• Work that must be done against electric forces to move a unit charge from one point to another– Charges move from negative to

positive

– Measured in volts (V)

– Car battery there is a voltage of 12 V across the negative and positive

More on Voltage?

• Voltage is the measure of energymeasure of energy given to the charge flowing in a circuit

• The greatergreater the voltage, the greatergreater the force or “pressure”the force or “pressure” that drives the charge through the circuit

Difference between Volts and Amps

• Example – you could say that…–AmpsAmps measure how muchhow much water

comes out of a hose.–VoltsVolts measure how hardhow hard the water

comes out of a hose.

Ohm’s Law

• Resistance = Voltage / Current

• Ohms = Volts / Amps

Practice with Ohm’s Law

OhmsOhms VoltsVolts AmpsAmps

44 100100 2525

1515 150150 1010

22 3030 1515

99 4545 55

66 4848 88

What is an electromagnet?

• ElectromagnetElectromagnet – a magnet made from a current bearing coilcurrent bearing coil of wire wrapped around an iron or steel iron or steel core.core.

What is a generator?

• GeneratorGenerator – a machine that changes mechanicalmechanical energy to electricalelectrical energy• Usually use movingmoving magnets to

create currentscurrents in coils of wire.

What is a motor?

• MotorMotor – a device that changes electricalelectrical energy to mechanicalmechanical energy that can do workwork.