Standards/Plan
Standards
Standards
Standards
Standards
WARM UP
NO WARM UP TODAY!
10 minutes to
finish your
Lifemap!
Simple
Harmonic
1) An electron
isMotion
fired up(SHM)
between two charged plates,
as shown. Which of the
following identifies the field
and motion of the electron
as it passes through the
field?
Simple
Harmonic
Motion
(SHM)
2) An insulating
plate
is rubbed
with a cloth to give it a
charge. A conducting plate, attached to an insulating
handle, is then placed on top of the insulator and briefly
grounded by touching it. The conductor is held by the
insulating handle and lifted from the insulator plate.
Which of the following is true?
Simple Harmonic Motion (SHM)
Warm Up
3) If the voltage across a circuit is kept constant
and the resistance is halved, by what factor does
the circuit’s current change?
a) 1/2
c) 1/4
b) 2
d) 4
4) If the current supplied to a resistor is tripled,, by
what factor does the circuit’s power change?
a) 1/3
c) 1/9
b) 3
d) 9
Warm Up
5) A computer monitor runs on 120 Volts,
and has a resistance of 100 ohms. The
amount of power it dissipates is closest to:
Warm Up
5)
Warm Up
6) What is the equivalent resistance of the
circuit?
Warm
Up
7) A battery
(of voltage V or 2V) and resistors
(of R or 2R) are connected in various
combinations as shown below. In which
circuit is the most power dissipated?
Warm Up
Lesson
Electricity and Circuits
The movement of
electrons is called
ELECTRICITY!!!
Current
I Avg
Q

t
V  IR
P  IV
I - current in amperes
Q - charge in Coulombs
t
- time in seconds.
V - Voltage in volts
I - Current in amps
t - Resistance in ohm
Ohm ' s Law
P - Power in Watts
Series Circuits with multiple resistors
• A circuit in which there is only one current
path
Series Circuit
• Current is the same in all resistors
I = I1 = I2 = I3 = I4
• Voltage is distributed among the resistors
depending on resistance.
V = V1 + V2 + V3
• Total Resistance is the sum of all resistors.
RT= R1 + R2 + R3
Parallel Circuits
 A circuit in which there are several
current paths
Parallel Circuit- Rules CHANGE!!
• Current is the added in all resistors
IT = I1 + I2 + I3
• Voltage is equal among the resistors
VT = V1 = V2 = V3
• Total Resistance is the reciprocal of all resistors
1/RT = 1/R1 + 1/R2 + 1/R3
Kirchhoff’s Rule - NEW
• Junction Rule – total CURRENT INto a
junction must equal the total CURRENT
OUT of the junction:
Sample problem
• Find the current I4 (magnitude and direction).
3.0 A
I4
4.0 A
1.5 A
You Try!
• 1) Current in WX:
2) Current in XZ
3) Current in ZB
Combination Circuits
•Some circuits have both SERIES and
PARALLEL parts to them. These are called
COMBINATION circuits. They are difficult
•Step 1: Simplify the circuit to find Total R
•Step 2: Get the TOTAL CURRENT
•Step 3: IT = Iseries
•Step 4: Solve each piece separately
Announcements
1. Turn in progress reports
2. Circuits_ Assignment 2
3. Circuits QUIZ on Friday!
Circuits FR_2: Student led response
IF given 120V, the bulbs
would be 60W. But based on
the set up of the circuit they
are not going to get 120V
Miscellaneous Info WHITEBOARDS
You know that
drawer in the
kitchen where you
put all the random
stuff that doesn’t
exactly go
anywhere else?
Miscellaneous Info
1. Internal
Resistance
2. Resistivity
3. Ohmic
Resistors
• 9V batteries actually produce
MORE THAN 9V
• This is because in the real world
batteries have a small amount of
INTERNAL RESISTANCE.
Electro Motive Force vs. Voltage
Emf = V for a battery with no
“internal resistance”
EMF = 
ΔV = Terminal Voltage
The voltage the
battery actually
produces
The voltage the
battery provides to the
circuit
V    Ir
Example
V    Ir
• The internal resistance of a 1.5 V cell is 4 .
What is its terminal voltage (actual voltage)
when it is supplying 2 mA of current?
Example
V    Ir
• A battery has an emf of 12.0 V and delivers
150.0 mA when connected to a 75.0  load.
What is the internal resistance of the
battery?
1) In the circuit, the
emf, ,produced by the
battery is 24V, and the
load resistance of R is
10 Ω. If the ammeter
reads 2.0A in the circuit,
what is the terminal
voltage of the battery?
2) What is the
internal resistance of
the battery?
Miscellaneous Info
1. Internal
Resistance
2. Resistivity
3. Ohmic
Resistors
So what actually determines the
resistance of an a resistor?
So what actually determines the
resistance of an a resistor?
1. L:
LENGTH
length of resistor (m)
2. A:
CROSS
crossSECTIONAL
sectional area
AREA
of resistor (m2)
MATERIAL
3. :
resistivity ( m)
R
L
A
• Resistivity, ρ –is a property of the material.
• low ρ  conductors
high ρ  insulators
Sample problem
• What is the resistivity of a substance which has a
resistance of 1000  if the length of the material
is 4.0 cm and its cross sectional area is 0.20 m2?
R
L
A
Sample problem 2
• What is the resistance of a mile (1600m) of
copper wire if the diameter is 5.0 mm?
R
L
A
Conceptual 1
• A certain wire has resistance R. The resistance of
another wire, identical with the first except for
having twice its diameter, is
R
L
A
Conceptual 2
• Wire 1 has a length L and a circular cross section
of diameter D. Wire 2 is constructed from the
same material as wire 1 and has the same shape,
but its length is 2L, and its diameter is 2D. Is the
resistance of wire 2:
• (a) the same as that of wire 1
• (b) twice that of wire 1
• (c) half that of wire 1
R
L
A
Conceptual 3
• The five resistors shown below have the lengths
and cross-sectional areas indicated and are made
of material with the same resistivity. Which
resistor has the least resistance?
Individual Practice
• A metal wire 10 m long has a cross-sectional area
of 1  10-3 m2. The resistivity of the metal is 1.2
 10-8  m.
1.What is the resistance of the wire?
2.What is the resistivity if the diameter of the wire
is doubled?
3.What is the resistance if the diameter of the
wire is doubled?
4.What is the resistance if the length of the wire is
doubled?
Miscellaneous Info
1. Internal
Resistance
2. Resistivity
3. Ohmic
Resistors
1. Ohmic Resistors
2. Graphs w/ Circuits
•
The super simple version
Ohmic
Non Ohmic
Obey Ohm’s Law
V = IR
Does not obey the
law
One more Free Response
(short one) to practice
Capacitors and RC Circuits
• This stuff is less likely to show up on a
test, but it is something good to know.
• Just remember the basics and you will
be fine!
Capacitor
• Stores electric charge and energy.
• A capacitor is two conducting plates
separated by a distance:
The capacitance relates the charge
to the potential difference:
Charge on the
capacitor
Sample Problem: A 0.75 F capacitor is
charged to a voltage of 16 volts. What is the
magnitude of the charge on the capacitor?
Capacitors
• When a capacitor is connected to a
battery, charges immediately start
flowing onto the plates of the capacitor.
• As the charge on the capacitor's plates
increases, this current decreases
• Finally, the current stops because the
capacitor is fully charged. This is called
the STEADY STATE
Charge vs. Time for RC circuit
Current vs. Time for an RC Circuit
Capacitors
• When a capacitor is in a STEADY STATE
it basically just holds a charge and sits
there.
Capacitors
1. What is the voltage of the capacitor?
2. How much charge does it hold?
Capacitors
1. What is the voltage of the capacitor?
2. How much charge does it hold?
100
24V
300 
40 x10-6 F
How to treat capacitors in a circuit
Resistors
Use Energy
Capacitors
Store energy
•“Rules” for equivalent
capacitance are REVERSED
from the “Rules” for equivalent
resistance.
Capacitors in Series
• Equivalent capacitance (SERIES)
1
1
1
1
 


Ceq
C1 C2
i Ci
1.What is the equivalent resistance of a 1uF
and an 8 uF capacitor wired in series?
Capacitors in Parallel
• Equivalent Capacitance (PARALLEL)
Ceq   Ci  C1  C 2  
i
1.What is the equivalent resistance of a 1uF
and an 8uF capacitor wired in parallel?
Review Sheet
1. Complete this sheet as part of your
studying for the quiz tomorrow
2. Quiz:
50%MC
50% FR
The review sheet has practice for both.
The free response will test the EXACT
SAME CONCEPT. A complex circuit,
and a circuit w/ a capacitor.
R
I
V
P
R1
R2
R3
TAL
R
R1
R2
I
V
What determine Capacitance:
o A
C
d
Increase
Plate Area
=
Increase
Capacitance
Increase
Distance
=
Decreased
Capacitance