### Notes:

The Electric Field Intensity Concept Builder is an adjustable-size file that displays nicely on smart phones, on tablets such as the iPad, on Chromebooks, and on laptops and desktops. The size of the Concept Builder can be scaled to fit the device that it is displayed on. The compatibility with smart phones, iPads, other tablets, and Chromebooks make it a perfect tool for use in a 1:1 classroom.

### Teaching Ideas and Suggestions:

Electric Fields are a common topic in first-year Physics courses. The topic is both conceptual and mathematical. The mathematics is rather straight-forward from an operational standpoint. Most difficulties are conceptual in nature. Students with poor conceptual understanding have difficulty with exactly what operations must be performed to do the mathematics. This Concept Builder seeks to fill the gap between the conceptual and the mathematical aspects of electric fields.

Questions in this Concept Builder come in the form of an 8-row table with 1-2 blank cells per row. Students must determine the numerical value of the blanks. To be successful, students must know:
• The Source Charge (call it Q, "big Q") is the charged object that creates the electric field.
• The Test Charge (call it q, "little q") is a charged object that can be used to test the strength of the source's electric field. The test charge is placed in the space surrounding the Source Charge and experiences an electric force.
• The strength of the electric field can be computed from the amount of force experienced by a test charge and the amount of charge on the test charge. The electric field intensity (E) is the force per charge - F/q.
• Electric field intensity (E) depends on (translate as "is affected by") two variables - the amount of charge on the source charge (Q) and the distance (d) from the source charge. The quantity E is directly proportional to the quantity Q and inversely proportional to the square of the disance d. Doubling Q will serve to double the E, provided that the distance is not changed. Doubling d will cause E to become one-fourth the strength, provided that Q is not changed.
• Changes in the charge on the test charge (q) will affect the force but not affect the electric field strength. The strength of the electric field is independent of the amount of charge on the test charge.
These bullet points are the main concepts that must be internalized by students in order to be successful with this Concept Builder.

The Concept Builder avoids mere plug-and-chug problem-solving and emphasizes relationships. It does this in two ways. First, there are no numerical values given for d. Without a distance, plug-and-chugging into an equation like E = k•Q/d2 is impossible. When there is a change in d, it's always a doubling of distance, thus requiring students to use the inverse-square relationship in a conceptual manner. Second, the given values are such that students could complete the table without hardly ever using a calculator or plugging into an equation. In proceeding from one row to the next row, a change is typically made in one independent variable. The change is usually a doubling or a halving of the value, thus inviting a student to think proportionally. That is, a student can more quickly arrive at an answer by knowing that ta doubling of a test charge doubles the force but has no affect upon the electric field intensity. Knowing and using this principle is a time-saver and allows the user to avoid having to use a plug-and-chug approach.

Teachers (and students) might wonder about the formula for calculating the Health Percent. After completion of the first problem, the formula removes 4% from 100% for every missed answer. And answer is considered missed answer if it is present in a grey-background cell when the Check Answers button is tapped and ends up being an incorrect answer. Blank cells do not count as missed answers. Students with a Health Percent of 60 or higher are considered to have completed the activity after the first problem/table. Those with less than 60% are presented with a second problem.

This Concept Builder is intended for use near the middle stages of a learning cycle on electric fields. Teachers using the Concept Builder with their classes should preview the activity (or view the Questions in the separate file) in order to judge the appropriateness of it for their classes. It is highly recommended that students have some degree of comfort with the bullet points presented above before attempting this Concept Builder

We believe that the most valuable (and most overlooked) aspect of this concept-building activity (and any of our Concept Builders) is the Help Me! feature. This Help feature transforms the activity from a question-answering activity into a concept-building activity. The student who takes the time to use the Help pages can be transformed from a guesser to a learner and from an unsure student to a confident student. The "meat and potatoes" of the Help pages are in the sections titled "How to Think About This Situation:" Students need to be encouraged by teachers to use the Help Me! button and to read this section of the page. A student that takes time to reflect upon how they are answering the question and how an expert would think about the situation can transform their naivete into expertise.

### Related Resources

There are numerous resources at The Physics Classroom website that serve as very complementary supports for this Electric Field Intensity Concept Builder. These include:
• Minds On Physics Internet Modules:
The Minds On Physics Internet Modules include a collection of interactive questioning modules that help learners assess their understanding of physics concepts and solidify those understandings by answering questions that require higher-order thinking. Assignments SE8, SE10, and SE11 of the Static Electricity module provide great complements to this Concept Builder. They are best used in the middle to later stages of the learning cycle. Visit the Minds On Physics Internet Modules.

Users may find that the App version of Minds On Physics works best on their devices. The App Version can be found at the Minds On Physics the App section of our website. The aforementioned assignments can be found on App #4 of the six-part app series. Visit Minds On Physics the App.

• Physics Interactives: Our Physics Interactives section includes a collection of interactive simulations that help students visualize concepts by interacting and observing the relationships between variables. There are three simulations in the Static Electricity section of the Physics Interactives that will coordinate with this Concept Builder. The links are provided below. The Coulomb's Law interactives serves as a suitable pre-cursor to this Concept Builder. The Electric Field Lines and Electric Field Hockey activities are good follow-ups for those courses that emphasize the mathematics of projectiles and its use in solving problems. These include the following:

Coulomb's Law

Electric Field Lines

Electric Field Hockey

• Curriculum/Practice: Several Concept Development worksheets at the Curriculum Corner will be very useful in assisting students in cultivating their understanding, most notably ...

Electric Field

Electric Field Lines

Visit the Curriculum Corner - Electrostatics.

Additional resources and ideas for incorporating Electric Field Intensity into an instructional unit on Static Electricity can be found at the Teacher Toolkits section of The Physics Classroom website.  Visit Teacher Toolkits.