# Help - Electric Field Questions

• DetroitDJ
In summary, the conversation is discussing two questions on a homework assignment that the speaker is struggling with. The first question involves finding the charge on a circular segment of an electrode, while the second question involves determining the surface charge density of an infinite charged plane and the time required for an electron to travel a certain distance. The speaker's method for the first question involves using the formula for electric field of a disk, but they are unsure of the correct equation to use. For the second question, they suggest considering the force to find the acceleration and then using the same equation as the first question to determine the surface charge density.
DetroitDJ
There's two questions on my current homework assignment that I keep getting the wrong answer too (the answer input site tells me it's wrong, but has nothing on why or any hints or anything). If someone could be so kind to walk me through how to solve these, I'd be really grateful.

The electric field strength 4.00 cm from a very wide charged electrode is 4000 N/C. What is the charge (in nC) on a 1.10 cm diameter circular segment of the electrode?

My method for that one so far has been utilizing the formula for the electric field of a disk, solving for Eta and using Eta in Eta=Q/A to find Q - but that's somehow wrong.

An electron is released from rest 2.0 cm from an infinite charged plane. It accelerates toward the plane and collides with a speed of 1.0*10^7 m/s. What is the surface charge density of the plane? What is the time required for the electron to travel the 2.0 cm?

Basically the same problem, but from a different point of view. Same trouble.

For the first part, your equation is wrong for E, it should be E=Q/2$\epsilon_{0}$A, or E=$\sigma$/2$\epsilon_{0}$, where $\sigma$ is the surface charge density. What is Eta? Find out the surface charge density, then use that to find the charge on the circular segment. I'm not sure about this actually, as I haven't used the distance from the electrode- I assumed the electric field was constant, I can't see why it wouldn't be.

For the second part, you can find the acceleration, and hence the field strength, by considering the force. Then getting $\sigma$ should be fairly simple, it's the same eqn as the first part.

Hi there,

I understand that you are having trouble with two questions on your current homework assignment regarding electric fields. I would be happy to walk you through the steps to solve these problems.

For the first question, you are given the electric field strength and distance from a charged electrode and are asked to find the charge on a circular segment of the electrode. Your approach of using the formula for the electric field of a disk and solving for the charge is a good start. However, it seems like you may be missing a key step in your calculations.

To solve this problem, you first need to calculate the area of the circular segment using the given diameter. Once you have the area, you can plug it into the formula Eta=Q/A and solve for Q. Make sure to pay attention to the units and convert them accordingly. If you are still having trouble, I would suggest double-checking your calculations and units to ensure they are correct.

For the second question, you are given the initial and final velocities of an electron released from rest near an infinite charged plane and are asked to find the surface charge density and time of travel. To solve this problem, you can use the equations for electric force and kinetic energy to set up a system of equations. You know that the electric force is responsible for the acceleration of the electron, and the kinetic energy is converted from the electric potential energy. By setting these equations equal to each other and plugging in the given values, you can solve for the surface charge density and time of travel.

I hope this helps guide you in the right direction for solving these problems. If you are still having trouble, I would suggest reviewing your understanding of electric fields and their related equations. It may also be helpful to consult with your teacher or a classmate for additional support. Good luck with your homework!

## 1. What is an electric field?

An electric field is a physical field that is created by electrically charged particles and exerts a force on other charged particles within its range. It is represented by arrows that indicate the direction of the force and its strength at various points in space.

## 2. How is the strength of an electric field measured?

The strength of an electric field is measured in units of newtons per coulomb (N/C). This tells us the amount of force that is exerted on a single unit of charge in the field. The closer the electric field lines are together, the stronger the field is at that point.

## 3. What factors affect the strength of an electric field?

The strength of an electric field depends on the magnitude of the charge creating the field and the distance from that charge. The field strength decreases as the distance from the charge increases. It also depends on the medium in which the field exists, as some materials can affect the strength of the field.

## 4. How is the direction of an electric field determined?

The direction of an electric field is determined by the direction in which a positive test charge would move when placed in the field. This is because electric field lines always point away from positive charges and towards negative charges.

## 5. How is an electric field different from an electric potential?

An electric field and electric potential are closely related but have distinct differences. Electric potential is a measure of the potential energy that a charged particle has at a specific point in the field, while electric field measures the force exerted on a charged particle at a specific point. Electric potential is a scalar quantity, while electric field is a vector quantity.

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