# Electrostatics & DC Circuits Learning Goals Fa13

I really fell behind on blogging this semester. One thing I wanted to do on the blog was keep a record of my learning goals for each unit as this was the first semester I really made use of unit-scale learning goals. With the semester wrapped up, let me record the learning goals I used this semester before I start revising them for next semester.

For electrostatics and DC circuits…

**Content Learning Goals**

1. Draw conclusions about whether objects are positively charged, negatively charged, or neutral based on their interactions with other objects. Student can also describe and sketch what happens to charges inside a neutral object when a charged object is brought nearby while the neutral object is either grounded or not grounded.

2. Briefly describe in words the meaning of: conductor, insulator, electric field, electric potential, electric potential energy.

3. Use Coulomb’s Law to calculate the magnitude and direction of the force between point charges. The student can also use vector addition to determine the net force.

4. Use E = kq/r^{2} to calculate the electric field due to a point charge and use integration to determine the electric field due to a finite length line charge and a charged ring.

5. Use F = qE to determine the force and resulting motion of a charge placed in an external electric field.

6. Sketch and describe in words the electric field due to a point charge, an electric dipole, a line charge, a ring charge, and a charged sphere. Student can also sketch the approximate electric field due to irregularly shaped conductors. Student can draw conclusions about the relative strength of the electric field at different locations based on a sketch of electric field lines.

7. Sketch electric field lines (including direction) when given labeled equipotential lines or vice versa. Student can relate equations for the electric field and the electric potential using one equation to determine the other.

8. Use V = kq/r to calculate the electric potential due to a point charge and use integration to determine the electric potential due to a finite length line charge or charged ring.

9. Use potential energy and work equations to construct conservation of energy expressions. Student can use these expressions to determine the speed of a charge, the potential energy of a configuration of charges, or the work required to construct a given charge configuration.

10. Use Gauss’s Law to calculate the electric field, charge, or charge density in problems with planar, cylindrical, or spherical symmetry. Student can also explain why symmetry is necessary in order for Gauss’s Law to be useful in a given problem.

11. Describe and justify the four defining characteristics of conductors in equilibrium.

12. Explain in words what current, voltage, and resistance mean in terms of electric charges. Student can also use Ohm’s Law to relate these quantities.

13. Identify and draw series and parallel connections on circuit diagrams. Student can also use physical arguments about conservation of charge and conservation of energy to explain why current is the same through elements in series and voltage drops are the same across elements in parallel.

14. Build a physical circuit (consisting of batteries, resistors, and light bulbs) based on a circuit diagram and measure current or voltage drops anywhere in the circuit.

15. Explain why power = current*voltage drop, use Ohm’s Law to write power in other useful ways, and use power to draw conclusions about the brightness of light bulbs.

16. Add resistors in series and parallel and use the concept of equivalent resistance to determine the current at any point in a circuit with multiple resistors and multiple branches.

17. Use Kirchoff’s voltage and current laws to write a system of equations for a circuit with multiple loops and one or more batteries. Student can solve the system of equations to determine current (value and direction) anywhere in the circuit.

General Skills Related to this Unit

1. Developing models to help us interpret equations, make predictions, reason conceptually, and hone our intuition.

2. Using integrals to add together many tiny pieces and building a conceptual understanding of what it means to integrate something.

3. Using symmetry to simplify problems and make predictions about the form of a solution.

**Experiential Value of this Unit**

1. Like our unit on thermodynamics, this unit involves making the invisible visible. Much of our understanding of charged objects and of electrical circuits is based on picturing the position or motion of physical charges. This will allow you to visualize what is happening inside things that were previously sealed off from your view.

2. Our discussions of voltage differences and electric fields will unify batteries, power lines, electric shocks, and lightning in ways you may not have previously seen. Seeing these objects and phenomena in terms of voltage differences will draw your attention to the importance of the “ground” or “negative” side. What you previously saw as a single object with “high voltage” you will now see as simply one side of a two sided voltage difference.

3. You will notice that the terms voltage, power, and energy are constantly being used incorrectly in movies, television, and advertisements (even on battery packages themselves). This will be very annoying.

4. Our vision of current flow will be one of collective motion where each charge is influencing its neighboring charges. You will start to see other phenomena such as air or water flow, crowds moving through a hallway, birds or fish traveling as flock or school in similar terms. You may find yourself applying our conceptual explanation of how current divides when it reaches a junction to analogous behaviors in all of these other systems.