Atoms…Atoms…

Have Have neutronsneutrons, , protonsprotons, and , and electronselectrons..

Protons are Protons are positivelypositively charged chargedElectrons are Electrons are negativelynegatively charged charged

Electrons…Electrons…

Are located on the Are located on the outerouter edges of edges of atoms…they can be atoms…they can be movedmoved..

A A concentrationconcentration of electrons in an of electrons in an atom creates a net atom creates a net negativenegative charge.charge.

If electrons are If electrons are strippedstripped away, the away, the atom becomes atom becomes positivelypositively charged. charged.

+-

++

++

The world is filled with The world is filled with electrical electrical chargescharges::

+

+

+

+

+

-

-- -

--

- --

What is this electrical What is this electrical potentialpotential called?called?

Static ElectricityStatic Electricity

- --

--

-

- ++++

+

Static ElectricityStatic Electricity The The build upbuild up of an electric charge on the of an electric charge on the surfacesurface of an object. of an object. The charge builds up but The charge builds up but does not flow.does not flow. Static electricity is Static electricity is potential energypotential energy. It does . It does notnot move. It is move. It is storedstored..

Static Discharge…Static Discharge…

Occurs when there is a Occurs when there is a lossloss of of static electricity due to three static electricity due to three possible things:possible things:

FrictionFriction - rubbing - rubbingConductionConduction – direct contact – direct contactInductionInduction – through an electrical – through an electrical field (not direct contact)field (not direct contact)

Electricity that Electricity that movesmoves……

CurrentCurrent: The flow of electrons : The flow of electrons from one place to another.from one place to another.

Measured in Measured in amperesamperes (amps) (amps)KineticKinetic energy energy

How can we How can we controlcontrol currents? currents?

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

electrons. We use electrons. We use wireswires..

There are 2 types of currents:There are 2 types of currents:

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

There are 2 types of currents:There are 2 types of currents:

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

simple circuitssimple circuits

Here is a simple electric circuit. It has a cell, a

lamp and a switch.

To make the circuit, these components are

connected together with metal connecting wires.

cell

lamp

switch

wires

simple circuitssimple circuitsWhen the switch is closed, the lamp lights up. This is because there is a continuous path of metal for the electric current to flow around.

If there were any breaks in the circuit, the current could not flow.

circuit diagramcircuit diagram

battery

switch

lamp

wires

Scientists usually draw electric circuits using symbols;

circuit diagramscircuit diagramsIn circuit diagrams components are represented by the following symbols;

battery

switch

motorammeter

voltmeter

resistor

types of circuittypes of circuit

There are two types of electrical circuits;

SERIES CIRCUITS PARALLEL CIRCUITS

The components are connected end-to-end, one after the other.

They make a simple loop for the current to flow round.

SERIES CIRCUITS

If one bulb ‘blows’ it breaks the whole circuit and all the bulbs go out.

PARALLEL CIRCUITS

The current has a choice of routes.

The components are connected side by side.

If one bulb ‘blows’ there is still be a complete circuit to the other bulb so it stays alight.

measuring current

Electric current is measured in amps (A)

using an ammeter connected in series in

the circuit.

A

measuring currentThis is how we draw an ammeter in a circuit.

SERIES CIRCUIT PARALLEL CIRCUIT

A A

measuring currentSERIES CIRCUIT

PARALLEL CIRCUIT

• current is the same

at all points in the

circuit.

2A 2A

2A

• current is shared between the components

2A2A

1A

1A

Conductors vs. InsulatorsConductors vs. Insulators

ConductorsConductors – material through – material through which electric current flows which electric current flows easilyeasily..

InsulatorsInsulators – materials through – materials through which electric current which electric current cannot cannot movemove..

ExamplesExamples

ConductorsConductors::MetalMetalWaterWater

InsulatorsInsulators::StyrofoamStyrofoamRubberRubberPlasticPlasticPaperPaper

What is Resistance?What is Resistance?

The The oppositionopposition to the flow of an to the flow of an electric current, producing electric current, producing heatheat..

The The greatergreater the resistance, the the resistance, the lessless current gets through. current gets through.

GoodGood conductors have conductors have lowlow resistance.resistance.

Measured in Measured in ohms.ohms.

What Influences Resistance?What Influences Resistance?

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

ThicknessThickness – the thicker the wire the – the thicker the wire the lower the resistancelower the resistance

LengthLength – shorter wire has lower – shorter wire has lower resistanceresistance

TemperatureTemperature – lower temperature has – lower temperature has lower resistancelower resistance

What is Voltage?What is Voltage?

The The measure of energymeasure of energy given to given to the charge flowing in a circuit.the charge flowing in a circuit.

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

Difference between Volts and Difference between Volts and AmpsAmps

Example – you Example – you could say that…could say that…AmpsAmps measure measure

how muchhow much water water comes out of a comes out of a hose.hose.

VoltsVolts measure measure how how hardhard the water the water comes out of a comes out of a hose.hose.

Ohm’s LawOhm’s Law Ohm's Law defines the relationships between (P) power,

(E) voltage, (I) current, and (R) resistance.

Resistance = Voltage / CurrentResistance = Voltage / Current

Ohms = Volts / AmpsOhms = Volts / Amps

Practice with Ohm’s LawPractice with Ohm’s Law

OhmsOhms VoltsVolts AmpsAmps

44 100100 2525

1515 150150 1010

22 3030 1515

99 4545 55

66 4848 88