State four properties of electric field lines. Draw the field lines for (a) an electric dipole and (b) two equal positive charges.

1. 1 · Define a field line. A curve whose tangent at any point gives the direction of the electric field there.
2. 2 · Give four properties.
   • Start on positive and end on negative charges.
   • Never cross each other.
   • Never form closed loops.
   • Crowd where the field is strong.
3. 3 · Draw the dipole pattern. [+q and −q; curved lines from +q to −q, a straight line along the axis, arrows from + to −]
4. 4 · Draw two equal positive charges. [Two +q charges; lines bending away from each other; neutral point marked midway]
5. 5 · Close in one line. Field lines give the direction of the field, and their crowding gives its strength.

Scoring tip: Put arrows on every line and mark the neutral point. Diagrams without arrows lose marks.