PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next...
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Transcript of PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next...
![Page 1: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/1.jpg)
PHY-2049Current & CircuitsFebruary ‘08
![Page 2: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/2.jpg)
News•Quiz Today•Examination #2 is on Wednesday of next
week (2/4/09)• It covers potential, capacitors, resistors and
any material covered through Monday on DC circuits.
•No review session on Wednesday – Exam Day!
![Page 3: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/3.jpg)
A closed circuit
Hot, H
ot H
ot
![Page 4: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/4.jpg)
Power in DC Circuit
R
EIVRIP
RIIRIIVPPower
VIt
QV
t
22
2
W
:Power
QVW
:isbattery by the done
workofamount The battery. by theresistor the
throughpushed is Q charge a t, In time
![Page 5: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/5.jpg)
Let’s add resistors …….
![Page 6: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/6.jpg)
Series Combinations
iiRseriesR
general
RRR
iRiRiRVVV
and
iRV
iRV
)(
:21
2121
22
11
R1 R2
i i
V1 V2V
SERIES Resistors
![Page 7: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/7.jpg)
The rod in the figure is made of two materials. The figure is not drawn to scale. Each conductor has a square cross section 3.00 mm on a side. The first material has a resistivity of 4.00 × 10–3 Ω · m and is 25.0 cm long, while the second material has a resistivity of 6.00 × 10–3 Ω · m and is 40.0 cm long. What is the resistance between the ends of the rod?
![Page 8: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/8.jpg)
Parallel Combination??
i iRR
general
RRR
so
R
V
R
V
R
Viii
iRV
11
111
..
21
2121
R1, I1
R2, I2
V
![Page 9: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/9.jpg)
What’s This???
In the figure, find the equivalent resistance between points (a) F and H and [2.5] (b) F and G. [3.13]
![Page 10: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/10.jpg)
• (a) Find the equivalent resistance between points a and b in Figure P28.6. (b) A potential difference of 34.0 V is applied between points a and b. Calculate the current in each resistor.
![Page 11: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/11.jpg)
Power Source in a Circuit
The ideal battery does work on charges moving them (inside) from a lower potential to one that is V higher.
![Page 12: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/12.jpg)
A REAL Power Sourceis NOT an ideal battery
V
E or Emf is an idealized device that does an amount of work E to move a unit charge from one side to another.
By the way …. this is called a circuit!
Internal Resistance
![Page 13: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/13.jpg)
A Physical (Real) Battery
Rr
Emfi
Internal Resistance
![Page 14: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/14.jpg)
Which is brighter?
![Page 15: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/15.jpg)
Which is Brighter
Which is Brighter???
![Page 16: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/16.jpg)
Back to Potential
Represents a charge in space
Change in potential as one circuitsthis complete circuit is ZERO!
![Page 17: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/17.jpg)
Consider a “circuit”.
This trip around the circuit is the same as a path through space.
THE CHANGE IN POTENTIAL FROM “a” AROUND THE CIRCUIT AND BACK TO “a” is ZERO!!
![Page 18: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/18.jpg)
To remember• In a real circuit, we can neglect the resistance
of the wires compared to the resistors.▫ We can therefore consider a wire in a circuit to be an
equipotential – the change in potential over its length is slight compared to that in a resistor
• A resistor allows current to flow from a high potential to a lower potential.
• The energy needed to do this is supplied by the battery.
VqW
![Page 19: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/19.jpg)
NEW LAWS PASSED BY THIS SESSION OF THE FLORIDUH LEGISLATURE.
•LOOP EQUATION▫The sum of the voltage drops (or rises) as
one completely travels through a circuit loop is zero.
▫Sometimes known as Kirchoff’s loop equation.
•NODE EQUATION▫The sum of the currents entering (or
leaving) a node in a circuit is ZERO
![Page 20: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/20.jpg)
TWO resistors again
jj
21
21
RR
Resistors SERIESfor General
RRR
or
iRiRiRV
i
R1 R2
V1 V2
V
![Page 21: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/21.jpg)
A single “real” resistor can be modeledas follows:
R
a b
V
position
ADD ENOUGH RESISTORS, MAKING THEM SMALLERAND YOU MODEL A CONTINUOUS VOLTAGE DROP.
![Page 22: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/22.jpg)
We start at a point in the circuit and travel around until we get back to where we started.
•If the potential rises … well it is a rise.•If it falls it is a fall OR a negative rise.•We can traverse the circuit adding each
rise or drop in potential.•The sum of all the rises around the loop is
zero. A drop is a negative rise.•The sum of all the drops around a circuit
is zero. A rise is a negative drop.•Your choice … rises or drops. But you
must remain consistent.
![Page 23: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/23.jpg)
Take a trip around this circuit.
Consider voltage DROPS:
-E +ir +iR = 0or
E=ir + iRrise
![Page 24: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/24.jpg)
Circuit Reduction
i=E/Req
![Page 25: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/25.jpg)
Reduction
Computes i
![Page 26: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/26.jpg)
Another Reduction Example
PARALLEL
1212
1
600
50
30
1
20
11
RR
![Page 27: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/27.jpg)
Battery
•A battery applies a potential difference between its terminals.
•Whatever else is connected (circuits, etc.), the potential between the points remains the same: the battery potential.
![Page 28: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/28.jpg)
Take a trip around this circuit.
Consider voltage DROPS:
-E +ir +iR = 0or
E=ir + iRrise
![Page 29: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/29.jpg)
Multiple Batteries
![Page 30: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/30.jpg)
START by assuming a DIRECTION for each Current
Let’s write the equations.
![Page 31: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/31.jpg)
In the figure, all the resistors have a resistance of 4.0 and all the (ideal) batteries have an emf of 4.0 V. What is the current through resistor R?
![Page 32: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/32.jpg)
Consider the circuit shown in the figure. Find (a) the current in the 20.0-Ω resistor and (b) the potential difference between points a and b.
![Page 33: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/33.jpg)
Using Kirchhoff’s rules, (a) find the current in each resistor in Figure P28.24. (b) Find the potential difference between points c and f. Which point is at thehigher potential?
![Page 34: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/34.jpg)
The Unthinkable ….
![Page 35: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/35.jpg)
RC Circuit• Initially, no current
through the circuit• Close switch at (a) and
current begins to flow until the capacitor is fully charged.
• If capacitor is charged and switch is switched to (b) discharge will follow.
![Page 36: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/36.jpg)
Close the Switch
I need to use E for E
Note RC = (Volts/Amp)(Coul/Volt) = Coul/(Coul/sec) = (1/sec)
![Page 37: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/37.jpg)
Really Close the Switch
I need to use E for E
R
E
RC
q
dt
dq
or
EC
q
dt
dqR
C
qiRE
dt
dqi since
0
Equation Loop
Note RC = (Volts/Amp)(Coul/Volt) = Coul/(Coul/sec) = (1/sec)
![Page 38: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/38.jpg)
This is a differential equation.
•To solve we need what is called a particular solution as well as a general solution.
•We often do this by creative “guessing” and then matching the guess to reality.
•You may or may not have studied this topic … but you WILL!
![Page 39: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/39.jpg)
RC
REaeCE
R
E
RC
q
dt
dq
CEq
R
E
RC
q
dt
dq
Keqq
at
p
atp
1
RCE
Ea
E/R0CEa
0for t
/)e-CE(1)(
)e-CE(1q and
-CEK
KCE0
solution from and 0q 0,When t
and 0dq/dt charged,fully is device When the
:solution particularat Look
Solution General
at-
at-
![Page 40: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/40.jpg)
Time Constant
RC
![Page 41: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/41.jpg)
Result q=CE(1-e-t/RC)
![Page 42: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/42.jpg)
q=CE(1-e-t/RC) and i=(CE/RC) e-t/RC
RCteR
Ei /
![Page 43: PHY-2049 Current & Circuits February ‘08. News Quiz Today Examination #2 is on Wednesday of next week (2/4/09) It covers potential, capacitors, resistors.](https://reader031.fdocuments.us/reader031/viewer/2022032707/56649e3b5503460f94b2d741/html5/thumbnails/43.jpg)
Discharging a Capacitorqinitial=CE BIG SURPRISE! (Q=CV)
i
iR+q/C=0
RCt
RCt
eRC
q
dt
dqi
eqq
solutionC
q
dt
dqR
/0
/0
0