What do electric field lines illustrate about the field?

What do electric field lines illustrate about the field?

• A. The direction of the electric field; the density indicates magnitude
• B. Only the magnitude
• C. Only the direction
• D. They do not illustrate the field

Answer: (A)

Electric field lines are a visual map of a vector field. The direction of the field at any point is given by the tangent to the line there, so following a line shows the field’s direction. The density of lines in a region—how close the lines are—reflects the field’s strength: more lines per area mean a stronger field, fewer lines mean a weaker field. Lines also start on positive charges and end on negative charges and never cross, which keeps the representation unambiguous. So they illustrate both the direction and the magnitude (via density) of the field. The other statements are incomplete because they ignore either the directional information or the magnitude information, or claim no field is illustrated at all.

Electric field lines are a visual map of a vector field. The direction of the field at any point is given by the tangent to the line there, so following a line shows the field’s direction. The density of lines in a region—how close the lines are—reflects the field’s strength: more lines per area mean a stronger field, fewer lines mean a weaker field. Lines also start on positive charges and end on negative charges and never cross, which keeps the representation unambiguous. So they illustrate both the direction and the magnitude (via density) of the field. The other statements are incomplete because they ignore either the directional information or the magnitude information, or claim no field is illustrated at all.