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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


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

Water will spontaneously flow from a reservoir of ______________________ to a reservoir of

____________________

Similarly electric charges will spontaneously flow from a place of ________________ potential to a place of

________________ potential they can do work.

Consider two oppositely charged plates:

An electron has higher potential energy at the negatively charged plate and can ____________________ as it

falls from the place of higher potential to the place of lower potential.

Providing a ______________________ 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

per__________________.

+

+ +

+

+ +

-

- -

-

-

Place of _______ potential for electrons

Place of __________ potential for electrons

-

- -

-

higher

lower higher

lower

do work

coducting wire

electric charge

unit time

higher pressure

lower pressure


In the language of mathematics:

t

qI

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

Very often when charge is flowing it is the result of flow of __________________

Charge may also flow as a result of _________________________ flowing

Consider a positive and negative charge with a potential difference

By convention current is considered to flow in the direction of ______________________ in elecric circuits.

(Opposite direction of __________________)

I = current (amperes = coulomb/second) Q = charge (coulomb) t = time (seconds)

+

Direction of electron flow

Flow of ____________ charges

electrons

charged ions

positive charges

electrons

positive


Sources of electrical energy

Batteries -- Chemical reactions cause _______________________ with a potential difference.

Electrons spontaneously flow from ___________________ to ______________________.

Generators -- Mechanical energy in a ______________________ is converted to an electrical potential

difference.

Resistance to Charge Flow

Water being pumped through a hose may experience resistance due to ________________ if it were forced

to travel through a zig-zag hose.

Flowing electric charges usually do work because of _______________________ that they experience when

trying to flow.

Ex: Electrons flowing through a ________________________ have lots of collisions with atoms, make

them hot until they glow. (incandescent light)

Resistance for a given piece of wire depends on the:

o ________________ of the wire; A longer wire has _________________ resistance.

o ________________ of the wire: a fatter wire has ___________ resistance.

o __________________ of the wire; a hotter wire has ____________ resistance.

o the __________________ of the material that the wire is made of; e.g. gold is a better conductor

than ____________________

The resistance of a given piece of wire at a given temperature is given by:

resistance

tungston wire

negative pole positive pole

charged poles

magnetic field

friction

length greater

diameter greater

temperature greater

properties

aluminum

A

LR

ρ = Resistivity: property of the material (see reference tables) L = Length of the wire

A = Cross Sectional Area of wire

A L


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?


Name ______________________ Regents / Honors Physics

Date ____________

Guided Practice: Current and Resistance


Name__________________________ Regents Physics

Date_____________________

Notes: Series and Parallel circuits

1. Define a series circuit and draw circuit diagrams for parallel circuits.

2. Define a parallel circuit and draw circuit diagrams for parallel circuits.

3. State the relationships for parallel circuits and solve problems using these relationships.

4. Compare and contrast series and parallel circuits.

Electrical Circuits

Any path along which electrons may flow is a _______________________

Electric Circuit notation: (See Reference Tables)

Conductors -- Conductors are represented in electric circuits by solid, _________________ and are taken

to be conductors of negligible resistance.

Devices --

Cell – An electrochemical cell that has two ___________________ with a _____________________ for

electrons

Symbol

Battery -- A combination of _______________ cells; is the source of potential difference in the circuit.

Symbol

Resistor -- A device that is made of a relatively ________________________ of electricity. As current

flows through the PE of electrons is converted to heat energy. Results in a drop in ________________

Symbol

Ammeter -- A meter that measures the ___________________ through a circuit or portion of a circuit.

The connections for an ammeter must force the current to flow _________________________ in order to be

measured.

Symbol

Voltmeter -- a meter that measures the _________________________ between two points in a circuit.

circuit

straight lines

electrodes potential difference

2 or more

poor conductor

voltage

current

through the meter

potential difference


A voltmeter must be connected to the ______________________ in the circuit where the potential difference

is to be measured.

A voltmeter is connected in _______________________

Symbol

A good rule to remember – If a voltmeter is connected so there is only _________ between the points where

the two leads are connected the voltmeter will read ___________

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.

two points

parallel

wire

zero


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

A circuit with ______________________ current path

Input of one component is ____________________ output of another component and back to battery until

loop is complete

A break anywhere in the circuit results in stop of ______________________

Resistances in series circuits:

If resistances of components in a series circuit are known, _______________________ is the sum of all

______________________________

Req = R1 + R2 + R3 + . . .

Example:

Find RT in this circuit

Using Ohm’s law in a series circuit:

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

Req = equivalent resistance

Rn = resistance of component n

R1 = 100

R3 = 200

R2 = 150 V = 10 V

Equivalent circuits

only one

connected to

current flow

total resistance

individual resistances

branches


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.

Does not require all components ___________________________ for current to flow

Voltage across all components in parallel _________________________

Current flow through components in parallel _______________ in different branches

To measure voltage, voltmeter leads are placed on opposite sides of any resistor

When resistors are connected in parallel, the _____________________________ can be found by:

...1111

321

RRRReq

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.

***To measure current, ammeter must be included in the loop***

more than one

be connected

remains constant

may vary

equivalent resistance


Name________________________ 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 _________ taking

batteries or other sources of potential difference as

___________________ and resistors or other restrictive devices as

_____________________.

The loop law is due to the law of conservation of

___________________

You cannot give charge ____________________________ in the

battery than it expends in the __________________.

Example:

Consider the equivalent circuit to the above with Resistors 1,2 and 3 combined into R123.

________ -- _________ -- ___________ - ____________ =

Battery volts – R1 Voltage drop – R2 Voltage drop – R3 Voltage Drop = ___________________

total sum zero

positive

negative

energy

greater energy

circuit

12 V 3 V 7 V 2 V 0 V

0 V


Junction Law

A junction is any chosen point in a circuit.

The total current(s) _________________ a junction in a circuit is ________________ the total current(s)

_____________________ a junction in a circuit.

Kirchoff’s junction law is a consequence of the law of conservation of __________________.

Charges cannot be ____________________ nor _______________________ at any location in the circuit.

Therefore __________________________.

Example:

Consider point “A” in the circuit above.

Compare the current flowing into point “A” to the sum of the currents flowing out of “A”

A A

flowing into equal to

flowing out of

charge

created destroyed

Iin = Iout

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&uact=8&docid=kLbD3OyMah_U-M&tbnid=Ch9r_ka4zMLqmM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.physics.byu.edu%2Ffaculty%2Fchristensen%2FPhysics%2520220%2FFTI%2F28%2520DC%2520Circuits%2F28.11%2520Kirchoff's%2520Junction%2520Rule.htm&ei=3uIxU-CZMI3I0AHwpYCgAg&bvm=bv.63587204,d.dmQ&psig=AFQjCNHY07ggFcl4ZTW1A3Slh0FAuuyc-A&ust=1395864663050185


Name ______________________ 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.

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&uact=8&docid=jXq5GwTaWrhrAM&tbnid=BxVqq9VrNIuNXM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.teachengineering.org%2Fview_activity.php%3Furl%3Dcollection%2Fcub_%2Factivities%2Fcub_electricity%2Fcub_electricity_lesson05_activity1.xml&ei=c9EyU-G9KPTNsASbqoDoAw&bvm=bv.63738703,d.eW0&psig=AFQjCNGyHuBeDyl6U179gZ6rFP2TdxhIrQ&ust=1395925648796284


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)?


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.

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