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
++++++
------
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.
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