# Field lines from a line of charge

• vikasagartha
In summary, the conversation discusses how Gauss's law can be used to calculate the electric field of a cylindrical shape, but it only applies to the surface of the cylinder and not along the cylinder itself. This is because the field lines directed along the cylinder get canceled out by opposite fields produced on either side. The surface area of the circles in the cylinder is neglected because there is no electric field passing through them. It is also mentioned that Gauss's law only applies to infinitely long cylinders due to symmetry.
vikasagartha
I have a general gauss' law/electric field question.

In calculating the electric field of a cylindrical shape, gauss' law can be applied to find that the Electric field only points aways from the surface of the cylinder (aka, in the s-hat direction). But this means that there are no field lines directed along the cylinder...why isn't there a field line that points directly up or down along the z axis? For a finite cylinder, this would make sense to me. However, whenever you are calculating the E field via gauss' law, you neglect the surface area of the circles in the cylinder...can someone please clarify why this is? I have taken it for granted for a long time but never really understood...

vikasagartha said:
But this means that there are no field lines directed along the cylinder...
There are. But they get canceled out since two points on the conductor on either side of your point of consideration produce electric fields in opposite directions.
vikasagartha said:
..you neglect the surface area of the circles in the cylinder...can someone please clarify why this is?
Because there is no electric field passing through these circles. Reason same as above. Along the cylinder is nothing but perpendicular to these circles.

Gauss's law only helps if it is an infinitely long cylinder so that symmetry suggests there is no longitudinal E field.

## 1. What are field lines from a line of charge?

Field lines from a line of charge are imaginary lines that represent the direction and strength of an electric field created by a charged line. They show the path that a positive test charge would follow if it were placed in the electric field.

## 2. How are field lines from a line of charge different from point charges?

Field lines from a line of charge are different from point charges because they extend infinitely in both directions along the line of charge, while point charges have field lines that extend outward in all directions. Additionally, the electric field strength decreases at a slower rate with distance for a line of charge compared to a point charge.

## 3. What factors affect the shape and direction of field lines from a line of charge?

The main factor that affects the shape and direction of field lines from a line of charge is the magnitude and direction of the charge itself. Additionally, the distance from the line of charge and the presence of other charges in the surrounding area can also impact the shape and direction of the field lines.

## 4. How can field lines from a line of charge be used to determine the electric field strength?

The electric field strength can be determined by the density of field lines. The closer the field lines are to each other, the stronger the electric field. The electric field strength also decreases as the distance from the line of charge increases.

## 5. Can field lines from a line of charge intersect with each other?

No, field lines from a line of charge cannot intersect with each other. This is because the electric field at any given point can have only one direction and strength. If the field lines were to intersect, it would imply that the electric field at that point has two different directions and strengths, which is not possible.

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