Charged Object Moving in a Capacitor
Lab 4 Review textbook Chapter 16 which involves the vector characteristics of a moving charged object within a charged parallel plate capacitor.
• This simulation can be downloaded from within your course under “PH221.Simulations”; its file name is “#15 Charge and Cap.ip”.
A positively charged particle is moving horizontally when it enters the region between the plates of a capacitor as the simulation illustrates. (a) Draw (sketch) the
trajectory that the particle follows in moving through the capacitor. (b) When the particle is within the capacitor, which of the following four vectors, if any are
parallel (||) to the electric field E inside the capacitor: the particle’s displacement (), its velocity (v), its linear momentum (p), and its acceleration (a)? For
each vector, explain why the vector is or is not parallel to the electric field of the capacitor.
Run the simulation noting the particle’s trajectory (as indicated by the “tracking” or “strobes”) while inside the capacitor cavity. Also note the velocity and
acceleration vector, v and A, respectively arrows. Fill in the answers for the blanks in the Lab Answer Sheet at the end of this lab.
A capacitor is a charge storage device. A parallel plate capacitor consists of parallel conducting plates separated by an insulator. In this experiment, the insulator
is air and there is equal but opposite charges (+Q and –Q) placed on each conducting plate (See Figure 18.25, Section 18.6 and 18.7 in your textbook). This virtual lab
investigates the effects (if any) of a positively charged particle midway between the oppositely charged plates of a parallel plate capacitor moving in a + x-
direction. Just as in Lab 3, there will exist an electrostatic (Coulomb) force on the charged particle when it is inside the capacitor.
In this lab, you will investigate electric field (E) lines. Electric charges create an electric field in space surrounding them. Electric field lines essentially give
us a “map” of the direction and strength (magnitude) of the E field at various places in space. E lines are always directed away from positive charges and toward
negative charges (see Figure 18.23, textbook Section 18.7, and Lesson 3). In Figure 18.27 the absence of E lines indicates that the electric field is relatively weak
between the two positive charges. Since you will be performing in this experiment a virtual mapping of E lines for a certain charge distribution, carefully study
Conceptual Example 13 (“Drawing Electric Field Lines”) for the dos and don’ts of mapping E field lines.
Electric Field Lines Mapping Rules
-The E lines do not cross each other
-The closer the lines are together, the stronger the E in that region
-The field lines indicate the direction of E; the field points in the direction tangent to the field line at any point
-The lines are drawn so that the magnitude of the electric field, |E|, is proportional to the number of lines crossing unit area perpendicular to the lines. The closer
the lines, the stronger the field
-E lines start on + charges and end on – charges; the number starting or ending is proportional to the magnitude of the charge.
