D.2.7—Electric field lines
- Syllabus
- First assessment 2025
- Objective
- —
- Level
- HL
Read Electric Field Lines
Interpret a field line
Electric field lines show the direction of the force on a small positive test charge. Their arrows point away from positive charges and toward negative charges. The tangent to a line gives the local field direction.
| Required geometry | Electric-field pattern |
|---|---|
| Single point charge | radial; outward for positive, inward for negative |
| Two point charges | resultant curves; from positive toward negative; lines never cross |
| Charged spherical conductor | radial outside and normal to surface; no field lines in conducting material or an empty shielded cavity |
| Opposite parallel plates | straight, parallel central lines from positive to negative; curved edge lines show fringing |
Read qualitative strength
Where field lines are closer together, the field is stronger; where they spread out, it is weaker. This is a qualitative representation unless the diagram specifies equal field-line intervals or a scale.
Common trap
Do not point electric field lines from negative to positive, make them cross, or draw them tangent to equipotential surfaces. Field lines follow the positive-test-charge convention.
D.2.7 Exam Analysis
Assessment in practice
1–2 marksHow it is assessed
Questions judge correct field-line statements or ask you to draw lines between charged plates.
Command terms
Which / Draw
What earns marks
Point arrows in the positive-test-charge direction, keep lines non-crossing, and use density to compare qualitative field strength.
Watch for
Drawing arrows from negative to positive or allowing lines to cross; also confusing line density with the number of charges.
Representative question
Question 1
[Maximum number: 1]
The diagram shows the electric field pattern due to two point charges X and Y . Y is a negative charge.
Which of the following correctly identifies the charge X and the direction of the electric field?
Sign of charge X
Direction of electric field
positive
Y to X
positive
X to Y
negative
X to Y
negative
Y to X
B