Chapter 10 Capacitors

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```					Chapter 10
Capacitors
Terms to Study
Capacitance        Dielectric
Capacitive         Electrostatic Field
Capacitor          Impedance
Counter            Plates
electromotive   Working Voltage
force
Chapter 10 Capacitors

Capacitor Action

Capacitance – the ability of a
circuit or device to store
electric energy
Chapter 10 Capacitors

Capacitor Action

two conductors called
PLATES

separated by insulating
material called the
DIELECTRIC
Chapter 10 Capacitors

Capacitor functions

Blocks direct current

Alternating current can still flow
Chapter 10 Capacitors

Capacitor functions
Block direct current

Direct current

No current
to power
the light.
Chapter 10 Capacitors

Capacitor functions

Alternating current can still flow
Chapter 10 Capacitors

Capacitor Action with AC
Chapter 10 Capacitors

Capacitor functions
Used with resistors and coils to
filter or smooth out a varying
direct current – tuners in radios

Very important components in
oscillator circuits – timing
circuits
Chapter 10 Capacitors

Capacitor functions in AC
Allows AC to flow but it does
oppose the current
This opposition is called Capacitive
Reactance
Chapter 10 Capacitors

What determines the level of
Capacitance ?

1.      Area of the Plates – greater the area
the greater the capacitance DUH

2.      Spacing or distance between the
plates – closer the spacing
the greater the capacitance
Chapter 10 Capacitors
Capacitance

Dielectric Materials

Air              Paper
Mylar            Glass
Mica             Polystyrene
Ceramic material
Chapter 10 Capacitors
Units of Capacitance
Basic unit of Capacitance is the

Units most often given in
Picofarads (pF) 1 / 1,000,000 µF
Chapter 10 Capacitors
Unit of Capacitance
Named in honor of
English scientist 1791-1867
Chapter 10 Capacitors

Working Voltage
Largest value of direct voltage that can
safely be applied to a capacitor

Fixed Capacitors rated in terms of their
working voltage ( WVdc )
If a higher voltage is applied the dielectric
breaks down and begins to conduct
current and must be replaced
Chapter 10 Capacitors
Kinds of Capacitors
Fixed – specific value
1. Electrolytic –
*one plate is made from a
thin film of oxide on
metal foil

*the other plate is a paste
electrolyte - either
borax or carbon salt
Chapter 10 Capacitors      Cont.
Kinds of Capacitors

Fixed – specific value
Electrolytic –
Polarized
May have more than
one section
Chapter 10 Capacitors              Cont.
Kinds of Capacitors

Fixed – specific value
2. Ceramic Capacitors –
disk shaped or
tubular                           dielectrics
barium titanate
Thin plates of silver compound
Rated from 5 pF to .05 µF
WVdc exceed 10,000 V
Chapter 10 Capacitors                Cont.
Kinds of Capacitors
Fixed – specific value
3. Silver Mica Capacitors
thin sheet of Mica (dielectric)
Coating of silver compound
on each side of the mica.
Rated from 1 pF to
10,000 µF WVdc 500 V
Chapter 10 Capacitors              Cont.
Kinds of Capacitors

Variable Capacitors
Primarily used to tune
circuits
Trimmer Capacitors –
two metal plates
separated by a thin sheet
screw
Chapter 10 Capacitors   Cont.
Kinds of Capacitors
Mylar Capacitors
Chapter 10 Capacitors              Cont.
Capacitors in circuits
Parallel -     to get the capacitance
value that can’t be obtained from one
capacitor

C (total) = C1 + C2 + ….

= 0.03 + 0.02 µF
= 0.05 µF
Chapter 10 Capacitors             Cont.
Capacitors in circuits
Series - the applied voltage is divided
among them – similar to resistors in series
Chapter 10 Capacitors        Cont.
Charging Capacitors
Unlike a battery it does not
create it’s own electricity

Once charged it can be used
as a voltage source

Charge can be stored then
Chapter 10 Capacitors          Cont.
Charging Discharging Capacitors
Charging

Discharging
Chapter 10 Capacitors
Capacitors Safety
Electrolytic Capacitors used in
High Voltage rectifier circuits should
be discharge before handled

These are found in Televisions - hold their
charge for many hours after being
turned off

Using a 10,000K Ω resistor can be
connected in series to reduce
sparking at the terminals
Chapter 10 Capacitors
Capacitors Defects

Fixed Capacitors – become shorted
because of direct contact of the plates

Variable Capacitor – defective because
of shorted plates

Replace defective capacitors with one
having the same capacitance or
tolerance and type of dielectric and
temperature characteristics
Chapter 10 Capacitors
Capacitors Testing
Short Circuits – tested with an
Ohm Meter – will show continuity
with low resistance

Leaky or shorted capacitors
should be replaced
Chapter 10 Capacitors

Building a Capacitor
Building a Capacitor

1. Cut two pieces of aluminum
foil 4 inches wide x 12 inches
long

2. Cut four pieces of plastic
wrap 12 inches wide x 12
inches long
Building a Capacitor
Building a Capacitor

3. Using multi strand wire, cut
two pieces 6” long and strip
both ends and fan the strands
on one end
Building a Capacitor

4.Attach one wire to one of the
aluminum plates and the other to the
other aluminum plate. Attach to
different ends using clear scotch tape
Building a Capacitor

4. Fold the foil over covering the
connection.
Building a Capacitor

4. Fold the foil over, covering the
connection.

5. Do the same for the second piece of
foil, but at the opposite end..

6. Place the first piece of plastic wrap
flat on the table.
7. Place the first piece of foil on the
plastic wrap .
Moment of Silence

Capacitor Construction
Darley - 1475
Pottinger – 2914
Deiters - 3342
Kriegel – 3557
Burns – 2175
Yang – 1856
Benefield – 1814
Stephens – 1828
Dieumgarde - 1984
Splitler – 1870
Zanow - 1748
Chapter 10 Capacitors

Review Main Ideas
p. 138
1-23

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