Most of my students in AP Physics 1 struggle with unit tests for a good part of the year. There are lots of reasons for this, including a lack of previous experience with physics, the difficulty of the material, and the difficulty of the tests. I do attempt to make each unit test model a mini version of the AP Exam. When a student does poorly on one of these exams, they often panic. Many are students who are used to making As in everything. They have usually done very well on tests. They don’t really have a recovery strategy when they bomb a test. This year is no different, and perhaps a bit worse due to virtual/hybrid instruction and a reduced class time. I have a lot of students struggling with tests.
To help out those students who bomb a test, I came up with “Second Chance Exams,” inspired by my previous experimentation during face-to-face instruction with “2-Stage Exams.” I learned about 2-stage exams from this article by Carl Weiman (Nobel Prize winner in Physics (and founder of the PhET Sims site) and others:
The article was published in The Physics Teacher. If you teach physics and you haven’t joined the American Association of Physics Teachers, go ahead and join today.
Here is my own summary of how I implemented the original approach. First you write your unit test, the “Stage 1 Exam.”. Mine are usually 10 multiple choice questions and then one or a couple of free-response questions. The source of the questions is usually old AP Physics B questions modified to be more like AP Physics 1 (make them more conceptual than calculation). I also use questions I wrote myself from scratch, and a few questions modified from other sources to be AP1-like material. The grades are scaled so that they approximate the distribution of points that corresponds to an AP Exam score. Even with the scaling, some students make a panic-inducing score.
I construct a “Stage 2 Exam” by taking some of the most-missed questions from the original test and rewriting them. If they were already conceptual questions, I change them into slightly different questions. If they were mathematical questions, I typically modify them to be more conceptual. In both cases, I focus on the mistakes in understanding that students typically make on the Stage 1 questions.
Students take Stage 1, individually, in a typical manner (paper and pencil in my classroom, in a normal year). Then, immediately after they all finish (45 minutes to an hour into a 90 minute block), I pass out Stage 2, and students work together in their lab groups to complete that assignment as a group activity. Because of time limitations, I usually actually did Stage 2 at the next class period, although that is not the approach recommended in the original article above.
This 2-stage approach works well for building student understanding, and improves grades. The Exam score is 75% Stage 1 (individual score), 25% Stage 2 (group score).
In the current year, teaching Hybrid model, I came up with a different approach. Class time is greatly reduced. Many of my AP students are hybrid or full virtual and small-group collaboration is more difficult. I write and score the Stage 1 version of the exam in the same way, but I have been administering it online, using Canvas. For the second stage, I did something similar to what I describe above. I wrote a largely conceptual second stage as a Google Doc. I distributed it to the students who made a score of less than 80% on the first exam via Google Classroom. Students have to answer all of the questions to my satisfaction on the Google Doc to earn a replacement score of 80% on the Stage 1 test. Once they submit their work, I comment on what they wrote and return it to them. I only enter a grade if they complete the whole assignment to my satisfaction. Otherwise the Stage 1 Test Score remains the same. Students are allowed to work with a partner(s), look things up, or ask me questions. I do have lots of conferences (face-to-face and via Zoom) with students who submitted Stage 2, but still are stuck on some of the questions. Of course, some students ignore the whole process and just let their test scores remain low. Despite that, the system does seem to be working. It relieves a lot of the panic. I can focus students on their errors of understanding. They are encouraged to reach out directly to me when they don’t understand a second (or even a third) time. And the Stage 2 tests are relatively easy to grade.
Here is part of a “Stage 1” Free Response question (modified from an old AP Physics B exam question):
And here is the “Stage 2” version: (I just noticed I did go ahead and ask the same question twice, probably because I saw so many calculation errors on what was supposed to be a review question)`
Here is an original Stage 1 question that was conceptual
And below is a Stage 2 version of the same question:
Here is a summary of my online version changes from Weiman Model:
Reif 2nd Chance version
Original Weiman 2-Stage
Optional, by invitation (test score <80%)
During class, immediately after exam
Students worked individually or with partner
Small group activity
Successful completion raised grade to 80%
Exam score combination of 75% Stage 1 Score and 25% Stage 2 Score
My 2020 Online version is really a kind of modified test corrections. It seems to me to have advantages over test corrections:
1. The questions are new, so students can’t just ask somebody who got it right the first time.
2. I can focus the questions on what the students didn’t understand, based on what they wrote on the first test.
3. The Stage 2 Tests are much easier and quicker to grade than test corrections. Everybody is answering the same questions. Everybody’s assignment is the same length. I can write an assignment of the length I want to grade, rather than grading everything that the student needed to correct.
This instructional technique increases student engagement (they ask if they have a question for the day when they come in!), allows them to practice their argumentation skills (Science Practice 6, Argumentation), and can increase understanding of the basic concepts.
2. Students answer individually (no discussion) and anonymously
3. Students view a graph of the class’s responses
4. Students discuss with each other how they responded and why. They try to reach consensus with their discussion partners.
5. Students answer the same question again.
6. The class views the responses and the teacher leads a consensus-building discussion
The way I have used it, Peer Instruction depends on students discussing face-to-face, but how do you do that with a hybrid or online environment?
One short answer is that you can do this with PearDeck.com. This is an add-on to Google Slides. It allows you to add many types of questions to a Google Slide. The students join a Pear Deck session, view the question, and enter their responses. You can then show the graph of student responses from Pear Deck, and go through the sequence above. You need to have made a slide show with the same multiple choice question in it twice. Here is an example of a Pear Deck Slide show for a Paul Hewitt Next-Time Question.
If you don’t want to use Pear Deck, or you want to try and get the effect of Peer Instruction asynchronously, I did read about a way to use Peer Instruction online without live interaction. In The Physics Teacher journal online, I read this article, Peer Tutoring in Web-based Concept Tests. The authors used LON-CAPA to collect student justifications along with their responses. Instead of interacting live, the students can view other’s justifications.
A modification of this involves providing simulated interactions. You would present the multiple choice question, have students answer, then have them view student statements about the question and the choices. Then, after the simulated interaction, they vote again.
Science teachers want students to think like scientists, write like scientists, and investigate like scientists. Writing has special prominence in AP Physics 1 and 2.
In order to learn to write like a scientist, students have to practice writing, get feedback, respond to the feedback, and revise their writing. Using an LMS and a few simple guiding principles can make that writing-feedback-revising cycle work in the classroom.
The Covid-19 Pandemic has caused a lot of changes in the lives of teenagers and their teachers this spring. School for us closed on March 12, and we went to online instruction through Google Classroom and Zoom meetings. The College Board elected to make all AP Exams online, 45 minute exams. The AP Physics Exams this year consisted of only two free-response questions. The questions could be answered completely by typing. None of the questions required drawings, diagrams, graphing, or derivations. In previous years, all of these tasks were very important parts of the AP exams. I spent a lot of time last year training my students to do them. Now, they were going to write about the tasks, and they were free to use notes, textbooks, or Google to help them answer the questions.
So, I changed the way I wrote my assignments. I turned drawing free-body diagrams into “describe the forces” and “calculate” into “does this equation make sense”? And I changed the way I assessed assignments. I instituted a new grading scheme. I commented on every part of every assignment. Relatively flawless work earned a 100%. Students whose work had major flaws were allowed to revise and resubmit multiple times. If a student didn’t get the work up to my standards, they earned a 60%.
This system worked very well. Rather than checking for right answers, I was looking for correct understanding. Instead of getting a grade, students were getting feedback and felt compelled to respond to the feedback. It sometimes took a couple of tries for the student to get it right, but they did improve.
So, I came up with some guidelines that worked for this grading scheme:
Make short writing assignments, 10 questions or fewer. One page is ideal (no scrolling).
Assignments involve explaining a physics idea or ideas in words.
Make all the assignments in an easy to grade format in Google docs.
Give directions to the students for their response “Type your coherent, paragraph-length response in this box”.
Use your judgment as to whether the answer is good enough. Make a rubric or scoring guideline before grading, to make sure that you are consistently grading.
If a student misstates, misinterprets, or doesn’t use one of the ideas in a correct response, they must correct their answer
Give students low grades (60%) and demand corrections before improving the grade.
Write comments on each response to show them how to correct.
If the corrections are not correct, write a more directed comment and ask them to redo. If there are lots of mistakes on a longer document, pick only the most important questions and only demand that they redo those.
Grade fast so they can work on their modified response right away.
Here is an example of an assignment I wrote. Students learned this topic virtually. Below is the stem and the stimulus for part (a).
And here is the stimulus for part (b).
Below is a student’s modified answer to part (a) with my original comment. The blue check mark means that the comment was marked as resolved. The first attempt earned a grade of 60:
And below is the same students modified answer to part (b) with my original comment:
And here are the general comments between student and teacher.
Yes, the Google Classroom Learning Management System (LMS) makes this easier, but it could be done without it, using Microsoft Word’s reviewing features, for example.
The assignments were short, students knew they had the opportunity to revise and the feedback was (relatively) swift. A number of them seemed to improve in their writing as we went through the process of reviewing for the AP1 exam.
For 2020-2021 The students in AP Physics 1 will have had no previous physics course. Most had Pre-AP Biology or Pre-AP Chemistry in the previous your. Many are concurrently enrolled in PreCalculus, some in AP Calculus (usually AB), and a few will be in Algebra II or III.
Instruction begins on Friday, 13 August 2020 Our school is on A/B/C block. Each class meetings two 82-minute sessions (A/B) and one 42-minute session (C) every week. We have about 160 meetings before the AP Exam. There are about 34 A/B meetings and 13 C meetings in the first semester and 31 A/B meetings in the second semester and 12 C meetings before the AP1 Exams. That is 6380 minutes or 106 hours or 4.4 complete days of instruction. So, first semester 47 actual class meetings and second semester 43 actual class meetings. 90 days of instruction before the exam.
Text Eugenia Etkina College Physics 2nd Edition
Note: Observational Experiments derive physics from a series of observations. Testing Experiments test a hypothesis.
Conservation of mass, Conservation of linear momentum in one (quantitative) and two dimensions ( semi-quantitative), impulse
Paradigm Labs Observational Experiment: Modeling Collisions of Carts; Observational Experiment: Modeling Impulse and Change in Momentum
Oct 1 – Oct 16
Unit 05 Energy Transfer Model
Work as energy transfer, models for energy storage, energy dissipation, energy and collisions
Paradigm Labs Testing Experiment: Hooke’s Law and Elastic Energy Testing Experiment: Transfers to Kinetic Energy
19 Oct – 3 Nov
Unit 06 Models for 2d Motion
Section 4.5, Chapter 5
Kinematics and dynamics of projectile motion, Uniform Circular Motion, Universal Gravitation and Orbits
Paradigm Lab Observational Experiment: Projectile motion video analysis Observational Experiment: Behavior of objects in Circular motion
4 Nov – 4 Dec
Unit 07 Models for Rotation
Chapters 8 and 9
Torque and Semi-quantitative Rotational Statics; Rotational Kinematics, Newton’s Second Law for Rotation, Rotational Momentum, Rotational Kinetic Energy
Paradigm Labs Observational Experiment: Balanced Torques Testing Experiment: Acceleration of a wheel
6 Jan – 29 Jan
Unit 08 Models for Oscillation
Kinematics, dynamics, and energy models for mass-spring oscillator and pendulum
Paradigm Lab Testing Experiment: Period of a Mass-Spring Oscillator
1 Feb to 12 Feb
Unit 09 Mechanical Waves and Sound
Wave pulses, traveling waves, standing waves, sound Paradigm LabsObservational Experiment: Wave PulsesTesting Experiment: Speed of Wave Pulses on a String
16 Feb to 12 Mar
Unit 10 Electric Charge and Force
Conservation of charge, Coulomb’s Law
Paradigm LabObservational Experiment: Sticky tape
3 meetings (no test)
Unit 11 DC Circuits
Resistivity and Resistance, Ohm’s Law, Kirchhoff’s rules
Paradigm Lab Observational Experiment:Potential difference in circuits
29 Mar-15 Apr
NOTE: This is maybe not enough review, but don’t see how to go faster.
AP 1 Exam on Tuesday, 5 May 2021
This sequence doesn’t EXACTLY follow the Unit Guides in the College Board’s AP Physics 1 Course and Exam Description. If next year, as they did this year, the College Board cuts off the last unit or more, I will have to flip Units 10 and 11 with Unit 9.
Even as I post this, I’m two weeks behind!! The Governor of Arkansas has pushed the first day of school back to August 24 due to the community spread of the Covid-19 virus in Arkansas.
For 2020-2021 The students in AP Physics C have about half had AP Physics 1, about half have not. Most (I think) are enrolled in AP Calculus AB or BC.
Instruction begins on Friday, 13 August 2020 Our school is on A/B/C block. Each class meets two 82-minute sessions (A/B) and one 42-minute session (C) every week.
We have about 160 meetings before the AP Exam. There are about 34 A/B meetings and 13 C meetings in the first semester and 31 A/B meetings in the second semester and 12 C meetings before the APC Exams. That is 6380 minutes or 106 hours or 4.4 complete days of instruction.
So, first semester 47 actual class meetings and second semester 43 actual class meetings. 90 days of instruction before the exam.
Text Randall Knight, Physics for Scientists and Engineers, A Strategic Approach, 4ed
Unit 01 – Tools Text Chapter 3 (vectors)
Vectors (including unit vectors), Graphical Analysis, Measurement and uncertainty, Scientific method, Calculus concepts and elementary methods.
A paradigm is a “model, pattern, example, exemplar, template, standard, prototype, archetype.” In modeling instruction, they are typically a demonstration or lab setup that serves to focus student attention on what is important in the unit. Paradigms are presented as the subject of a student-designed lab that is usually done at the beginning of the unit, and serves to help develop the conceptual model(s) for the unit.
If in-person school is not possible, I intend to make short videos showing the data collection of each lab. Students will “collect” the data from the video and analyze it at home.
Next year I will be teaching Mechanics as a full-year course, so there should be enough time to do all (or at least most) of these labs.
Lab 1 – Introductory lab – Three linear paradigms in one lab
Constant Velocity Model – Blinky Buggy toy moves with constant velocity
Constant Acceleration Model (possibly with vectors) – Physics Fan cart moves with constant acceleration. Fan may be modified by changing angle and speed.
Non-constant Acceleration Model – Sliding Chain (over a pulley) breaking the constant acceleration model.
Lab 2 – Another paradigm later on:
Circular Motion Model – (The Knight Textbook works a bit of circular motion into 2-d kinematics) – Rotating wheel slowing with constant acceleration. Probably use a Vernier Rotary Motion Sensor with an attachment. Another possibility is a bicycle wheel.
Unit 2: Newton’s Laws of Motion
Lab 3 – Introductory lab
Constant Net Force Model – Fan Cart (with fan directed at angles for vectors). Develop Newton’s Second Law.
Labs 4 and 5 – Later on
Connected Objects Model – Atwood’s Machine, collect a data set using the materials from which the gravitational field strength of Earth can be derived.
Impulse-Momentum Transfer Model – Force-time during a collision and change in Momentum. Using dynamics carts, Vernier Bumper-Launcher Kit (and maybe Pasco Spring Cart Launcher)
Lab 9 – Later investigation
Modeling Collisions – Dynamics Cart collisions in one dimension
Unit 5: Rotation
Lab 10 – Introductory Lab
Extended Object Model – Rotational Inertia and Angular Acceleration. Vernier Rotary Motion Sensor and accessory kit again.
Unit 6: Oscillations
Lab 11 – Introductory Lab
Simple Harmonic Oscillator Model – Dependent variables that affect period/frequency of a mass-spring system. I like Pasco Springs for this. Equal Length and Hooke’s Law Set. They look the same, but are different:
Lab 12 – Later on
Physical Pendulum Model – Dependent variables that affect period/frequency of an extended object pendulum. Vernier Rotary Motion Sensor and Accessory kit, again.
Unit 7: Gravitation
Lab 13 – Introductory Lab
Universal Gravitation Model – Cavendish Balance (classroom demonstration, I don’t have the money to buy a balance that provides quantitative results). Thinking of either setting up my own for demo purposes, or showing the YouTube videos of other’s.
The clearest evidence that AP Physics and Modeling are a great fit is seen in the AP Physics Science Practices. These are embedded in each course, outlining the skills that should be developed by the students. Each AP Exam question incorporates one or more Science Practices. This is described in detail in the Course and Exam Description for each course. There is a set of SPs for AP Physics 1 and 2 (see below), and a slightly different set for AP Physics C Mechanics and Electricity and Magnetism.
In this post, I’ll take you through the Science Practices for AP Physics 1 and 2, and I’ll list one example of a connection with Modeling for each practice.
Science Practice 1, Modeling
“The student can use representations and models to communicate scientific phenomena and solve scientific problems”
What could be more clear! Science Practice #1 is “Modeling” and the Modeling Method for teaching physics is about training students to see science as the process of constructing conceptual models to explain nature.
In teaching with modeling, students begin most units by examining paradigms (standard examples) of each model in a student-designed lab. The students represent the behavior of the paradigm with four types of representations, mathematical, graphical, pictorial, and verbal. That means Science Practice 1 is embedded in every Modeling unit right from the start.
Science Practice 2, Mathematical Routines
“The student can use mathematics appropriately.”
In AP Physics 1/2 this Science Practice is often used to indicate an exam question that requires calculations by the student. But it is also used to indicate cases where a student has to explain WHY an equation (or a graph) makes sense, or why a representation models a physical situation. Here is an example from the 2019 AP Physics 1 released exam questions:
In teaching with Modeling, we use classroom discourse to accomplish the same ends. The teacher (and even other students) ask deep questions that cause students to justify the graph that they constructed, or the mathematics that they used to solve a problem. The whole class participates in this discussion, so that everybody understands WHY the techniques that were applied to create the model or solve the problem make sense. I wrote this blog post describing some of the popular whiteboarding techniques.
Science Practice 3, Scientific Questioning
“The student can engage in scientific questioning to extend thinking or to guide investigations within the context of the AP® course.“
This science practice has three components:
3.1 The student can pose scientific questions.
3.2 The student can refine scientific questions.
3.3 The student can evaluate scientific questions.
In teaching with modeling, many units begin with a student-designed “paradigm lab.” Teachers demonstrate an interesting system, the “paradigm” (a pendulum, in one unit), and students (with lots of guidance and some limitations) choose what they want to investigate about the physics of the paradigm. Students pose observations and questions about the system in a whole-class brainstorm. They refine the questions in deciding what variables to test and how they can test them. And they evaluate the questions in the model-building discussion that follows the lab, where students decide what their lab results mean.
Science Practice 4, Experimental Methods
“The student can plan and implement data collection strategies appropriate to a particular scientific question.“
On the AP exam, this is assessed in a question where students must design a lab to answer a question. In the modeling classroom, this is a component of nearly every unit. Modeling-trained teachers give students leeway to create and carry out their own labs. This is excellent practice for AP experimental questions.
Science Practice 5, Data Analysis
“The student can perform data analysis and evaluation of evidence.“
In modeling, students must frequently collect data, construct a table, graph the data, produce a mathematical model that represents the data (and the physical system), and then explain in their whiteboard presentation their whole process and findings.
And here’s an example of how the AP Exam assesses the skills developed from teaching with inquiry and modeling, also from the 2019 AP Physics 1 Free Response questions:
Science Practice 6,Argumentation
“The student can work with scientific explanations and theories.
Argumentation involves justifying, constructing explanations, making claims, and evaluating explanations. One place on the AP Physics Exam where this Science Practice is often assessed is the “Paragraph-Length Explanation” question. There is one of these on every AP Physics 1 and 2 exam. In the Paragraph Length Explanation question, students tie together several different ideas in physics to explain the behavior of a physical system. This is quite challenging!
Modeling students should be well-trained in these skills. The skilled modeling teacher is constantly demanding that their students justify and explain physics.
Science Practice 7,Making Connections
“The student is able to connect and relate knowledge across various scales, concepts, and representations in and across domains.“
Isn’t this the goal of all science teachers, but especially modeling science teachers? A great example of this is the placement of the projectile motion unit in the modeling workshop I attended. Instead of being in the first unit or two, projectile motion was placed in unit 6. This was so that students could use all of the tools they have been taught in the early units: graphical models, mathematical models, pictorial models motion maps (the infamous “dot diagrams” that bedevil so many students), free-body diagrams and the whole force concept. Instead of projectiles being a scary, painful assault of obscure equations, students see it in the context of the course. It becomes both easier to understand and less scary by this simple adjustment.
Here is an example (from the released 2018 AP Physics 1 Free-Response Questions) of how the AP exam assesses both Argumentation and Making Connections. In answering this question, students must put together two areas of physics: momentum and oscillation.
I hope this all makes sense. Please comment or ask questions if you feel the need.
Go to the AMTA website (modelinginstruction.org) and check out all of the resources for modeling, if you’re new to it. A modeling workshop is great background for teaching the Science Practices in AP Physics.
CASTLE stands for Capacitor-Aided System for Teaching and Learning Electricity.
It is a conceptual curriculum available for download from Pasco Scientific (go to https://www.pasco.com/prodCompare/castle-kit/index.cfm and scroll down to find the downloads). The curriculum is a basically complete set of activities, demonstrations, student classwork, homework, and quizzes.
A teacher guide is available by contacting me (or Pasco Scientific).
It takes a lot of time for students to complete the whole curriculum, but there are benefits. The curriculum is student-guided and inquiry-based, and emphasizes deep conceptual understanding (there are virtually no calculations and equations). Because of time constraints, my students, even my students in “on-level” physics where there is less time pressure, don’t do all of the activities. I am presenting some of the useful ideas here, so that you can see the benefit of the curriculum and perhaps make use of some of the ideas even though you don’t use the whole thing (which would be ideal, but won’t work for everyone).
Any of these activities that use a capacitor and bulbs to visualize what is happening in a circuit will not work with ordinary capacitors. As far as I know, Pasco.com is the only source for the capacitors that are utilized in the CASTLE curriculum. But, many of the activities below do not require the CASTLE capacitors.
1.2 Activity: “Using the compass to investigate a closed loop.”
A compass is placed under one of the wires in a circuit.
The deflection of the needle indicates something is happening in wires.
Reversing the battery reverses the deflection – whatever is happening has a direction.
Moving the compass to different parts of the circuit shows the same deflection – indicates that whatever is happening in the wires happens everywhere. Charge is everywhere in the circuit. The battery provides energy that makes charge move/causes charge to do work, but is not the source of charge (See also Activity 8.1).
1.11 Activity: “Lighting a bulb with a single cell”
Students are given a miniature bulb, a D cell and a single wire. They are challenged to light the bulb using only those materials. Students are given a “dissected” light bulb to examine.
An incandescent bulb must provide a single conducting path for charge to move through the bulb, including the filament
Charge must enter and leave through conducting parts of the bulb
Insulating parts of the bulb separate the conducting parts to provide the single path
2.3 Activity “Additional Symbols for Circuit Diagrams”
Try drawing “starbursts” to represent bulb brightness:
And drawing “Arrowtails” to represent current magnitude and directions:
2.6 Activity “Examining filaments under magnification” and 2.8 “Comparing the resistance of a bulb to a wire”
This is done after students observe that adding resistors or bulbs in series to a circuit decreases the brightness of a bulb. They examine the filaments of incandescent bulbs using magnifying lenses. The filament wires are much thinner than the support wires and connecting wires (alligator clip leads). Adding a long wire to a circuit does not appreciably change the brightness. Connecting a wire in parallel with a bulb causes the bulb to go out, as nearly all of the flow stays in the wire. Students deduce that most of the resistance is in the bulb.
Most of the resistance is in the bulb
The filament of the bulb is much thinner than other parts of the circuit
Thinness appears to equate with increased resistance
In a series circuit, a long bulb is brighter than a long bulb – since current is the same in the series circuit, the brightness of the bulb must depend on the resistance of each bulb. The filament of the round bulb must have less resistance than the filament of the long/the filament of the round bulb is thicker than the filament of the long bulb a thin filament has high resistance (see pictures below)
2.7 Activity “Detecting the resistance of straws to air flow”
In this activity different sized straws are used as an analogy for conductors in a circuit. Air is a compressible fluid that serves as the analogy for electric charge in the circuit. Coffee stirrer straws, ordinary drinking straws, bubble-tea straws, and paper towel tubes are all useful for this activity. Students blow through the straws and observe that resistance to airflow decreases with diameter. Putting like straws together with tape illustrates the series and parallel relationship with resistance.
Resistance to flow decreases with increased diameter
Resistance to flow increases with increased length
Resistance to flow decreases when “resistors” are arranged in parallel, increases when they are arranged in series.
2.8 Activity “Comparing the Resistance of Wire with a Filament”
Students insert a long wire into their circuit and observe that the compass needle deflects the same as before. Then they insert a second bulb in series into their circuit, and observe less deflection. This leads to the conclusion that wire has negligible resistance and bulbs have significant resistance.
4.2 Activity “Exploring air as an analogy”
Two linked hypodermic syringes (minus needles) show how pressure equalizes in a circuit. Potential difference (voltage) in a circuit acts like pressure differences in the syringes.
When circuit elements are connected to a source of electric pressure (a battery, for instance), the pressure quickly equalizes
Although the elements may be different, the pressure equalizes if it can.
4.7 Activity: How below-normal air pressure behaves (Air Capacitor)
In this activity, students work with an air capacitor (shown above in schematic and below in a photograph).
Blowing air in or out causes the balloon membrane to move, displacing air and/or changing the pressure within the capacitor. This is analogous to the flow of charge into and out of a capacitor. Air/Charge is already present in the capacitor, and is displaced from one side or the other, rather than moving through the capacitor. The balloon membrane acts like a dielectric, insulating one side from the other.
4.9 Commentary “Color Coding for Electric Pressures in a Circuit”
In this section, students use colored pencils to represent levels of electric potential in a circuit by color-coding schematics of the circuit. Once students understand what is expected, it is very quick to determine which bulbs in a circuit will be the brightest, or identify any bulbs that will not light (because both ends are at the same “electric pressure”). Try color-coding this circuit:
See below for a CASTLE-style representation of an RC circuit charging.
8.1 Activity “Circuit with a Conducting Island”
Build the circuit, predict what will happen, and connect it. The bulbs light and then go out. Charge that lights the bulbs must not have come from the battery, since the capacitor has insulators that don’t let charge through. Charge everywhere in the circuit moves until the electric pressures are all equalized. Energy is stored in the capacitors when they charge, but not a net charge.
There are twelve sections in CASTLE. The later sections delve into advanced topics, such as electric fields, semiconductors, magnetism and induction, and electromagnetic signal propagation and detection. All without making significant use of mathematics and equations. There are great teaching ideas in those sections, I just chose to highlight some sections that may be more broadly applicable.
You can download the curriculum from Pasco.com. Or leave me a message below /send me an email and I can share the entire curriculum, including a few things that are not available on the Pasco website.
Pasco Scientific is a convenient source of good-quality materials for the CASTLE kit used by students in the curriculum. You may be able to find everything in the kit cheaper elsewhere, but the capacitors. I have never seen those specific capacitors (High Capacitance, relatively high Voltage, and non-polar) anywhere else.