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activities:guides:vfvring 2011/12/08 16:24 activities:guides:vfvring 2019/06/03 13:18 current
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  * The final component is that students need to recognize an elliptic integral and what to do when they run into one. Most commonly students have never seen such `unsolvable' integrals in their calculus classes. In our case we had students do the power series expansion before the integral (see below).   * The final component is that students need to recognize an elliptic integral and what to do when they run into one. Most commonly students have never seen such `unsolvable' integrals in their calculus classes. In our case we had students do the power series expansion before the integral (see below).
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  * With the charged ring in the $x,y-$plane, students will make the power series expansion for either near or far from the plane on the $z$ axis or near or far from the $z$ axis in the $x,y-$plane. Once all students have made significant progress toward finding the integral from part I, and some students have successfully determined it, then the instructor can quickly have a whole class discussion emphasizing some of the points above, followed by telling students to now create a power series expansion. The instructor may choose to have the whole class do one particular case or have different groups do different cases.   * With the charged ring in the $x,y-$plane, students will make the power series expansion for either near or far from the plane on the $z$ axis or near or far from the $z$ axis in the $x,y-$plane. Once all students have made significant progress toward finding the integral from part I, and some students have successfully determined it, then the instructor can quickly have a whole class discussion emphasizing some of the points above, followed by telling students to now create a power series expansion. The instructor may choose to have the whole class do one particular case or have different groups do different cases.
-  * If you are doing this activity without having had students first create power series expansions for the electrostatic potential due to two charges, students will probably find this portion of the activity very challenging. If they have already done the <html><a href="http://www.physics.oregonstate.edu/portfolioswiki/doku.php?id=activities:main&file=vfvpoints">Electrostatic potential due to two points</a></html> activity, or similar activity, students will probably be successful with the $y$ axis case without a lot of assistance because it is very similar to the $y$ axis case for the two $+Q$ point charges. However, the $y$ axis presents a new challenges because the ``something small'' is two terms. It will probably not be obvious for students to let $\epsilon = {2R\over r}\cos\phi' + {R^2 \over r^2}$ (see Eq. 17 in the solutions) and suggestions should be given to avoid having them stuck for a long period of time. Once this has been done, students may also have trouble combining terms of the same order. For example the $\epsilon^2$ term results in a third and forth order term in the expansion and students may not realize that to get a valid third order expansion they need to calculate the $\epsilon^3$ term.+  * If you are doing this activity without having had students first create power series expansions for the electrostatic potential due to two charges, students will probably find this portion of the activity very challenging. If they have already done the <html><a href="http://www.physics.oregonstate.edu/portfolioswiki/doku.php?id=activities:main&file=vfvpoints">Electrostatic potential due to two points</a></html> activity, or similar activity, students will probably be successful with the $z$ axis case without a lot of assistance because it is very similar to the $y$ axis case for the two $+Q$ point charges. However, the $y$ axis presents a new challenges because the ``something small'' is two terms. It will probably not be obvious for students to let $\epsilon = {2R\over r}\cos\phi' + {R^2 \over r^2}$ (see Eq. 17 in the solutions) and suggestions should be given to avoid having them stuck for a long period of time. Once this has been done, students may also have trouble combining terms of the same order. For example the $\epsilon^2$ term results in a third and forth order term in the expansion and students may not realize that to get a valid third order expansion they need to calculate the $\epsilon^3$ term. 
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==== Activity: Wrap-up ==== ==== Activity: Wrap-up ====
-  * Discuss which variables are variable and which variables are held constant - Students frequently think of anything represented by a letter as a `variable' and do not realize that for each particular situation certain variables remain constant during integration. For example students frequently do not see that the $R$ representing the radius of the ring is held constant during the integration over all space while the r representing the distance to the origin is varying. Understanding this is something trained physicists do naturally while students frequently don't even consider it. This is an important discussion that helps students understand this particular ring problem and also lays the groundwork for better understanding of integration in a variety of contexts. For more information on this topic, see [[whitepapers:variables:start|Students understanding of variables and constants]].+  * Discuss which quantities are variable and which variables are held constant - Students frequently think of anything represented by a letter as a `variable' and do not realize that for each particular situation certain quantities remain constant during integration. For example students frequently do not see that the $R$ representing the radius of the ring is held constant during the integration over all space while the r representing the distance to the origin is varying. Understanding this is something trained physicists do naturally while students frequently don't even consider it. This is an important discussion that helps students understand this particular ring problem and also lays the groundwork for better understanding of integration in a variety of contexts. For more information on this topic, see [[whitepapers:variables:start|Students understanding of variables and constants]]
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 +  * Emphasize that while one may not be able to perform a particular integral, the power series expansion of that integrand can be integrated **term by term**.
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  * Maple/Mathematica representation of elliptic integral - After finding the elliptic integral and doing the power series expansion, students can see what electric potential `looks like' over all space by using a {{activities:guides:vfvring.mw|Maple}} or {{activities:guides:vfvring.nb|Mathematica}} worksheet.   * Maple/Mathematica representation of elliptic integral - After finding the elliptic integral and doing the power series expansion, students can see what electric potential `looks like' over all space by using a {{activities:guides:vfvring.mw|Maple}} or {{activities:guides:vfvring.nb|Mathematica}} worksheet.
-This activity is a part of the [[whitepapers:sequences:emsequence:start|Ring Sequence]], which uses a sequence of activities with similar geometries to help students learn how to solve a hard activity by breaking it up into several steps ({{.:len_s_master_s_project.pdf|A Master's Thesis}} about the Ring Sequence). The other activities in the sequence are:+This activity is a part of the [[whitepapers:sequences:emsequence:start|Ring Sequence]], which uses a sequence of activities with similar geometries to help students learn how to solve a hard activity by breaking it up into several steps ([[publications:start#student_theses|A Master's Thesis]] about the Ring Sequence). The other activities in the sequence are:
-  *Prerequisite Activity: +  *Preceding Activity: 
-    * [[courses:activities:vfact:vfvpoints|Electrostatic potential due to two point charges]]+    *[[courses:activities:vfact:vfvpoints|Electrostatic Potential Due to Two Point Charges]]: Students use what they learned about finding the distance between two points and apply what they know about power series approximations to find a general expression and asymptotic solution to the electrostatic potential due to two point charges.
  *Follow-up Activities:   *Follow-up Activities:
-    * [[courses:activities:vfact:vfering|Electric field due to a ring of charge]] +    *[[courses:activities:vfact:vfering|Electric Field Due to a Ring of Charge]]: In this small group activity, students use the definition of the electric field as $\vec{E}(\vec{r})=\frac{1}{4\pi\epsilon_0}\int_{ring}{\frac{\lambda(\vec{r'})(\vec{r}-\vec{r'})|d\vec{r'}|}{|\vec{r}-\vec{r'}|^3}} $ in order to work out the electric field due to a ring of charge. 
-    * [[courses:activities:vfact:vfaring|Magnetic vector potential due to a spinning ring of charge]] +    *[[courses:activities:vfact:vfaring|Magnetic Vector Potential Due to a Spinning Ring of Charge]]: This small group activity is the magnetic analogy to [[courses:activities:vfact:vfvring|Electrostatic Potential Due to a Ring of Charge]] where students solve for the magnetic vector potential due to a spinning ring of charge. The set up for this problem is more complex because students now must think about current densities and the inherent vector nature of the magnetic vector potential. 
-    * <html><a href="http://www.physics.oregonstate.edu/portfolioswiki/doku.php?id=activities:main&file=vfbring">Magnetic field due to a spinning ring of charge</a></html>+    *[[courses:activities:vfact:vfbring|Magnetic Field Due to a Spinning Ring of Charge]]: Building from their experience with the previous exercises, students  in this small group activity use techniques from the previous activities to obtain an expression for the magnetic field due to a spinning ring of charge.  
 + 
 +This activity is part of the sequence of activities addressing [[whitepapers:sequences:scalarfieldseq|Representations of Scalar Fields]] in the context of electrostatic potentials. 
 + 
 +  *Preceding Activities: 
 +    *[[swbq:emsw:vfswpointpot|Electrostatic Potential due to a Point Charge]]: This small whiteboard question asks students to recall the electrostatic potential due to a point charge which results in discussions likely to include notation of the distance from the origin to a point charge.  
 +    *[[courses:activities:vfact:vfdrawquadrupole|Drawing Equipotential Surfaces]]: This small group activity has students construct a contour plot of the electrostatic potential, level curves of equipotential, in the plane of four point charges. 
 +    *[[courses:activities:vfact:vfvisv|Visualizing Electrostatic Potentials]]: Students begin by brainstorming ways in which to represent three-dimensional scalar fields in two-dimensions and then use a Mathematica notebook to explore various representations for a distribution of point charges.

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