19-6 Circuits Containing
Capacitors in Series and Parallel
•Just as a resistor can be placed in series
and/or parallel, so can capacitors.
•Remember Q=CV
•In a parallel connection of capacitors, …
•Ceq = C1 + C2 + C3….etc and…
•Q=Q1 + Q2 + Q3….etc and…
•C1V + C2V + C3V….etc and…
•Q=CeqV
19-6 Circuits Containing Capacitors
in Series and Parallel (cont’d)
• In a series connection of capacitors,
1/Ceq = 1/C1 + 1/C2 +1/C3 ……and….
Q/Ceq = Q/C1 + Q/C2 +Q/C3 ……and….
V= V1+ V2 + V3 ……
See Page 569 diagrams
See Example 19-9 p570
19-8 Circuits Containing a Resistor
and Capacitor
•
•
•
•
RC circuits have resistors and capacitors.
See diagram p570.
V= e(1-e-t/RC)
The product of the resistance and capacitance is
called the time constant t of a circuit.
t=RC
When a circuit does not have a EMF, but is charged and
the charge is released across a resistor, use V=V0et/RC
See p571 diagram 19-18a
See Example 19-10 p 572
19-8 Heart Pacemakers
• One use of RC circuits is a pacemaker.
• A pacemaker can make a stopped heart
start again…our heart has a natural pacemaker
19-9 Electric Hazards; Leakage
Currents
• Most people can feel 1mA of current.
• Currents above 10mA cause severe contraction
of the muscles, and a person may not be able to
release the device and death from paralysis of
the respiratory system may occur.
• If 70mA or more passes through the torso or
heart region for more than a second, ventricular
fibrulation may occur and cause death.
• Dry skin has a resistance of 104 to 106W
... Wet skin has 103 W .
I=V/R
means 120 V could be lethal.
• See p 574
19-10 DC Ammeters and
Voltmeters
• An ammeter measures current and a
voltmeter measures potential difference.
• The crucial part of either is the
galvanometer….
• A galvanometer works on the principal of
the force between a magnetic field and a
current-carrying coil of wire.
• Some of the meters on your car’s dash are
connected as galvanometers.
• The full-scale sensitivity Im, is the current needed
to move the needle to the full-scale reading.
• An ammeter, represented by the symbol
-A- consists of a galvanometer –G- in parallel with
a resistor called a shunt resistor…with
resistance R, while the galvanometer has
resistance r. (See p 575)
See Example 19-12 and 19-13.
HOMEWORK
• P 582 36-43,55-57, 60 Due Wednesday
• Test Thursday