Chapter 17 and 18 Notes Mr. DePriest

Day One –Exploring Electrical Potential Energy Purpose Students will understand that: An object doing work against a field (gravitational or electrical) results in a gain in potential energy (electrical or gravitational). Whether a charge is doing work against an electric field depends on the direction of the electric field and the sign of the charge. Zero work is done when the displacement is perpendicular to electric or gravitational field lines.

Do Now – Write, Pair, Share. Pick up an activity sheet on the stool at the front of the room. Write down anything you remember about gravitational potential energy (GPE) and gravitational fields in the Venn diagram. Get a book if you need help remembering…the index is useful here! Things to think about: When does the GPE of an object increase? Decrease? Remain the same? Why does something have GPE? How did it obtain this energy? After a few minutes, talk about your answers with your desk partner. Be prepared to share and discuss!

Changes in Gravitational Potential Energy

Changes in Electric Potential Energy

Electric Potential Energy vs. Gravitational Potential Energy Electric potential energy in a uniform electric field PE electric = qEd along field lines! ΔPE electric = qEΔd along field lines! Gravitational potential energy in a uniform gravitational field PE gravitational = mgh along field lines! ΔPE gravitational =mgΔh along field lines! qEdqEd mghmgh Towards negative! Away from positive! Always towards Earth! Work = Fd along field lines Positive displaced parallel to field lines Negative displaced antiparallel to field lines

Electrical Potential Energy Units PE electric = qEd along field lines! PE electric another type of mechanical energy (other types?) PE electric depends on the charge. Coulombs Newton/ Coulomb Meters (Coulombs)* (Newton/Coulomb)* (Meters) = Newtons*Meters = Joules

Electric Potential

Homework “Let's Make an "Electron Gun” eading/index06.html eading/index06.html Page 587 problems 2, 5, 8 a, b

Exit Slip 1. What’s the difference between electric potential energy and electric potential? (Hint: think of the units!) 2. If a positive test charge is moved from Point A to Point B, How does its potential energy change? A negative test charge? 3. If it (the charge) took the blue path, how would your answer to question 2 change? 4. What is your preferred learning channel?

Day Two – What is a Battery and How Does it Work? Purpose Students will understand that: Batteries are a device that convert chemical energy into electrical energy by creating a separation of charges, and thus a potential difference. Batteries drive the current in a circuit. Batteries are analogous to charge escalators. They give the electrons energy by lifting it through a potential difference.

Do Now How or why does a battery power the electronics of our everyday lives? (Hint)

Battery Basics- A charge escalator Cathode (Cu/Oxygen) – Wants electrons compared to Al. ANODE (Al)- Doesn’t want electrons compared to Cu/Oxygen. Electrolyte (salt water in our battery) – Transports electrons from cathode to anode One metal wants electrons and the other doesn’t. This difference in want….and charge is what creates the potential difference.

Details of the Electrochemical Cell

A Difference in Want – Before the Wire is Connected Two reactions are occurring : One in the water near the copper wire (reduction) One at the aluminum foil (oxidation) These reactions create a build up of charge at each end Connecting the wires to the two electrodes allows the flow of electrons from one end to the other Electrons move against the field within the electrolyte (the salt water) This is what gives them the energy they need to power the circuit!!!

Homework Review Questions about the homework? A Capacitor!

A Battery Does Work

Homework/Exit Slip How does a battery provide energy in an electrical circuit? Is current “used up” by the lightbulb in the circuit?

Do Now Have a seat and be prepared for a demo!

Day three – How Are Current, Voltage, and Resistance Related? Purpose Students will understand that: The necessary components to create a working circuit are a power source, and a closed conducting loop. Parallel and series circuits operate under a different set of “rules” from each other. Students will be able to: Build simple series and parallel circuits with batteries, switches, and lightbulbs Draw schematics of simple series and parallel circuits with batteries, switches, and lightbulbs

Requirements of a Simple Circuit?

Light Bulb Anatomy The anatomy of a light bulb allows a closed conducting loop from the positive to the negative terminal of the battery, or vice versa.

Which ones lit the light bulb? Electrons take the path of least resistance*!

Current What are the blue dots? Explain your reasoning. Electrons. They move from the negative terminal to the positive terminal of the battery. Current – The amount of charge passing a given cross sectional area per unit time

Current – Denoted by the symbol I Flow of electrons (negative charge) Direction of conventional current

Current – Flipping a switch Does it take time for a light to illuminate a room when you flip a switch? NO!!! (…well pretty much) Does this mean the electrons move at very fast speeds from the switch to the lightbulb? NO!!! A current of 10.0 A (10 C/s) means the electrons are moving with a drift speed of roughly.25 mm/s!

Ohm’s Law Ohmic Material Non-Ohmic Material

Resistance of a Material Resistance depends on: The material Some conductors allow charges to flow more easily than others The length of the material The longer the wire, the more collisions the elctrons will undergo, and thus more resistance The width of the material. The wider the material, the more space the electrons have to move.

Potentiometers – Resistance depends on length Most things are designed to have a fixed resistance, but a potentiometer (or Pot for short) has a variable resistance that the user can control. The design takes advantage of the fact that resistance depends on the length of the material. In everyday devices such as the volume control in your car radio, and light dimming switches.

Resistance (to Current) in Circuits Series Circuits All the current has to run through all the resistors in a series circuit. Parallel Circuits All the current is split between each “branch” in the circuit

Applying Ohms Law (V= IR) How much total current is present in the circuit ( with a 1.5 V battery) if the lightbulb has a resistance of 10 Ω?

Homework – Optional and HIGHLY Recommended Page 602 problems 1,3,4,9 Page 601 problems 3 (a)(b), 4, 5

Exit Slip (A)(B) (C) (D) (E) In each circuit (A,B,C,D, and E) rank the brightness of the lightbulbs using >, <, and = signs

Do Now (A)(B) (C) (D) (E) In each circuit (A,B,C,D, and E) rank the brightness of the lightbulbs using >, <, and = signs

Day Four – Series Circuits Purpose Students will understand that: The sum of the voltage drops across individual resistors in series is equal to the voltage drop across the battery or other EMF source. The current through resistors in series are all equal and the voltage across parallel branches are equal. Resistors add in series to give the total resistance of the circuit while resistors in parallel add reciprocally Students will be able to: Reduce a circuit in series and parallel

How to Analyze Circuits with Resistors in Series a b c d e f g h 60V 30V 0V a b c d e f g h a b c d 60V 30V 0V a b c d

Adding Resistors in Series R eq = R 1 + R 2 + R I battery = I 1 = I 2 = I 3 = ΔV battery / R eq ΔV battery = ΔV 1 + ΔV 2 + ΔV Current is the same through all resistors

How to Analyze Circuits with Resistors in Parallel 1/R eq = 1/R 1 + 1/R 2 + 1/R 3 + = 1/3Ω + 1/6Ω + 1/12Ω = 7/12 Ω R eq = 12/7 Ω I Total = I 1 + I 2 + I 3 = ΔV battery / R 1 + ΔV battery / R 2 + ΔV battery / R 3 = 12 V / 3 Ω + 12V/6 Ω + 12V/12 Ω = 4 A + 2 A + 1 A = 7 A ΔV battery = ΔV CD = ΔV EF = ΔV GH Ω 6 Ω 12 Ω 12 V a b c d 4 A 2 A1 A 12V 7 A

Parallel Circuit Equations 1/R eq = 1/R 1 + 1/R 2 + 1/R I total = I 1 + I 2 + I 3 = ΔV battery / R eq ΔV battery = ΔV 1 = ΔV 2 = ΔV 3 =... Voltage is the same across all branches in a parallel circuit.

Integrated Circuits – Semiconductors, diodes, and transistors

Set up for parallel circuit

Homework – Optional and Highly Recommended Page 638 problems 1 (a)(b) 2(a)(b)(c) 4(a)(b) Page (Explain your answer) 3 (a)(b) 5 If applicable to the problem, draw the schematic of the diagrams in your circuit

Exit Slip (A)(B) (C) (D) (E) In each circuit (A,B,C,D, and E) rank the brightness of the lightbulbs using >, <, and = signs