Electric Field

• Jan 24th 2011, 11:28 AM
quantoembryo
Electric Field
I just have a couple of questions concerning electric field.
http://i49.photobucket.com/albums/f2...g?t=1295893638
Perhaps someone could just tell me whether or not I have a grasp on this conceptually?

Is the electric field in the direction of path zero at every point from a to b in a straight line?
I would suggest that if you were to make a line segment from a to b, the only position along that line where the electric field would be zero, is in the middle where the line is perpendicular to the line of force.

What about along the equipotential line joining a-b?
The electric field would be zero along this line..

Is the electric field in the direction perpendicular to the path zero in the straight line joining a-b?
I would say no. It is never zero along this line.

What about the equipotential line joining a-b?
Definitely never zero.

• Jan 24th 2011, 01:14 PM
HallsofIvy
The "electric field" is an assignment at each point of a vector showing the direction the electric force would push a single electron. The length of the vector is the force on that single electron. At points where the electric field is 0, the force vector is the 0 vector which has NO length and so there is no direction associated with it. I see nothing on your picture to indicate field strength (or field strength 0) at any point.

I don't know what you mean by "the electric field in the path 0". The electric field is the entire picture. There are individual force vectors at individual points but not an "electric field" at a point. Equipotential paths are always perpendicular to the electric field curves. Be careful about saying "equipotential line". The equipotential "paths" or "curves" are NOT straight lines here. And thy path joining a-b does NOT look like a straight line.
• Jan 24th 2011, 01:43 PM
quantoembryo
These questions were given to me on an assignment, and they have me baffled. There is no refference point, however, equipotential path has a potential difference of 1 V. Are you saying that my answers are wrong?
• Jan 24th 2011, 02:26 PM
quantoembryo
Here, I will rephrase my answers. Keep in mind equipotential curves are separated by a potential difference of 1 V. There is no given reference point. Additionally, I will quote the questions being asked...

"Is the electric field in the direction of the path zero at every point on the path from A to B along a straight line?"

"Is the electric field in the direction of the path zero at every point on the path from A to B along the equipotential line that goes through both points?"

"Is the electric field in the direction perpendicular to the path zero at every point on the path from point A to point B along a straight line?"

"Is the electric field in the direction perpendicular to the path zero at every point on the path from point A to point B along the equipotential line that goes through both points?"

These are the questions, and their exact quotes.
• Jan 25th 2011, 07:37 AM
quantoembryo
I'd just like to state that this is a new concept to me, and that I'm trying to understand it conceptually. Although answers for this are mulitple choice Y/N, I want to ensure I have grasped the concept.

"Is the electric field in the direction of the path zero at every point on the path from A to B along a straight line?"
If one were to construct a line segment joining point A and point B, one could conclude that NO the electric field is not zero at every point along that path. The only point along that segment where the electric field is perpendicular to the line, would be in the middle.

"Is the electric field in the direction of the path zero at every point on the path from A to B along the equipotential line that goes through both points?"
YES.

"Is the electric field in the direction perpendicular to the path zero at every point on the path from point A to point B along a straight line?"
No. In fact, never.

"Is the electric field in the direction perpendicular to the path zero at every point on the path from point A to point B along the equipotential line that goes through both points?"
No, the resulting electric field vectors would be perpendicular to the equipotential path. Therefore, it is the greatest at these points.
• Jan 25th 2011, 08:57 AM
Unknown008
This is a strange way to ask those questions indeed. I had to re-read your posts to make sure what you were trying to say.

There is an electric field everywhere in your picture, without exception.

What is or is not 0, is the electric force experienced in a particular direction.

When you go along the lines (arrows really), there is a change in potential, hence, a force is experienced in this direction.

When you go perpendicular to the field lines, there is no change in potential and hence, no force is experienced in that particular direction.

Force and field are completely different things.
• Jan 25th 2011, 06:05 PM
quantoembryo
Yes, but if there is no force along a curve, then there is no field, correct? For example, if you move along an equipotential surface, you are not changing its potential, and therefore the force tangent to the curve is zero, and consequently the field is zero since E=F/q. As far as I can tell, my answers are correct on a yes no basis, considering the questions state "along the path" meaning tangent to whichever path they are referring to, whether it is the equipotential curve, or the straight line segment joining A and B.
• Jan 25th 2011, 08:28 PM
SammyS
Quote:

Originally Posted by quantoembryo
I just have a couple of questions concerning electric field.
...

Perhaps someone could just tell me whether or not I have a grasp on this conceptually?

Is the electric field in the direction of path zero at every point from a to b in a straight line?
I would suggest that if you were to make a line segment from a to b, the only position along that line where the electric field would be zero, is in the middle where the line is perpendicular to the line of force.

I agree with you. (∴ you are correct. LOL) Going from point A to point B in a straight line: The only position along that path where E is perpendicular to the direction of the path is at the mid-point.

Quote:

What about along the equipotential line joining a-b?
The electric field would be zero along this line..
I would state this a bit differently, but ... The electric field, E, is perpendicular to this path at all points, so there is no component of E parallel to this path.

Quote:

Is the electric field in the direction perpendicular to the path zero in the straight line joining a-b?
I would say no. It is never zero along this line.
You are correct!

Quote:

What about the equipotential line joining a-b?
Definitely never zero.
Also correct. In fact the ⊥ component is constant as well as non-zero.