Reading Quiz

Question 1:

Consider a (planar) surface (like one face of a cube) in a uniform electric field.
Which of the following cases has the largest electric flux?
(1) The surface is parallel to the electric field or
(2) The surface is perpendicular to the electric field. Briefly explain.

Answer:

  1. The surface perpendicular to the electric field has the most flux through it because it has more surface area for the field to go through. A surface parallel to the field, in fact, has no surface area for the electric field to go through.
  2. 2, because electric flux is the product of the magnitude of the electric field, the surface area, and the cosine of the angle between the two. since the cosine of 90 degrees is zero, case one would have an electric flux of zero, while case two would have the maximum electric flux possible with that electric field and surface area.
  3. Flux is proportional to the number of field lines penetrating the gaussian surface. If the field is parallel, none of the lines pierce the surface.
  4. Case number 2. Electric flux is the surface area multiplied by the electric field, the larger the area the larger the flux will be.
  5. Perpendicular. Electric flux is determined by the amount of electric field lines penetrating the surface. A perpendicular surface captures the most field lines, so it has the highest possible flux for a given area.
  6. when the surface is parell to the field
  7. Electric flux is largest when the surface is perpendicular to the field. If it is parallel to the field then there is no flux because no field lines run perpendicular to it.
  8. The electric flux would be greater for the surface perpendicular to the field, because only the component of the field that is normal to the surface produce a flux.
  9. When the surface is perpendicular there is the most electric flux because the closer to perpendicular the plane gets, the more field lines that pass through the plane. Whereas when the surface is parralel, almost no field lines pass through it.
  10. When the surface is perpendicular to the electric field. This is because electric flux is the number of field lines penetrating the surface. The most lines are going to go through the surface when it is perpendicular.
  11. Perpendicular b/c then the angle b/t E and the serfaces normal would be 0 and then COS0=1 so the electric flux will be greatest.

Question 2:

What's a descriptive (non-mathematical) statement of Gauss's Law?

Answer:

  1. The number of field lines going out of any surface that encloses charge is proportional to the net charge enclosed by that surface.
  2. The net outward electric flux thru any closed surface is proportional to the net charge inside the surface. In other words, the net flux coming out of the closed surface depends on the charges inside the surface.
  3. The number of lines coming out of a surface enclosing charge is propotional to the charges in the surface.
  4. Gauss's Law is a measure of the number of field lines that penetrate any surface, the term for this is electric flux.
  5. The relation between the electric flux flowing out a closed surface and the electric charge enclosed in the surface.
  6. The net outward flux passing through a closed surface is proportional to the internal charge of the suface
  7. Gauss's law state's that the sun of the field lines out of a closed surface is equal to the net charge within the closed surface.
  8. The net lines out of the closed surface is proportional to the net charge withing the surface.
  9. The net outward flux through an closed surface equals 4(pi)k times the net charge inside the surface.
  10. Gauss's Law states that the number of field lines out of a surface is proportional to the charge that the surface encloses.
  11. if you add up all of the components of the charge(feild lines) leaving the object it is equal to the amount of charge contained in the object.

Question 3:

Sometimes it's extremely convenient to use Gauss's Law to calculate electric fields.
Sometimes it's a disaster. When is it convenient to use Gauss's Law to calculate electric fields?

Answer:

  1. Gauss's law is convenient when dealing with an electric field from a symmetrical charge distribution. If the charge distribution is an irregular shape, the surface integral is very difficult and makes the problem very hard.
  2. For symmetric surfaces- planes, spheres, cylinders, etc.
  3. When the charge distribution is symmetrical
  4. It is convenient to use Gauss's Law when calculating the electric fields from symmetric objects.
  5. For charge distributions that are very symmetric.
  6. When it is surface/shape
  7. It is convenient to use Gauss's law with things that have even charge distribution like cylinders and sphere's and disks of charge.
  8. If the charges are symmetric.
  9. When it is a highly symmetrical charge distribution.
  10. It is useful when the charge distributions are symmetric. It is also useful when the conductor is in electrostatic equilibrium.
  11. when the electric feild varies inversly with the 1/R^2. you can't use Gauss's law when you are near the end of a finite line charge or when the E is not Perpendicular to the surface.

Question 4:

What concept(s) or application(s) from the reading did you find interesting or intriguing?
Anything you'd like to discuss further?

Answer:

  1. Figure 22-23 is very interesting. I don't totally understand why the electric field has such an effect on the candle's flame. I would kind of like to try this (or at least play with a Van de Graaff apparatus!).
  2. Not really
  3. I found the mathematical definition of gauss's law interesting.
  4. All of the topics are interesting, however I am having trouble with some of the fundamentals.
  5. Maybe a bit about the differential form of Gauss' Law.
  6. The feild lines and how a drawing can measure them.
  7. Does an infinite line of charge ever come up in nature. What I mean is, is it reasonable that we are doing problems with infinite lines of charges, because would we ever encounter them in real life.
  9. Well I have already seen a reasonable amount of this in my high school class, but nonetheless, I still love all of it. However nothing in particular is more fascinating than something else.
  10. Nothing specific.
  11. could you explain the reasons for gauss's law in more depth

Question 5:

What (if any) were the conceptual or mathematical difficulties that you had with this reading?
What do we need to spend class time on?

Answer:

  1. When I learned this last year, I always had trouble understanding how the "soup can" gaussian surface worked... I'm still having trouble with the concept especially now that I'm a little rusty. The spherical surface is pretty straight forward though.
  2. Some of the vector analysis stuff was overwhelming, but the book derived easier equations
  4. The Calculus is fairly difficult to understand, especially some of the derivations.
  5. Does the procedure to calculate E-fields (hand out from Wed) apply to Gauss' Law?
  6. not really it was pretty self explantory
  7. This stuff doesn't seem too bad. Could we play with a Vandergraff generator in our class because that would be really cool?
  8. How to use Gauss's law to calculate the electric field.
  9. Most of it is more reviewish material. I just need to refresh my memory on some of this stuff, but other than that, I think I'm ok with most of it.
  10. Once again, nothing specific although I would love to go over all of it in class.