17.4. Resistors in Series and Parallel http://www.ck12.org
resistance. This may present a danger to the electronic element with the small resistance from joule heating.
d. What joule heating does the 24Ωresistor experience?
P=IV=
(
10
27
A
)(
80
9
V
)
=
800
243
W= 3. 29 W orP=I^2 R=
(
10
27
A
) 2
( 24 Ω) =
2400
729
→
800
243
W= 3. 29 W
Summarizing Two Important Results for Analyzing Circuits
Kirchhoff’sLaws
- The sum of the currents entering any junction must equal the sum of the currents leaving any junction.
- The sum of the potential changes around any closed circuit loop must equal zero.
The first is a statement of charge conservation and the second is a statement of the conservation of energy.
http://www.youtube.com/watch?v=ByvywQ92fdw
CapacitorsinElectricalCircuits
In an earlier discussion, we mentioned that capacitors can store and release energy. A camera flash was given as an
example of a discharge of energy by a capacitor.
Figure17.14 shows a capacitorCin a circuit charged by a battery.
The capacitor becomes fully charged (not instantly, of course) after the switchS1 is closed. The time for the capacitor
to fully charge depends upon the capacitance of the capacitor and the resistorRin the circuit. When the capacitor is
fully charged, the current will cease, and the potential difference between the plates of the capacitor will equal the
voltage of the battery,V.
FIGURE 17.14
If the switchS1 is now open, disconnecting the battery from the capacitor, and the switchS2 is closed, the capacitor
will discharge through the lampL. The lamp will initially glow very bright and then begin to dim as the current from
the capacitor diminishes. This is the way a camera flash operates.