Reading Quiz

Question 1:

Describe an electric dipole.

Answer:

An electric dipole is a special type of charge distribution whereby equal and opposite charges (q) are separated by a distance, d.

An electric dipole is essentially an example of set of charges. In this specific case, the charges have the same magnitude charge, but opposite signs. An electric dipole has a net charge of zero, but there is a field that is created by the dipole because the two point charges are not in the same exact place, thus their separation creates a field
An electric dipole is made up of two point charges that have opposite signs, but equal magnitudes. The overall net charge is zero, but there is an electric field produced by the fact that there is a variation in charge, from the two differently charged ends.
An electric dipole is something that has equal and opposite charge at the two ends. A water molecule is an example of this. The oxygen end of the molecule is negatively charged and the hydrogen end has a positive charge.
An electric dipole has two charges of equal strength, but on opposite ends of the given system
An electric dipole is when an object has 2 point charges of equal magnitude but opposite charge, like a bar magnet
An electric dipole is a set of charges that are equal but have an opposite sign.
A charge distribution consisting of two point charges of negative sign and equal magnitude.
An electric dipole consists of two point charges of opposite sign.
An electric dipole is two point charges of same magnitude but opposite sign.
An electric dipole is a charge distribution that is made up of two equal and opposite point charges.
An electric dipole is a charge distribution comprised of two point charges with opposite signs and equal magnitudes. Its net charge is zero due to the opposite charges. Also, the electric field of an electric dipole is weaker than that of a point charge and results from the separation of the charges.
One of the most important distributions. Consisting of two point charges of equal magnitude but opposite sign.
Electric dipole is a pair of equally and oppositely charged poles.
An electric dipole is a charge distribution that has point charges where the strength of the charge is the same but the signs are different.
A dipole is a charge distribution consisting of tow point charges of equal magnitude but opposite signs.
An electric dipole is a type of electric charge distribution which contains two point charges, one positive and one negative. The two charges in a dipole have the same magnitude, so the net charge of the dipole is zero.
An electric dipole is a combination of two point charges having equal magnitude but opposite signs.
An electric dipole is a set of two point charges of equal magnitude, but opposite sign.

Question 2:

Provide a definition of the electric dipole moment and indicate its direction.

Answer:

The electric dipole moment is represented by the symbol, p, and is equal to the product of the charge (q) and the separation distance (d). Its direction points from the negative charge to the positive.

An electric dipole moment is the electric properties or the effective charge of the dipole. the formula for an electric dipole is p=qd, where q is the charge of the particles, and d is the distance between them.
The electric dipole moment is the product produced when the charge is multiplied by the distance between the two charges that are a part of the dipole. Its direction is from the negative portion toward the positive part.
The electric dipole moment is a vector. Its magnitude is the product of the value of the charge charge (q) and the distance between the two charges (d). It points from the negative to the positive charge.
A dipole's moment equals the product of the charge of one of the poles and the separation between the charges. Its direction is along its axis: + [][][][][][] - Its direction points this way ------>
the electric dipole moment is defined as the magnitude of the charge of the dipole multiplied by the distance between the two charges in the dipole and points from the negative to the positive charge.
The electric dipole moment is the product of its charge and the distance between the two charges that make it up; q*d. The direction is towards the positive (away from the negative).
An electric dipole moment is defined as the product of the charge q and the separation of the two charges which make up the dipole. The direction of this would be from the negative to the positive charge.
The electric dipole moment is the product of charge and distance between two point charges. And its direction is always from the negative charge towards the positive charge.
The electric dipole moment points from the negative charge to the positive one. We have p=qd, q being the charge and d the distance.
An electric dipole moment, p, can be found by multiplying the dipole's charge, q, and the distance between the two charges in the dipole, d [p=qd]. The dipole moment points towards the positive charge from the negative charge in the dipole.
An electric dipole moment is a vector that describes the electric properties of a dipole in general and has a magnitude equal to the product of the distance, d, between the charges and its charge, q. The direction of the electric dipole moment is the direction from the negative charge toward the positive charge.
defined as the product of charge q and the seperation d between the two charges makeing up the dipole. p = qd direction: from the negative toward the positive charge
p=q*d, where p represents electric dipole moment, q represents the charge, and d represents the distance between two points. Its direction is from the negatively charged point toward the positively charged point.
The electric dipole moment is the product of the magnitude of the charges and the distance between them. The direction is from the negative charge to the positive.
The electric dipole moment is defined as the product of the charge and the separation between the two charges making up the dipole. p = qd
The electric dipole moment is a vector whose magnitude is the product of the magnitude of one of the dipole's charges, and the distance between the two charges. Its direction is along the axis of the dipole, pointing from the negative end toward the positive end. The electric dipole moment is the main factor (other than distance) that determines the strength of the electric field generated by the dipole at locations where the distance from the dipole is much larger than the distance between the dipole's two ends.
It is the product of the charge, magnitude q, and distance of separation d between the two charges: p = qd. The direction points from the negative end towards the positive.
The product of the charge q and the separation d between the two charges that make up the dipole. The direction goes from negative to positive.

Question 3:

When looking at the electric field from a dipole from a large distance, compare the field along the dipole axis to that along its perpendicular bisector.

Answer:

E=2kp/x^3 *i, therefore, the field along the dipole axis is twice as strong as the field along the perpendicular bisector at the a given point on both lines
The field along a perpendicular bisector of a dipole, when viewed from a very large distance, is one half that of it along the dipole's axis. There is also a direction change indicated, so it actually varies by -0.5 along the perpendicular bisector versus the dipole's axis.
The field along the axis is twice as strong as the field along the bisector.
Along the axis, the electric field is approximate double that of a dipole's field on a perpendicular bisector.
the field along the dipole axis would appear to fall faster, with a rate of the inverse cube of distance, then the field along its perpendicular bisector, which has a rate of the inverse square of distance
Given =-(kp)/(y^3) and =(2kp)/(x^3), the field along the axis is twice as strong as the field along the dipole's perpendicular bisector.

The field along the dipole axis is twice as strong as the field along the perpendicular bisector.

The electric field along the dipole axis is twice the field along its perpendicular bisector.

The electric field is approximately twice as strong along the dipole direction than along its perpendicular bisector.

When looking at the electric field from a dipole from a large distance, the field along the dipole axis is twice as strong as the field along its perpendicular bisector.

The field along the dipole axis is approximately twice the strength of the field along the perpendicular bisector.

dipole field for y >> a, on a perpendicular bisector: E = -kp/y^3*i dipole field for x >>a, on axis: E = 2kp/x^3*i the field along dipole axis at a given distance is twice as strong as along the bisector

The electric field along the axis is twice as strong as the one along is perpendicular bisector.

The electrical field points in opposite directions. Along the dipole axis the electric field points towards the negative charge.

The field should be stronger along the dipole axis than the perpendicular bisector, because along the perpendicular axis, more of the forces are canceling each other out.

At a large distance from the dipole, the electric field along its axis is twice as strong as that along its perpendicular bisector.

The field along the dipole axis is stronger and of the opposite direction than along its perpendicular bisector.

Along the dipole axis, there is torque, but along the perpendicular bisector there is no torque.

Question 4:
The electric field is approximately twice as strong along the dipole direction than along its perpendicular bisector.
I think that this question is actually the answer to the above question?

This might be the answer to question 3. Or this is what I was attempting to get at in my response.

Yes. This wasn't a question. I might be making a dumb mistake--as in I might be misreading it--because I'm kind of tired and out of it and I read the word "genetic" as "generic" a couple minutes ago, which totally changed the meaning of the sentence. But as far as I can tell, this is just a true statement.

equations 20.6?

This is because the dipole is not spherically symmetric and its field depends not only on distance but also on orientation.

Yes, this is true.

???

True!

This is the answer to question #3.

This is the answer for the previous question. Because at perpendicular bisector direction, the electric fields of postive and negative charges cancel each other. But at the dipole direstion, the electric fields of postive and negative charges are the same: from the negative toward the positive charge.

Yes.

Yes.

True.http://www.eg.bucknell.edu/cgi-bin/cgiwrap/koutslts/rq?no=01

True. E=kp/y^3 on perpendicular bisector and E = 2kp/x^3 on axis.

Question 5:
What happens to an electric dipole in the presence of an external electric field?
Answer:
The dipole experiences a nett torque or twisting action.
When a dipole is in the presence of an external electric field, the dipole will be unaffected, because it has a net charge of zero. However, the dipole's field will be less effective than the electric field at larger distances because the electric field follows the inverse square law, while the dipole field follows the inverse cube law.

In the presence of an external electric field, the electric dipole will undergo a net torque, but no application of a net force.

It aligns itself so as to reduce the net field. So if the electric field points up, say, then the dipole is going to align itself so that its own field points down.

It aligns itself along the vector lines of the field.

if the electric field is uniform, the electric dipole does not have any net force due to the electric field, but it does experience torque with aligns the dipole with the electric field. If the electric field is not uniform, the dipole experiences a net force and torque

There is no net charge on the dipole because it has equal but opposite charges, but the the dipole rotates clockwise due to a torque that aligns the dipole with the electric field.

The electric dipole experiences a torque which rotates the dipole until its aligned with the electric field.

When an external electric field is present, an electric dipole experiences a torque.

In presence of an electric field, the dipole tends to align itself to the field.

An electric dipole experiences a torque and a potential net force when in the presence of an external electric field. If the field is uniform, the dipole will experience a torque that aligns it with the field, but will not experience a net force. If the field is not uniform, the dipole will experience a similar torque and a net force.

In the presence of a uniform external electric field, the dipole aligns with the electric field (the direction from the negative charge to the positive charge being the same as that of the electric field) due to electric forces that are equal in magnitude and opposite in direction acting on the charges, and the net force acting on the dipole is zero. The work done by the electric field in turning the dipole is stored as potential energy. In an electric field that is not uniform, there is a net force acting on the dipole as well as torque because the electric forces are either not equal in magnitude, are not always in opposite directions, or both.

A dipole in a uniform electric field experiences a torque, but no net force. When the electric field differs in magnitude or direction at the two ends of the dipole, the dipole experiences anonzero net force as well as a torque.

If the external field is strong enough, the dipole will change the direction. (I suppose it's talking about the situation like, I have a magnetic compass on the earth.)

It experiences a torque and the dipole rotates.

The dipole is rotated to be oriented with the field.

In an external electric field, a dipole will rotate in order to align itself with the field. The end with a charge opposite that of the field source will be pulled toward the source, while the end with a charge like that of the source will be repelled from the source, producing torque on the dipole.

The dipole will experience a torque, causing it to align itself with the field appropriately.

The electric experiences a torque in the presence of an external electric field.

Question 6:
Describe the characteristics and give three examples of (a) a conductor; (b) an insulator.
Answer:
For conductors, charge is free to move around in the presence of an electric field. Examples are metals, water, ionised gases. For insulators, charges cannot move. Such examples are glass, rubber, and felt.
A). gold, copper, steel B). rubber, water, plastic

(a) Conductor: A material that allows charge to readily transmit and carries electric current well; examples include aluminum, iron and gold. (b) Insulator: A type of matter that does not allow charge to travel through easily and does not transmit electric current well. Examples will include: plastics, rubber and water.

a) A conductor is matter that individual charges can move through. The obvious example is metal. People often think that water is a conductor (they make you get out of the pool when there's a thunder storm), but it isn't. It's the ions in the water that conduct the electricity. Gases can also be ionized. b) An insulator is matter that charge cannot move through. They can still contain charge, but the charges are bound into neutral molecules. When an electric field is applied, intrinsic dipoles will align. Other molecules may have induced dipole moments, meaning that the application of an electric field makes the molecules stretch so that they act like dipoles. Examples of insulators would be distilled water, plastic, and glass.

In conductors, electrons are free to move from atom to atom. In insulators, they are not as free to move. Conductors: Copper, Iron, Water Insulators: Rubber, Wood, Air

conductors are materials in which an electric current can flow through it, while insulators are materials in which charge is not free to move. Insulators have a neutral charge. Conductors: iron, aluminum, and bronze. Insulators: glass, rubber, and wood.

Conductors are materials in which the charges are able to move and create a flow of current, where insulators are materials that do not enable the motion of charges. Metals, salts (in solution), and ionized gases are conductors, and glass, plastics and clay are good insulators.

(a) In a conductor individual charges are allowed to move throughout the material. eg - metals,ionic solutions, ionized gases (b) An insulator is a material in which charges are not free to move about since they are bound to neutral molecules. eg- water, plastic, air

In conductors, electric charges move in ordered motion when an electric field is applied_for example, wire, gold , iron. But in insulators, electric charges are not free to move and thus they can't conduct electricity. For example, wood, rubber, paper.

A. A conductor is a material in which charges are free to move. e.g: copper, gold, aluminum. B. An insulator is a material in which charges are not free to move. e.g: ceramic, PVC, glass.

A conductor is a material that can hold a current, as charges are able to move freely. Examples of conductors include metals, ionized gases, and ionic solutions. An insulator is a material that cannot hold a current as charges are not able to move freely. Examples of insulators include glass, rubber, and paper.

(a) A conductor is a material in which charges are able to move freely. If an electric field is present, the charges in the conductor move to create an electric current. Three examples of a conductor are silver, copper and aluminum. (b) An insulator is a material in which charges are not able to move freely. The charges in an insulator are part of neutral molecules, but the presence of an electric field could create induced dipole moment. Three examples of insulators are glass, Teflon, and porcelain.

Conductor: some matter that individual charges are free to move throughout the material. ie. metals, ionic solutions, and ionized gases Insulator: materials in which charge is not free to move. ie. pure water, wood, porcelain, and neutral molecules.

(a) Conductors are the materials that can hold electric current. e.g.) Salt water, metals, diamonds (b) Insulators are the materials in which electric charges are not free to move. e.g.) Paper, rubber, glass

a) individual charges can move freely within the material b)individual charges cant move

(a) On conductors, electrons are able to freely move. Metal, water, and anything at absolute zero. (b) On an insulator, electron cannot freely move about the surface, but they are able to move onto other surfaces upon contact. Fur, glass, balloons.

A conductor is a material whose constituent charges (protons, electrons, and/or ions) are free to move, and thus can produce an electric current in the presence of an external electric field (even if the conductor as a whole is electrically neutral). Three examples of conductors are metals, ionic solutions, and ionized gases. An insulator is a material whose constituent charges are not free to move, and thus cannot produce an electric current. Three examples of insulators are wood, rubber, and pure water.

a. conductors allow current to flow freely through the material, the electrons are generally the point charges that do the movement, different materials allow conduction more easily. Examples: copper wire, ionized gases (ie neon signs), other metals. b. insulators resist the flow of electric current. Insulator molecules typically have their highest level of electrons full, requiring a very large amount of energy to excite an electron to the next level. Such a level of energy is usually accompanied by physical or chemical changes in the material (ie a voltage through rubber so high that it starts to melt). Examples: rubber, glass, ceramic

A conductor is a material in which charge is free to move through it. Three examples are copper, aluminum, and impure water, An insulator is a material in which charge is not free to move through it. Three examples are rubber, glass, and Teflon.

Question 7:
Explain how you would go about calculating the electric field produced by a randomly-shaped distribution of charge.
Answer:
One would use the superposition principle and break up the distributions into a series of point-like charges. The resulting electric field would be the linear combination of all the mini-electric fields.
To calculate the electric field produced by a random shape distribution of charge, you would have to break up the random shape into point sized particles, calculate their individual fields, and then add all of the fields together to get the overall electric field

In order to calculate the electric field produced by this random distribution, it is necessary to divide the area into a large number of very small charge portions 'dq', which, when multiplied by unit vector "r-hat", and 'k', Coulomb's constant, and divided by the square of the distance between the charges, r^2, and integrated, the small parts are essentially summed, which would lead to the electric field produced by this distribution.

I would sum the fields of the point charges.--I would find the field produced by the charge dq and integrate over the limits of whatever the shape was.

You would sum the electric fields produced by small sections of the distribution.

You would sum up all the electric fields of the object by taking the electric fields of small charge elements, dq.

To calculate the electric field of a randomly shaped charge distribution, I would divide the shape into tiny pieces that the charge can be determined of, then integrate all of the small pieces to determine the total field.

Calculate the vector sum of the fields dE which arise from the individual charge elements dq. All these are calculated using the appropriate distance r and unit vector.

The electric field at a point produced by a randomly-shaped distribution of charge is the vector sum of the electric field produced by individual charges on that object.

Divide the object in several ones of similar distribution of charge, then calculate the electric field produced by each of those objects, and using superposition we add them to find the net electrical field.

It is almost impossible to calculate the electric field produced by a randomly-shaped distribution of charge. Because of this, it must be assumed that the distribution is continuous, in which case the field is calculated by adding up the fields at each respective charge element- thus taking the integral of all the fields. (integral of (kdq)/(r^2) * (r hat) )

First, I would pick an appropriate coordinate system. Next, I would put a field point on the x-axis and estimate a distance, r, from a point charge (I would need to pick a very small area) to my field point. Using E = k*q/r^2 (for the magnitude of E)and unit vectors (using y/r and x/r), I would add more and more field vectors to eventually find a reasonable calculation for the electric field as a vector sum. If possible, I would put the field point on the x-axis far enough away from the distribution of charge so that x>>y and y could be neglected without creating a major error in the calculation. Knowing the net charge, Q, of the distribution of charge, I would then integrate dE (as a vector), which is then k*dq/x^2 * x/r. E would then be about k*Q/x^2 the further I went away.

Divede the charge region into very many small identical charge elements. Each of these indentical charges produce a electric field dE = k*dq/r^2*r. Then integrate E = (mark look like f) dE.

Take a point at the randomly-shape material, calculate the field depending on that point, repeat it for all the points in the material, and sum them up. i.e. Take the integral of all electric fields.

Use an integral to calculate the electric field.

Integrals, or reiman sums if you don't know calculus.

I would place the shape in a coordinate system and integrate along the shape within this coordinate system, using the volume/surface/line charge density and the definition of the electric field of a point charge in reference to a field point.

Take the sum of the point charges of the distribution, which would create an integral over the entire charge distribution.

Using integration, add up all the fields of individual point charges.

Question 8:
POLL #1: What do you think is more amazing: that charge is conserved or that the electric fields they produce obey the superposition principle? Give reasons for your response.
Answer:
This is a tough one.
I think that the fact that charge is conserved is more impressive, because a general look at electricity or visible electricity would make it seem that charge could easily dissipate into the atmosphere

The superposition principle is most amazing to me, in that it allows many scenarios found in the universe to be broken down into vectors that easily and somewhat quickly allow us to solve problems that would otherwise be too difficult or time consuming. Its a manifestation of the elegance of physics to describe the universe. The conservation of charge, like other conservation laws, is also supremely elegant, however.

I think superposition is pretty amazing (though I did not wake up in a cold sweat luckily). It's amazing that you can put something with no net charge under the influence of an electric field and it will align itself so as to cancel out as much of the field as it possibly can. That just blows my mind. Why are is matter so intent on being neutral?

The superposition principle is more amazing, since it allows the production of very complex fields through relatively simple yet sound mathematical processes.

That the electric fields obey the superposition principle because you would think that because there are so many particles that they would all interfere with each other so that no clear sum of forces could be done, and the fact that imaginary fields are vectors that can be added is weird.

I think it's amazing that charge is conserved in a closed region, especially because particles can be created and destroyed. We have become used to a conservation of energy model of the world, but why don't charges float away? Why don't they spread out or travel through the boundaries of the field? And although particles can be created and destroyed, they must always come and go in pairs to keep the charge constant.

I find it more amazing that the electric fields produced by charges obey the superposition principle. Due to the fact that this principle is obeyed, the electric field of objects of irregular shapes can be found. The fact that vectorial addition and subtraction of electric fields is possible is amazing.

Conservation of charge is more amazing because almost every physical quantity (size, force, mass, light intensity...) we know in life is adjustable but we can never have one and a half charge. Charge seems to be the only exception among our everyday experience.

The superposition principle, as it seems it is a law that appears in several levels, such as gravity and regular forces.

I think it is more amazing that electric fields that charges produce obey the superposition principle, as no matter the size or location of the charge, the field that it creates can be added vecorally with the field that another charge creates in order to create a sort of "net field," which would then only be added vectorally to another charge's field, making a constant or unchanging net field between many different charges seem almost impossible.

I think that the fact that electric fields obey the superposition principle is more amazing. Adding up vectors allows calculations to be relatively simple, and therefore a vast number of natural phenomena can be described quantitatively without a complicated formula. Also, studying electric fields is made easier by introducing familiar concepts like vector addition.

the electric fields they produce obey the superposition princile, because the charge is conserved is more like a conservation rule that no new material could be produce with nothing, but the electric field that is not available to touch and see obeys the rule! It's quite amazing...

I think that conservation of charge is more amazing that the superposition principle because the fact that charge is conserved may possibly be used for some sort of semi-eternal energy making (I guess it would be true since nobody has made the system, but I wish there exists a system like that).

Superposition principal is "more amazing" because it seems natural that charge is conserved and superposition makes me thing of mechanical forces and not electric fields.

The fact that charge is conserved doesn't seem that amazing, because everything else in the universe is conserved.

I think it is more amazing that charge is conserved, because we don't really know what charge is or where it comes from, so we don't have any reason to assume that it would be. It would be perfectly plausible for charge to disappear by converting to some form of energy, or vice versa, and it is intriguing that this is not the case.

All the worlds electronics function because charge is conserved, and electrons can flow freely to create a current powering all sorts of devices, from iPods to pacemakers. Without that simple principle, I would be writing this on paper by candlelight, instead of typing by a lamp.

I think the fact that charge is conserved is more amazing. The fact that charge is conserved and quantized is somewhat astounding just because it is really interesting that the world works like that.

Question 9:
Please describe any part of the reading that was unclear.
The end of the reading about the Continuous Charge Distribution was somewhat confusing I thought

The reading was reasonably clear for me. I think it'll be most important for me to go back and go through some more of the example problems so that I'm sure I understand exactly what I was reading.

I think it all had an equal degree of clarity. I generally learn something better if I hear someone talk about it and then read about it afterward. And I'm especially not very good at learning physics from a book. I think this is partially because my teacher last year lectured really well and it was much easier than this year's physics (not surprisingly) so I picked it up fast. I literally only opened the textbook once when I had missed class.--I haven't had much practice learning physics from a book. I do better when someone's lectured or explained it and then I go and read the book and I'm like "Oh, this makes sense!" or "Oh, I remember this!" Instead of having to read the same thing a bunch of times before I'm like, "Oh, yeah...This is kind of like what Gary (my physics instructor last year) was talking about when we were doing the unit on electricity last spring..." or "Oh...well, I guess that makes sense." But I pretty much get it now.

Is the direction of a dipole along its axis? If so, which way does it point, positive or negative?

The summing of the individual electric fields is a little confusing

I don't think I fully understood the first part of 20.4 on field points.

The part about the volume charge density and line charge density and the following example using the above mentioned quantities was unclear.

I am not quite clear about dipole moment.

Example 20.6

I would like to go over how you can tell when to use y/r vs. x/r when deconstructing a "r hat". Also, it would be nice to go over dipole moments and reemphasize the superposition principle.

No parts of the reading were unclear.

the last two pictures on page 341, and dieletrics part on p340

I don't really get how dielectric breakdown occurs.

In the section on conductors, insulators and dielectrics, it was unclear in which category a dielectric belongs--is a dielectric a type of insulator, or is it in a category by itself?

Nothing this time.

Some of the dipole in an electric field material was unclear.