Reading Quiz

Question 1:

What continous charge distribution(s) have an electric field that falls off inversely
(not inversely squared) with distance? Describe any special conditions that apply
(e.g. in plane or along axis, etc.)

Answer:

  1. An infinitely long wire produces an electric field that decreases inversely with distance rather than inversely squared with distance.
  2. An infinite line charge defined by E=2k(lamda)/R.
  3. E due to a continuous charge distribution along a line sement, or along an infinite line (at a point off the line).
  4. If there is an infinite line charge or along the axis of a disc charge.
  5. Electric field falls off inversely at a distance R from an infinite line of charge. If you are on the axis however, the electric field is infinite along the axis.
  6. Infinite line charges, like along a line or axis.
  7. A continuous charge distribution along a line of charge. Charge must be behind or in front of the line of charge, cannot be directly over it.
  8. An infinite line charge with uniform charge distribution.
  9. An infitite line charge falls inversly off with distance. It is special cause it is a uniformly charged infite line.

Question 2:

How can you obtain a uniform electric field?

Answer:

  1. You can get a uniform electric field from an infinite plane of continuous charge. This can be calculated by finding the charge on the axis of a disk and letting the radius of the disk go to infinity.
  2. In an infinite plane charge defined by E=2(pi)k(sigma).
  3. a plane of charge
  4. If you have an infinate plane of charge.
  5. You can obtain a uniform eletric field all around a sphere of uniform charge distribution in radiating spherical shells outward. The field due to an infinite plane of charge is uniform.
  6. Look over very small intervals/areas/spaces
  7. You can obtain a uniform electric field by using an infinite plane of charge; the field strength does not depend on x.
  8. The area between two infinite line charges.
  9. an arbarialy formed conductor carrying a chartge on its surface

Question 3:

Under what (physical) conditions will the electric field inside a conductor be zero?

Answer:

  1. If any conductor is in electrostatic equilibrium (the charge is allowed to redistribute without limitation), the field inside it will always be zero.
  2. The conductor has to be in equilibrium, i.e. not accelerating.
  3. no external energy added
  4. If it is in electrostatic equilibrium.
  5. The electric field inside a conductor will be zero if there is a uniform charge density on the surface.
  6. There's no source of energy maintaining a current thru the conductor and the free charge redistributes itself. This creates an electric field which cancels out the external field inside the conductor.
  7. There is no source of energy to maintain an electric field inside the conductor.
  8. If all the charges within the conductor are distributed evenly, the net charge is zero and there are no other charges nearby.
  9. the field inside a conductor is always zero as long as the conductor was neutral before the charge was introduced

Question 4:

When the electric field inside a conductor is zero, what two things do you know about the
electric field just outside the conductor's surface?

Answer:

  1. If the field inside a conductor is zero, the field just outside the surface is the same as if the total charge on the object was all concentrated at the conductor's center. We also know that the field just outside the conductor has a magnitude equal to the surface charge density divided by the permittivity of free space constant.
  2. 1. The field is perpedicular to the surface. 2. The field is given by E=(sigma)/(fancy e-thing naught).
  3. its magnitude is equal to the surface charge density divided by the permittivity of space, and it's direction is perpendicular to the surface.
  4. It is equal to the surface charge density over the permittivity of free space. This is twice the field produced by a uniform disk of charge.
  5. If the electric field inside a condutor is zero then you know that there exists an electric field just outside the conductors surface and that it drops by a factor of 1/(r^2) as you move away from the surface.
  6. it's perpendicular to the surface and is equal to the surface charge density divided by the permittivity of free space constant.
  7. It is equal to sigma/permittivity of free space.
  8. It is also zero.
  9. that the distribution is uniform on the outer surface of the conductor regarless of the internal location of the charge

Question 5:

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

Answer:

  1. I would like to know how a charge could be inside a charged conductor. If the point charge inside is the same as the charge on the surface, is there no field anywhere outside the system?
  2. N/A
  3. In one of my years of high school physics, there was a problem in which a conductor was inserted into an electric field. The answer to the problem depended on the fact that the field inside the conductor, and therefore the potential change from one end to the other, was zero, but we never learned why this was true. I don't know if I would have found this fact so profoundly fascinating if it had not been for that problem, but it seems really cool.
  4. I wouldn't mind talking more about the discontinuity of En (22-4).
  5. I thought that the calculus of it was very interesting. I found the mathematical explanations clarified things a lot.
  6. Everything in the first section
  7. Discuss Gauss's Law
  8. The way electric fields are affected by the shape and charge distridution of the object.
  9. Not really

Question 6:

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. I've done pretty much all of this in my AP physics class last year but some of it may be shaky now. It would be helpful if we did examples of calculating the field from a disk as well as gaussian surface problem on the board. I just learn things best by doing them or seeing them for myself.
  2. I didn't learn any of this in high school, so could you maybe quickly go over everything so I know that I'm doing the problems the right way?
  3. Nope. Looks good.
  4. I don't think I had any specific trouble but most of this is relatively new to me so I wouldn't mind going over any of it in class. We did some of this before but not too much.
  5. There is a lot of material in this one reading, and while I understand most of each thing, I don't fully understand the concepts demonstrated in the reading. If you could show us a few real life examples of these concepts in the form of worked out problems on the board that would be really helpful. I just don't really get the proper method of solving these problems.
  6. Going over some of these derivations would be nice
  8. The integration methods.
  9. The conductor part as a whole was confusing to me.