Which of the following is true about electric field lines?

The correct answer is Option (4) → In electrostatics, there are no electric field lines inside a conductor.

An electric field line is drawn so that its tangent gives the direction of the field. The closeness of the lines shows how strong the field is.

Option (1) The magnitude of the field is shown by the length of the arrows on the field lines. — Incorrect. The arrow on a field line only shows the direction of the field. How closely the lines are packed shows its magnitude.

Option (2) The denser the field lines, the weaker is the field. — Incorrect. Field lines crowd together where the field is strong and spread apart where it is weak.

Option (3) Electric field lines start from a negative charge and end on a positive charge. — Incorrect. The field points away from a positive charge and towards a negative charge. So the lines start at positive charges and end at negative charges.

Option (4) In electrostatics, there are no electric field lines inside a conductor. — Correct. In the static situation the free charges of a conductor arrange themselves so that the electric field is zero everywhere inside it. So no field lines pass through the inside of the conductor.

NCERT (2026-27):
Electrostatics of Conductors – “… In the static situation, when there is no current inside or on the surface of the conductor, the electric field is zero everywhere inside the conductor. … In the static situation, the free charges have so distributed themselves that the electric field is zero everywhere inside. Electrostatic field is zero inside a conductor.”