Gravitational and Electric Fields and Potentials
Comparing inverse-square gravitational and electric fields, field strength, potential, potential energy, uniform fields and orbital applications.
How to study A-level Physics
Define the system, represent the physics, select a justified model, calculate transparently, then test the result against units, limits and evidence.
Core concepts
Concept 1
Field strength is force per unit test quantity, while potential is potential energy per unit test quantity.
Exam cue: Keep field, force, potential and potential energy as distinct quantities.
Concept 2
Point or spherical sources produce inverse-square fields and inverse-distance potentials under the model.
Exam cue: Use a sign convention and reference zero appropriate to the field model.
Concept 3
Gravitational interactions between masses are attractive; electric interactions may attract or repel according to charge.
Exam cue: For orbits, identify gravity as the resultant providing centripetal acceleration.
Risk pitfalls and guardrails
Using an inverse-square relationship for potential.
Guardrail: Do not substitute a memorised formula until you have identified the system, variables, direction, assumptions and valid range of the model.
Dropping the sign of electric charge or gravitational potential.
Guardrail: Do not substitute a memorised formula until you have identified the system, variables, direction, assumptions and valid range of the model.
Assuming zero potential means zero field everywhere.
Guardrail: Do not substitute a memorised formula until you have identified the system, variables, direction, assumptions and valid range of the model.
Memory anchors
Field Strength
Field strength is force per unit test mass or positive test charge.
Potential
Potential is potential energy per unit test mass or charge.
Inverse Square
Point-source field strength varies as one over distance squared.
Point Potential
Point-source potential varies as one over distance.
Equipotential
No work is done moving a test object along an equipotential surface.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
What is gravitational field strength at a point?
A 3.0 kg mass experiences a 24 N gravitational force. What is the local field strength?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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