“What is Electricity?” Review

Atomic Structure

• What is an Element?

Elements

The simplest form of matter

• What is an Atom?

Atoms

The smallest piece of an element that contains all properties of that element

• What 3 particles make up atoms?

Components of an Atom

Electrons

Negatively charged atomic particles

Protons

Positively charged atomic particles

Neutrons

Uncharged atomic particles

• What determines the atomic number of an atom?

• What is the atomic number of Copper (Cu)?

Atomic Number

The atomic number is equal to the number of protons in the nucleus of an atom.

The atomic number identifies the element.

How many protons are in this nucleus?

Periodic Table of Elements

Which element has 4 protons?NASA

Electrons

For this unit, we mainly care about electrons in atoms.

Why?

It is important to understand the “how and why” of the movement of electrons to understand electricity.

• Draw a representation of a Sulfur atom (Atomic Number 16).

• Draw a representation of a Helium atom (Atomic Number 2)

Filling order:

1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, …

Electron Orbits

Atoms like to have their valence level either filled (8) or empty(0) of electrons.

How many electrons are in the valence level?

6

Sulfur has space to gain two electrons in its valence level.

• What is a valence electron?

• How many valence electrons do conductors have?

• How many valence electrons do insulators have?

• How about semiconductors?

Conductors and Insulators

Conductors Insulators

Electrons flow easily between atoms

1-3 valence electrons in outer orbit

Low Electronegativity

Good Conductors: Silver, Copper, Gold, Aluminum . . .

Electron flow is difficult between atoms

5-8 valence electrons in outer orbit

High Electronegativity

Examples: Mica, Glass, Rubber, Plastic . . .

What is a Multimeter?

An instrument for measuring the properties of an electrical circuit

Manual vs. Auto Ranging Where should you set the meter if you expect a reading around . . .

1000 volts200 volts

20 volts

2000 millivolts

200 millivolts

6 volts

50 millivolts

800 millivolts

800 volts

125 volts

History

Ben Franklin suggested that . . .

. . .opposite charges attract

and like charges repel.

+ -

History

Ben Franklin suggested that . . .

. . .opposite charges attract

and like charges repel.

+ +

The Law of Charges explains why the electrons continue to be bonded to the nucleus.

Electron Flow

An electron from one atom can knock out an electron from another atom.

Electron Flow

Electricity is created as electrons collide and transfer from atom to atom.

Play Animation

What Makes Up Electricity?

Let’s compare it to something we know --- Water!

Water Analogy

Tank = Battery

Pipe = Wiring

Faucet = Switch

Tank Faucet

Pipe

• What is current?

Current

Current: The flow of electric charge

When the faucet (switch) is off, is there any flow (current)?

NO

When the faucet (switch) is on, is there any flow (current)?

YES

Tank (Battery) Faucet (Switch)

Pipe (Wiring)

Current in a Circuit

When the switch is off, there is no current.

When the switch is on, there is current.

off onoff on

• What is voltage?

Voltage

Voltage: The force (pressure) behind the flow of current

When the faucet (switch) is off, is there any pressure (voltage)?

YES – Pressure (voltage) is pushing against the pipe, tank, and the faucet.

When the faucet (switch) is on, is there any pressure (voltage)?

YES – Pressure (voltage) pushes flow (current) through the system.

Tank (Battery) Faucet (Switch)

Pipe (Wiring)

Voltage in a Circuit

The battery provides voltage that will push current through the bulb when the switch is on.

off onoff on

• What is resistance?

Resistance

Resistance: The opposition to the flow of current.

What happens to the flow (current) if a rock gets lodged in the pipe?

Flow (current) decreases.

Tank (Battery) Faucet (Switch)

Pipe (Wiring)

Resistance in a Circuit

Resistors are components that limit the flow of electricity.

Reducing current causes the bulb to become more dim.

off on

Resistor

What types of electricity are there?

Types of Electricity

Static ElectricityThe electrical charge an object develops as a result of having an unequal number of protons and electrons.

Current ElectricityThe movement of electrons through a conductor.

Static Electricity

• Uncontrollable Electricity

• Lightening

• Static Cling

• Wool socks on a carpet “shocks”

• What are the two types of current electricity?

• What is the difference between these two?

Current Electricity

Two Types:

Alternating Current (AC)

Direct Current (DC)

Direct Current

The electrons flow in the same direction all the time, from negative to positive.

- +

Direct Current

Comes from• Batteries• Converted from Alternating Current

Used for electronic devices including• Computers• iPods• Cell phones• Anything that has a “charger”

Alternating Current

The electrical current (movement of electrons) changes direction.

Alternating Current

Comes from Generators• Coal burning and nuclear power plants• Hydroelectric power plants• Wind and solar generators

Used for• Motors• Heaters• Lights• Anything that plugs into the wall

What is a Magnet?

An object that is surrounded by a magnetic field and has the property of attracting iron or steel

Where are Magnets?

Magnets. . . Generate electricity

Image courtesy of DOE/NREL

Image courtesy of DOE/NREL

Are in motors

Where are Magnets?

Magnets. . .

Power car windows & locks

Image courtesy of NASA

Are used in Magnetic Resonance Imaging (MRI)

• If a large magnet breaks into the small pieces what will their poles be?

SN

North and South Poles of a Magnet

Magnets have a north and south pole.• If a magnet is broken into smaller pieces, each piece will still have a north and south pole.

•Opposite poles attract, like poles repel.

N S N S

N S NS

N

S

N

S

N

S

N

S

• How do compasses work?

The Earth as a Magnet

The Earth is a large magnet.

North Pole

South Pole

Compasses work as a result of the Earth’s magnetic field.

• What is an electromagnet?

Electromagnets

Magnets are created by passing a current through a wire.

Electromagnets are generally wire wrapped around an iron core.

Electromagnets are turned on and off when the current is switched on and off.

• How can you switch the poles of an electromagnet?

Electromagnets

N

S

Electromagnet ends change between north and south depending on the direction of the current.

S

N

• What parts make up a motor?

Parts of a Basic DC Motor

N SN S

DC Source

ArmatureCommutator

Brush

Commutator

Brush

Motor: A device used to convert electric energy into mechanical energy.

PermanentMagnet

PermanentMagnet

Parts of a Small DC Motor

Armature

Commutator

PermanentMagnets

Brushes

WireConnections

• What is an electric generator?

Electric Generators

N SN S

Mechanical motion turns the armature which creates current.

Many DC motors can function as a generator.

Generator: A device used to convert mechanical energy into electrical energy.

• Explain the steps by which electricity goes from the power plant to your home.

From the Power Plant to Your Home

Power plants generate electricity.

Image courtesy of Sacramento Municipal Utility District

From the Power Plant to Your Home

Step up transformers increase voltage for transmission across large towers.

Increased voltage increases efficiency.

From the Power Plant to Your Home

Large towers transmit electricity over long distances.

Images courtesy of DOE / NREL

From the Power Plant to Your Home

Step down transformers reduce voltage at substations to acceptable levels for the end user.

From the Power Plant to Your Home

Electricity arrives at your home at a junction box.

Usage is measured with a meter.

• Briefly explain how Maglev Trains work