Capacitors. First… How Does a Battery Work? A chemical reaction formed in a “CELL”. Slow but constant discharge. Kind of like an old person or turtle.

Capacitors

First… How Does a Battery Work?

• A chemical reaction formed in a “CELL”. Slow but constant discharge.

• Kind of like an old person or turtle.

A battery is essentially a can full of chemicals that produce electrons –

electrochemical reaction.

So HOW does it work?

Positive Terminal

Negative Terminal

Electrons collect in the negative terminal

A depletion of electrons is left on the positive terminal

Current Flow

Electrons flow from the battery into a wire, and must travel from the negative to the positive terminal for the chemical reaction to take place.

That’s why batteries canSit on a shelf for years and

Still have power !

What do we use capacitors for?!

Store whopping amounts of electrostatic energy

Used to oppose changes in circuit VOLTAGE

Deliver SMOOTH voltage throughout circuit, or holds up a voltage level (Prevents Voltage DIP)

Getting back to business…

What do Capacitors look like?

A family of capacitors…

Do Not EVER, EVER, EVER, EVER, EVER FORGET THIS!

• Never ever take your television set apart. EVER

• Capacitors are a special LEGOS as they are the only electrical device we use that stores electrical energy

• Like a Jack Rabbit or spring released all at once

++

++

+

+

------

-

Neg. Charge

Circuit Pathway

DANGER!!

What is Capacitance?

Property of an electrical device that allows it to store an electrical charge.

Or…..A “mighty” electrical spring

One way to visualize the action of a capacitor is to imagine it as a water tower hooked to a pipe. A water tower "stores" water pressure -- when the water system pumps produce more water than a town needs, the excess is stored in the water tower. Then, at times of high demand, the excess water flows out of the tower to keep the pressure up. A capacitor stores electrons in the same

way, and can then release them later.

Like a Water Tower

The difference between a capacitor and a battery is that a capacitor can dump its entire charge in a tiny fraction of a second, where a battery would take minutes to completely discharge.

Electrons on the Move

The Electron Hole

• A positive ion attracts negative electrons. (that’s why electricity flows – to +)

• When an electron moves from its valance ring it leaves a “HOLE”

• A negative electron tries to fill the void while another electron fills another “hole”

• In a sense the “hole” moves

Let’s Make a HOLE!!!

This demonstration will…..

Explain why……..

1.Electricity can travel so fast

2.How an electron hole forms

3.Capacitance and Potential Difference

Flow

Power Source

Neg. sidePos. Side

Power Source

Neg. sidePos. Side

Flow

GAPShortage of -

Collection of -

A Little History

Franklins Great OOOPs…….

Capacitor Symbols

Fixed Polarized Capacitor

Variable Capacitor

Fixed Non-Polarized Capacitor

Capacitor Design

• Electrostatic Fields on the end of two plates separated by a dielectric material

• Fixed and Variable design

Plates of Electrons

Types of Dielectric Materials

• Air or Vacuum

• Rubber

• Oil

• Paper

• Mica

• Glass

• Ceramic

Discharge FactorsArea of the plates

Distance between plates

Materials separating plates

Wire or conductor

Wire or conductor

- +Gap

Mad Dog Face Off

++++++

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Capacitor Plate

Really Mad Dog Face Off

Charging & Discharging a Capacitor

Lightning as a HUGE Capacitor? Two Huge plates separated by a dielectric…..

How Big is BIG?• The coulomb is the international standard unit of electric charge,

named after Charles-Augustin de Coulomb

• 1 coulomb is the amount of electric charge transported by a current of 1 ampere in 1 second…

• The amount of electrical charge in 6.241506×1018 electrons 6,241,506,000,000,000,000

• Capacitance is measured in Farads

• Farad = amount of capacitance for which a potential difference of 1 volt results in a static charge of 1 coulomb

• Or… the amount of capacitance that requires one second for a one ampere flow of charge to change the voltage by one volt.

1 Farad = The amount of capacitance that requires one second for a one ampere flow of charge to change the voltage by one volt

• A standard alkaline AA battery holds about 2.8 amp-hours.

• That means that a AA battery can produce 2.8 amps for 1 hour at 1.5 volts.

• There are 3,600 seconds in one hour.• To store one AA battery's energy in a

capacitor, you would need 3,600s * 2.8A /1.5v = 6,720 farads!!

Howstuffworks.com

Obviously, it's impractical to use capacitors to store any significant

amount of power unless you do it at a high voltage.

MacGyver at work

MacGyvers First Name

A little known fact is that MacGyver's first name is "Angus" (Scottish heritage).Real Name: Richard Dean Anderson

Making a Capacitor

Plain Paper

Foil

UP

Sideways Cover Sheet

1. Cut Foil

2. Sandwich Paper

3. Charge {10 + sec.}

4. Measure w/ Meter set @ {Volts m200}

5. Average the Three Readings

Stun Gun vs Death Ray