Physics · Electric Charges And Fields · NEET
No. They are an imaginary drawing tool to picture the electric field, which is a vector at every point. NCERT says only the RELATIVE number of lines matters, not the exact count. We draw them so the tangent shows field direction and the crowding shows field strength. The field itself is real and continuous; the lines are just a map of it.
If two lines crossed at a point, you could draw two different tangents there, meaning the electric field would point in two directions at once. But the field at any point has only ONE unique direction. So a crossing is impossible. This is a very common NEET one-liner test.
The field points away from a positive charge (a test charge +q feels a push outward) and toward a negative charge (pulled inward). Since a field line follows the field direction, it must leave a positive charge and enter a negative charge. If only one charge is present, the other end goes to infinity.
By their crowding. Where lines are close together (dense), the field is strong; where they are far apart, the field is weak. Near a point charge the lines bunch up, so E is large; far away they spread out, so E is small. In a uniform field the lines are equally spaced parallel straight lines.
No. Electrostatic field lines are never closed loops — they always start and end on charges (or at infinity). This is because the electrostatic field is conservative. Note: magnetic field lines DO form closed loops, so do not mix the two up.
Usually no. A field line gives the direction of force on a charge at each point, but the charge moves along the field line only if it starts from rest and the line is straight. For curved lines the charge gains sideways velocity and does not stay on the line, so the line is not its trajectory.
If the closed-surface integral of E over a surface is zero (net flux = 0) over a closed surface, then:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is a curve drawn so that the tangent at each point gives the direction of the electric field E at that point, with an arrow showing which way E points.
1) Continuous curves with no breaks. 2) Start on positive charges, end on negative charges (or at infinity). 3) Two lines never cross. 4) Never form closed loops (electrostatic). 5) Crowded where E is strong, spread out where E is weak. 6) In a uniform field they are parallel, equally spaced straight lines.
The number of lines crossing a unit area perpendicular to them is proportional to E. Close spacing means many lines per unit area, so E is large. This links directly to the flux idea (flux is proportional to E times area).
The lines leave each positive charge, then bend away from the region between the charges (they repel), with a neutral point in the middle where the field is zero and no line passes.
Electric (electrostatic) field lines are open — they begin and end on charges. Magnetic field lines always form continuous closed loops because isolated magnetic poles do not exist.
