Help - Electric Field Questions

[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.

 

[Tomsk]

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.

 

[kyle8921]

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!