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Unit Packet Contents
1. Notes 1: Flowing Charges
2. Concept Development: Electric Current
3. Guided Practice: Current & Resistance
4. Notes 2: Ohm’s Law and Power
5. Concept Development: Ohm’s Law & Power
6. Guided Practice: Ohm’s Law and Power
7. Notes 3: Series and Parallel Circuits
8. Guided Practice: Series and Parallel Circuits
9. Notes 4: Combination Circuits
10.Guided Practice: Combination Circuits
11.Independent Practice: Combination Circuits
Textbook Assignments:
1. Due Monday 4/7
Read pages 531 – 544
Do page 545
Review Questions 1-17, 23-25
Plug and Chug
26-29
2. Due Friday 4/25
Read pages 548 – 558
Do page 559
Review Questions 1-15
Think and Explain 20-22
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Name__________________________
Regents Physics
Date_____________________
Notes: Flowing charges
Objectives:
1. Define electric current and state its SI unit.
2. Solve problems involving current, charge and time.
3. Distinguish between conventional current and electron flow.
4. Solve problems that relate current, potenital difference and resistance.
Flow of Electric Charge
pressure to a reservoir of
 Water will spontaneously flow from a reservoir of higher
______________________
____________________
lower pressure
 Similarly electric charges will spontaneously flow from a place of ________________
potential to a place of
higher
________________
lower potential they can do work.
Consider two oppositely charged plates:
+
+
+
+
+
+
Place of _______
lower
potential for electrons
-
Place of __________
higher
potential for electrons
-
-
-
 An electron has higher potential energy at the negatively charged plate and can ____________________ as it
falls
the place of higher potential to the place of lower potential.
dofrom
work
 Providing a ______________________
coducting wire for the charge to flow through makes it possible to harness the work
the charge can do.
 Electric current is the quantity of ____________________through
a cross section of a conductor
electric charge
per__________________.
unit time
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 In the language of mathematics:
I = current (amperes = coulomb/second)
Q = charge (coulomb)
t = time (seconds)
q
I
t
Example problem: If a conductor has a current of 1 ampere flowing through it, how many electrons are flowing
per second?
Example problem What is the electric current in a conductor if 240 coulombs of charge pass through it in 1.0
minute?
Current and Potential Difference
electrons
 Very often when charge is flowing it is the result of flow of __________________
charged ions
 Charge may also flow as a result of _________________________
flowing
 Consider a positive and negative charge with a potential difference
positive charges in elecric circuits.
 By convention current is considered to flow in the direction of ______________________
(Opposite direction of __________________)
electrons
positive
Flow of ____________
charges
+
Direction of electron flow
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Sources of electrical energy
charged poles
 Batteries -- Chemical reactions cause _______________________
with a potential difference.
positive pole to ______________________.
 Electrons spontaneously flow from ___________________
negative pole
 Generators -- Mechanical energy in a magnetic
______________________
is converted to an electrical potential
field
difference.
Resistance to Charge Flow
 Water being pumped through a hose may experience resistance due to ________________
if it were forced
friction
to travel through a zig-zag hose.
 Flowing electric charges usually do work because of _______________________
that they experience when
resistance
trying to flow.
tungston wire have lots of collisions with atoms, make
 Ex: Electrons flowing through a ________________________
them hot until they glow. (incandescent light)
 Resistance for a given piece of wire depends on the:
greater
length
o ________________
of the wire; A longer wire has _________________
resistance.
o ________________
of the wire: a fatter wire has ___________
diameter
greater resistance.
o __________________
temperature of the wire; a hotter wire has ____________
greater resistance.
o the __________________
properties
of the material that the wire is made of; e.g. gold is a better conductor
than ____________________
aluminum
 The resistance of a given piece of wire at a given temperature is given by:
R
L
A
ρ = Resistivity: property of the material
(see reference tables)
L = Length of the wire
A = Cross Sectional Area of wire
L
A
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Example 1: A piece of aluminum wire used as an electric power line is 20.0 km long and 6.25 cm in diameter.
Find the resistance in the piece of wire.
Example 2: A 12.0 meter length of copper wire has a resistance of 1.50 ohms. How long must an aluminum
wire with the same cross-sectional area be to have the same resistance?
Example 3: A 0.500 meter length of wire with a cross sectional area of 3.14 x 10-6 meters squared is found to
have a resistance of 2.53 X 10-3 ohms. According to the resistivity chart what material could the wire be made
of?
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Name ______________________
Ph09_UnitPacket2014Key
Regents / Honors Physics
Date ____________
Guided Practice: Current and Resistance
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Name__________________________
Date_____________________
Regents Physics
Notes: Series and Parallel circuits
1.
2.
3.
4.
Define a series circuit and draw circuit diagrams for parallel circuits.
Define a parallel circuit and draw circuit diagrams for parallel circuits.
State the relationships for parallel circuits and solve problems using these relationships.
Compare and contrast series and parallel circuits.
Electrical Circuits
circuit
 Any path along which electrons may flow is a _______________________
Electric Circuit notation: (See Reference Tables)
straight lines and are taken
 Conductors -- Conductors are represented in electric circuits by solid, _________________
to be conductors of negligible resistance.
Devices --
electrodes
potential difference
 Cell – An electrochemical cell that has two ___________________ with a _____________________ for
electrons
Symbol
2 or more cells; is the source of potential difference in the circuit.
 Battery -- A combination of _______________
Symbol
conductor
 Resistor -- A device that is made of a relatively poor
________________________
of electricity. As current
voltage
flows through the PE of electrons is converted to heat energy. Results in a drop in ________________
Symbol
current
 Ammeter -- A meter that measures the ___________________
through a circuit or portion of a circuit.
through the meter in order to be
 The connections for an ammeter must force the current to flow _________________________
measured.
Symbol
potential difference between two points in a circuit.
 Voltmeter -- a meter that measures the _________________________
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two points
 A voltmeter must be connected to the ______________________
in the circuit where the potential difference
is to be measured.
parallel
 A voltmeter is connected in _______________________
Symbol
 A good rule to remember – If a voltmeter is connected so there is only _________
wire between the points where
the two leads are connected the voltmeter will read ___________
zero
 Light bulb -- As electrons flow through and collide with atoms heat is generated until a filament glows
bright.
Symbol
 Switch -- Used to interrupt or allow the flow of charge in a circuit.
Symbol
Example 1: Draw a circuit with one 9 volt battery and a resistor.
Example 2: Draw a circuit with a 9 volt battery and resistor using an ammeter to measure the flow of current.
Example 3: Redraw the circuit showing a voltmeter being used to measure the potential difference across the
battery.
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Example 4: In the following circuit do each of the following.
a. draw in an ammeter to measure the total flow in the circuit.
b. draw in a voltmeter to measure the potential difference across the battery.
c. draw in a voltmeter to measure the potential difference across the resistor.
d. draw in a voltmeter to measure the potential difference across the light bulb.
e.
Series Circuits
only one
 A circuit with ______________________
current path
connected to output of another component and back to battery until
 Input of one component is ____________________
loop is complete
current flow
 A break anywhere in the circuit results in stop of ______________________
Resistances in series circuits:
total resistance is the sum of all
 If resistances of components in a series circuit are known, _______________________
individual resistances
______________________________
Req = R1
+ R2 + R3 + . . .
Example:
Find RT in this circuit
Req = equivalent resistance
Rn = resistance of component n
R1 = 100 
R2 = 150 
V = 10 V
R3 = 200 
Equivalent circuits
Using Ohm’s law in a series circuit:
branches
 Find the current through the circuit. Note that since there are not _________________
in the circuit the
current is the same through all elements of the circuit
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Find the voltage drop across each of the resistors.
 Now that we know the current through each resistor we can use ohm’s law to find the voltage drop across
each resistor.
Parallel circuits
 A circuit where current has ____________________________
possible path to flow.
more than one
 Does not require all components ___________________________
for current to flow
be connected
remains constant
 Voltage across all components in parallel _________________________
may vary in different branches
 Current flow through components in parallel _______________
 To measure voltage, voltmeter leads are placed on opposite sides of any resistor
equivalent resistance can be found by:
 When resistors are connected in parallel, the _____________________________
1
1
1
1
 

...
Req R1 R2 R3
***To measure current, ammeter must be included in the loop***
Example problem: Assume in the circuit above R1 = 25 ohm, R2 = 35 ohm and R3 = 45 ohm. What is the
effective resistance of these three resistors? Draw the equivalent circuit to the one described here.
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Name________________________
Ph09_UnitPacket2014Key
Regents/Honors Physics
Date_____________
Notes: Kirchoff’s Laws
Kirchoff’s Laws
Loop Law

The ______________________
of voltages around any loop in a circuit is equal to _________
zero taking
total sum
batteries or other sources of potential difference as
positive
___________________
and resistors or other restrictive devices as
negative
_____________________.

The loop law is due to the law of conservation of
___________________
energy

greater energy
You cannot give charge ____________________________
in the
circuit
battery than it expends in the __________________.
Example:
Consider the equivalent circuit to the above with Resistors 1,2 and 3 combined into R123.
12 V -- _________
3V
________
--
2V
7V
___________
- ____________
=
0V
0V
Battery volts – R1 Voltage drop – R2 Voltage drop – R3 Voltage Drop = ___________________
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Junction Law
 A junction is any chosen point in a circuit.
flowing into a junction in a circuit is ________________
 The total current(s) _________________
the total current(s)
equal to
_____________________
flowing out of a junction in a circuit.
charge
 Kirchoff’s junction law is a consequence of the law of conservation of __________________.
 Charges cannot be ____________________
nor _______________________
at any location in the circuit.
created
destroyed
 Therefore __________________________.
Iin = Iout
Example:
Consider point “A” in the circuit above.
A
A
Compare the current flowing into point “A” to the sum of the currents flowing out of “A”
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Name ______________________
Ph09_UnitPacket2014Key
Regents / Honors Physics
Date ____________
Independent Practice: Combined Circuits
1. The circuit depicted in the diagram above is a (series) (parallel) circuit.
a. Explain how you know which type of circuit it is.
b. Draw a diagram that shows all elements in this circuit using the circuit symbols in your reference
tables.
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6. A 12 Ω and an 18 Ω resistor are connected to a 48-V power source.
a. What is the equivalent resistance of the circuit if the resistors are connected in series?
b. What is the equivalent resistance if the resistors are connected in parallel?
c. Draw the circuit diagram. Include in your diagram the minimum number of ammeter(s) that will
measure the current through EACH of the resistors and the minimum number of voltmeters that
will measure the voltage across EACH of the resistors.
7. A circuit is constructed as shown in the figure below. The voltmeter reads 63.0 V
a. Calculate the current through the 36 Ω resistor.
b. What is the voltage drop across the 42Ω resistor? . . . 54Ω resistor?
c. Which resistor dissipates the most energy per second?
d. What is the voltage of the power source (Hint: use Kirchoff’s loop law)?
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8. Referring to the circuit in the above diagram.
a. Determine what the equivalent resistance is.
b. Determine the current flowing through each resistor.
c. Determine the voltage drop across each resistor.