Warm-Up: April 11, 2016  5.10x10 -4 C is stored in a capacitor that has a capacitance of 9.52x10 -7 F. What is the electric potential difference in the capacitor? 536 V

Homework Questions?

Quiz This Week?  Maybe, so be ready for one…  Could be a quiz on Chapters 20 and 21  Could be a binder-check quiz  Could be a units quiz with the new units

Extra Credit Opportunity  Write an essay on a physicist whose work we have discussed in class, other than Newton  Essay must be at least 3 pages, typed, double spaced, point font.  Essay will be graded on content and proper English.  Essay is worth up to 20 homework points of extra credit (currently 5-6% of overall grade)  Essay is due May 30

Possible Physicists  Robert A. Millikan  Galileo Galilei  Willebrod Snell  Christiaan Huygens  Robert Hooke  Benjamin Franklin  Henry Cavendish  Charles Augustin de Coulomb  James Watt  Count Alessandro Volta  Andre Marie Ampere  Johann Carl Friedrich Gauss

Possible Physicists  Hans Christian Oersted  Sir David Brewster  Augusten-Jean Fresnel  Georg Ohm  Michael Faraday  Felix Savart  Heinrich Hertz  Sadi Carnot  Joseph Henry  Christian Doppler  James Prescott Joule  Hermann von Helmholtz  Rudolf Clausius  and many others…

Choice of Physicist  No repeats allowed (between all of Mr. Szwast’s physics classes)  Mr. Szwast with your choice after 11:30 AM today. All requests are first- come, first-serve.

Essay Requirements  Must include biographical information (place/time of birth, major life events, etc.)  Must include notable work Include things we have not discussed in class  Must describe how his/her work relates to what we have learned in this class  Must be detailed  Must use proper English  Must have proper MLA formatting Including citations and works cited page

More Essay Details  Essays are due May 30, but may be turned in earlier.  Essays will be graded in the order submitted.  Should have at least 10 citations from at least 3 different works.  It will take an amazing essay to get all 20 points.  A very good essay will be worth ~10 points

Chapter 22

About ΔV  We know that only differences in electric potential can be measured, which is why we use Δ  In further equations, we’re going to skip writing the Δ, understanding that it’s still a difference

Flow of Positive Charges

Electric Current  A flow of charged particles is an electric current.  Conventional current is the flow of positive charges. In reality, it is negatively charged electrons flowing in the opposite direction.  Conventional current flows from high electric potential to low electric potential.  Current is measured by an ammeter.

Electric Current

Example 1  A circuit has a current of 37 mA. How much charge passes through a point in the circuit in 15 seconds? 0.56 C

You-Try #1 a) A circuit has a current of 52 mA. How much charge passes through a point in the circuit in 37 seconds? b) If the current is from flowing electrons, how many electrons pass through the point in those 37 seconds? 1.9 C 1.2x10 19 electrons

Electric Energy  The electric energy carried in a circuit is the amount of charge transferred multiplied by the electric potential difference across which it moves.  Measured in Joules

Sources of Electricity  A voltaic cell (or galvanic cell) converts chemical energy into electric energy  A collection of voltaic cells connected together is a battery.  A photovoltaic cell (or solar cell) converts light energy into electric energy.  A generator converts mechanical energy into electric energy.

Electric Circuits  Any closed loop or conducting path that allows electric charges to flow is called an electric circuit.  Must contain something that creates electric energy, and something that consumes it.

Warm-Up:  In exactly one minute, 4.82x10 -2 C pass through a circuit. What is the current that is flowing through the circuit? 8.03x10 -4 A

Homework Questions?

Electric Power  The electric power is the rate at which electric energy is created or used  Equal to the current times the electric potential difference  Measured in Watts, W

Example 2  The current through a light bulb connected across the terminals of a 125 V outlet is 0.50 A. At what rate does the bulb convert electric energy to light and heat? 62 W

You-Try #2  A car battery causes a current of 2.0 A through a lamp and produces 12 V across it. What is the power used by the lamp? 24 W

Resistance

Ohm’s Law  Resistance equals electric potential difference divided by current

Example 3  An automobile panel lamp with a resistance of 33 Ω is placed across a 12 V battery. What is the current through the circuit? 0.36 A

You-Try #3  A motor with an operating resistance of 29 Ω is connected to a battery. The current in the circuit is 3.8 A. What is the electric potential difference of the source? 110 V

Assignments  Read Chapter 22  Page 610 #39, 44-45,  Page 610 #38, 53-57, 82-85,  Optional advanced reading: OpenStax Chapter 20

Warm-Up: April 12, 2016 a) In exactly one minute, 4.82x10 -2 C pass through a circuit. What is the current that is flowing through the circuit? b) How many electrons flow through a portion of the circuit every second? c) If the current is produced by a 12.0 V battery, what is the electric power produced by the battery? 8.03x10 -4 A 5.02x10 15 electrons 9.64x10 -3 W

Homework Questions?

Resistors  A resistor is a device made to have a certain resistance.  Resistors are used to control the amount of current in a circuit.  A material with zero resistance is called a superconductor.

Changing Resistance (page 595) Increase resistance by:Decrease resistance by:  Increasing length  Decreasing cross-section  Increase temperature  Use a material with higher resistance  Decreasing length  Increase cross-section  Decrease temperature  Use a material with lower resistance

Binder Quiz!  10 minute time limit  If you appear to be talking, you will receive a zero.  If you appear to be looking at anyone else’s paper(s), you will receive a zero.  No retakes on binder quizzes.  Put your binder quiz face down in front of you when you finish.

Circuit Diagrams  Use standard symbols for circuit components – see page 597

The Symbols We Will Use

Circuit Diagram Examples

Power Dissipated in a Resistor  We can combine Ohm’s Law with our previous formulas to get two new formulas:

Thermal Energy Created

Example 4  An 18 Ω heater operates on a 120 V outlet. a) What is the current through the heater? b) How much power is used by the heater? c) How much thermal energy is liberated in 30.0 s? I = 6.7 A P = 8.0x10 2 W TE = J

You-Try #4  A 34 Ω resister is connected across a 45 V battery. a) What is the current through the resistor? b) How much power is dissipated in the resistor? c) How much thermal energy is liberated in 2.0 minutes? I = 1.3 A P = 60. W TE = 7100 J

Assignments  Read Chapter 22  Page 610 #39, 44-45,  Page 610 #38, 53-57, 82-85,  Optional advanced reading: OpenStax Chapter 20