Draw electric field patterns around point charges
Draw radial outward fields for positive point charges and radial inward fields for negative ones using the positive-charge convention.
Section P4.2.1 · Electric charge
Exam scope and assessment notes
Mapped to the named 0973 section using teaching from the corresponding single-science course. A 0973-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade. This qualification reports two grades on the 9–1 scale; confirm the entry route for your zone and exam series.
Before you begin
- Use the positive-test-charge convention.
- Distinguish schematic spacing from numerical calibration.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What defines local field direction?
What you will learn
- Draw isolated positive and negative point-charge patterns.
- Explain radial direction without claiming uniform strength.
Use radial lines and correct arrow sense
For an isolated positive point charge, representative field lines extend radially outward. A positive test charge is repelled away, so arrows point away from the source. For an isolated negative point charge, lines point radially inward because the positive test charge is attracted toward the source.
Distribute rays around the whole source rather than drawing only one straight path. Each local arrow follows its ray. Lines do not cross and are not closed magnetic loops in this single-charge sketch. The ideal point model concerns the external region rather than the internal structure of a real particle.
Separate pattern and strength
Equal angular spacing between rays represents spherical symmetry. It does not make the field uniform: the representative lines spread apart as distance from the source increases. A finite flat sketch is a cross-section of a three-dimensional radial pattern and does not count the actual number of physical lines.
Place an actual test charge at the stated position and use its sign to obtain its force. On the right of a positive source, field points right; an electron there is forced left. No distance law or numerical force is required or inferred from the chosen ray count in this pattern lesson.
Sources for this lesson
Pause and explain
Just above an isolated negative point source, what is the field direction?
Worked example
Draw the field of an isolated negative point charge and give the field direction just to its right.
Show the worked solution
- Use radial lines around the source.
- Point arrows inward for a negative source.
- On the source's right, inward means leftward.
Answer Radial inward pattern; the field immediately to the right points leftward.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Describe a complete field sketch for an isolated positive point charge.
Give me a hint
Include rays around the source and arrowheads along them.
Compare my reasoning
- Place the positive source at the centre.
- Draw non-crossing radial lines distributed around it.
- Point all field arrows outward.
Non-crossing radial lines with outward arrows around the positive source.
Look for these in your work
- Cover more than one side.
- Use the positive-test-charge convention.
For a negative point source, give the field direction at a point to the left and at a point below it.
Give me a hint
Both arrows point toward the source from their respective positions.
Compare my reasoning
- At the left, inward is rightward.
- Below, inward is upward.
- The local direction depends on position.
Left point: rightward; lower point: upward.
Look for these in your work
- Use each stated position.
- Keep both arrows directed inward.
Eight equally angled rays surround a positive point source. Does that show a uniform field, and which way is an electron forced on the right?
Give me a hint
Compare line separation with distance and reverse the force for negative charge.
Compare my reasoning
- Radial rays spread apart with distance.
- The field is not uniform merely because the angles match.
- Rightward field gives a leftward electron force.
No uniform field is implied; the electron's force is leftward toward the positive source.
Look for these in your work
- Separate angular symmetry from uniformity.
- Distinguish field and electron force.
Common mistakes
- Positive outward; negative inward.
- Radial symmetry is not uniform strength.
- The actual negative particle's force opposes the field.
What can you explain now?
Which way do field arrows point around a positive point charge?
Compare with the explanation
Radially outward.
A positive test charge is repelled from the positive source.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Draw radial point-source fields and infer local forces without claiming uniform strength or calibrated ray counts.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.