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Student Responses to Reading Quiz #2, due Monday January 26 Question 1: What continuous charge distribution(s) have an electric field that falls off inversely with distance? 1. lines and disks 2. A finite uniform line charge has an electric field that is inversely related to the distance squared, when the sample point is far from the charge. If the line charge is infinite, the electric field is inversely related to the distance 3. 4. The electric Field of a line charge when the line is very long or when we are very near the line charge drops off inversely with distance. 5. Finite Line Charges 6. The electric field due to an infinite line charge. 7. Infinite Line Charge 8. the electric field produced by an infinite line charge falls off inversely with distance. 9. An infinite plane, a disk, a ring, and lines with continuous charge distributions have an electric field that falls off inversely with distance. 10. infinite line charges 11. An electric field due to an infinite line charge falls off inversely because its magnitude decreases as 1/y. 12. All but the infinite plane of charge? I'm not sure. At least the infinite line charge does. 13. The continous charge distributions that have electrical fields that fall off inversely are the infinite and finite lines. 14. A line charge that is either extremely long or viewed from very close. 15. An infinite line charge has an E-field that falls off inversely with distance. (In a proportion of 1 to 1/x) 16. Line, ring, disk, spherical shell, solid sphere. 17. In situations where y << L, the test charge is very close to a line charge or when the line charge is very long. 18. Those that are sherical or pointlike have ekectric fields that fall off inversely with the distance 19. The electric field due to an infinite line charge has an electric field that falls off inversely with distance. (The y component of the electric field equals 2k*linear density divided by distance y). Question 2: How can you obtain a uniform electric field? 1. by placing a point charge inside a spherically symmetric condutor. 2. When the sample point is very far away, the electric field is uniform. 3. 4. A uniform electric field is created when the area of a uniform disk approaches infinity of we get very close to its surface. 5. Have a constant energy source (not quite sure). 6. If you set up two parallel infinite planes of charge the area confined between the planes will have a uniform electric field. 7. When sufficiently close to a uniformly charged disk, the disk can be approximated as an infinite plane of charge, in which case the electric field is uniform. 8. a uniform electric field is achieved when a conductor is in electrostatic equilibrium, which occurs almost the instant a metal is charged 9. An uniform electric field can be obtained through an infinite plane of charge. 10. infinite plane charges 11. It can be obtained through an infinite plane of charge because in this distribution, the field does not depend on x. 12. Since an infinite plane of charge puts off a uniform electric field, even when you can't generate an infinite plane of charge, you can approximate a uniform electric field up close enough to a large enough disk. If you can come up with some sort of "infinite" plane of charge that'll do it. 13. You can obtain a uniform electric field by have constant energy, which will create a constant force, which leads to a uniform electric field. (or you have a uniform electric field maker) 14. A uniform electric field is obtained with an infinite plane of charge; that is, a uniformly-charged surface that is either extremely large or viewed from a very short distance away. 15. Between two oppositely charged plates of equal magnitude, the electric field is uniform. 16. It is formed between two oppositely charged planes that are large compared to the distance between. 17. By putting a charge within or on a spherical conductor. 18. You can obtain a uniform electric field by being a a large distance away from a source charge 19. A uniform electric field can be obtained using a uniform charge distribution. Normally at distances far away from charge distributions, the electric field will be uniform. Question 3: Under what (physical) conditions will the electric field inside a conductor be zero? 1. When there is no charge inside the conductor. A hollow copper sphere can be positively or negatively charged or unetral and as long as there are no charges within the sphere there will be no electric field inside of it. 2. If the conductor is in electrostatic equilibrium, there is no net field inside the conductor. 3. 4. There will not be an electric field unless there is a source of energy to maintain a current through the conductor. 5. At electrostatic equilibrium, when there is no energy to maintain a current. 6. In electrostatic equilibrium the electric field inside a conductor must be zero. Since any net charge resides on the surface, if the conductor is in equilibrium the net flux through the surface must be zero. Then by Gauss's Law the electric field inside the conductor will be zero. 7. If the conductor has a net charge and there is no source of energy providing constant current, the free charge will redistribute itself on the surface such that the conductor reaches electrostatic equilibrium. At this point, the electric field inside the conductor is zero. 8. when a conductor is in electrostatic equilibrium, the electric field inside a conductor must be zero. 9. The electric field inside a conductor will be zero if the condutcor is in electrostatic equilibrium. When the conductor is in equilibrium, the electric filed will be perpendicular to the surface of the conductor. 10. in equilibrium 11. When there is no source of energy to maintain an electric current and therefore the free charge in the conductor redistributes itself to create an electre field that cancels the external field within the conductor. This is known as electrostatic equilibrium 12. When the conductor is in electrostatic equilibrium, the electric field enclosed will be zero. This is when all of the electric charge, assuming it is free to move and there's no external energy preventing it from reaching equilibrium, redistributes itself in such a way that a field is created within the conductor that cancels out all external fields inside the conductor. 13. A electric field inside a conductor will be zero, when the field outside of the conductor is zero. 14. There is no current or source of energy acting on the conductor, and the conductor has reached equilibrium. 15. If the net charge in a conductor is zero, then the electric field is also zero. 16. In electrostatic equilibrium 17. If there is no net force creating a current inside the conductor the charge will distribute itself so there is no electric field within the conductor. By using Gauss's Law we can prove that that means the all the charge will reside on the surface of the conductor. 18. When the conductor encloses a gaussian surface, the net electric field inside is zero (assuming that there are no charges inside the surface). 19. In electrostatic equilibrium, the electric field inside a conductor is zero. This means there's no source of energy to maintain a current within the conductor. The free charge will redistribute itsself so that it cancels out the external electric field within the conductor . Question 4: What (if any) are the conceptual and mathematical issues you are having difficulty with from the reading? 1. There are a lot of equations that look kind of confusing now just having read the sections but i see how they work and will probably be fine with them once we begin to use them. 2. Can we go over the idea about electric field near a uniform plane. 3. 4. I did not understand the explanation in 23-5 on why there is no electric field in a conductor. 5. All of it for the most part. I think that I'll be able to pick it up more after seeing examples and listening in class than by reading the section. 6. The geometry was a little hard to understand in the pictures when you had to set up an integral in order to calculate the electric field. I would like to see the steps in class. 7. None 8. 9. 10. none 11. I understand the concepts behind calculating an electric field from Coulomb's Law, I'm just a little confused on all the math involved. 12. The first question on this quiz. I don't know, I got confused for some reason. I think I'm just being stupid. 13. 23-5 is a bit confusing 14. None 15. none 16. Charge and field at conductor surfaces About math, I sent you couple of emails. 17. I can't make a lot of sense about why Gaussian surfaces are special - but that will probably make more sense if we go over any of the chapter in class. Otherwise, my math skills are rusty, but everything looks familiar so I'm not too worried. 18. No problems yet with the reading 19. In Section 23-5, were we supposed to know that the magnitude of charge from the electric field from near the point and from the rest of the charge was the surface charge density / 2Eo? The superposition of these fields makes sense, but I'm uncertain were the values of the fields themselves came from. Question 5: What concerns or issues do you still have with material from previous classes? 1. none 2. 3. 4. none 5. More work on using the equations with Dipoles see #6 6. No concerns or issues. 7. None 8. 9. 10. none 11. none 12. I'm good, I think. 13. 14. None 15. none 16. 17. none. 18. Concerning dipoles, what exactly is the book referring to as p, the dipole moment 19. None, really.