Transcript Lego Part II

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?
Negative
Terminal
That’s why
batteries
can
Current
Flow
Sit on a shelf for years and
Still have power !
Positive
Terminal
Electrons
andof
Electrons flow from the battery into aAwire,
depletion
collecttravel
in the from the negative to the positive
electrons is left
must
negative
on the positive
terminal
place.
terminal for the chemical reaction to take
terminal
Getting back to business…
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)
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
--
++ +
+
++
Circuit
Pathway
Neg.
Charge
DANGER!!
What is Capacitance?
Property of an electrical device that allows
it to store an electrical charge.
Or…..A “mighty” electrical spring
Like a Water Tower
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.
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
Pos. Side
Power
Source
Neg. side
Flow
Pos. Side
Power
Source
Neg. side
Flow
Shortage of -
GAP
Collection of -
A Little History
Franklins Great
OOOPs…….
Capacitor Symbols
Fixed Non-Polarized Capacitor
Fixed Polarized Capacitor
Variable 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 Factors
Area of the plates
Distance between plates
Materials separating
plates
Mad Dog Face Off
-
+
Gap
Wire or
conductor
Wire or
conductor
Really Mad Dog Face Off
- +
- +
- +
- +
- +
- +
Capacitor Plate
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.
Obviously, it's impractical to use
• That meanscapacitors
that a AA
battery
can produce
to store
any significant
amount
of power
unless
you do it at a
2.8 amps for
1 hour
at 1.5
volts.
high voltage.
• 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
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
Foil
Making a Capacitor
UP
Sideways
Cover Sheet
1. Cut Foil
Plain Paper
2. Sandwich Paper
3. Charge {10 + sec.}
4. Measure w/ Meter set @
{Volts m200}
5. Average the Three Readings
Stun Gun vs Death Ray