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Electric fields
Study Electric fields as part of Fields and their consequences for AQA A-Level Physics 7408. This topic hub connects the approved learning objectives to flashcards, MCQs, exam-style questions, answer explanations, revision notes, key terms, common mistakes, exam tips, and mini practice tests where those assets are published. Use the overview to separate definitions, equations, data analysis, graph interpretation, practical reasoning, and conceptual explanations before moving into the practice tools. For Electric fields, pay close attention to units, assumptions, evidence and boundary distinctions so answers stay specific to the exact A-Level Physics context.
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10
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10
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90 min
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Coulomb's law4 objectives
- State and apply Coulomb's law.
- Explain inverse-square behaviour for point charges.
- Determine force direction for like and unlike charges.
- Compare Coulomb's law with Newton's law of gravitation.
Electric field strength4 objectives
- Define electric field strength as force per unit positive charge.
- Calculate electric field strength due to point charges.
- Calculate electric field strength between parallel plates.
- Interpret electric field-line diagrams.
Electric potential4 objectives
- Define electric potential in an electric field.
- Calculate work done moving charge through a potential difference.
- Link electric potential energy to charge and potential.
- Interpret electric potential graphs.
Key terms
Exam tips
- Apply Coulomb's law correctly: When calculating the force between two point charges, use the formula F = k q₁ q₂ / r². For example, if q₁ = 2 C, q₂ = 3 C and r = 0.5 m, then F = (8.99×10⁹ N·m²/C²) × (2 C × 3 C) / (0.5 m)² = (8.99×10⁹ × 6) / 0.25 = 5.394×10¹⁰ / 0.25 = 2.1576×10¹¹ N. The force is attractive if the charges are opposite, repulsive if they are the same. Always check that the distance is in metres and charges in coulombs.
- Understanding Inverse-Square Law: Remember that the force between two point charges decreases with the square of the distance between them. Use Coulomb's law to calculate the force accurately.
Common mistakes
- Misunderstanding Coulomb's Law: Remember that Coulomb's law states that the force (F) between two point charges (q1 and q2) is inversely proportional to the square of the distance (r) between them. The formula is F = k * |q1 * q2| / r^2. When applying this, substitute the values correctly to see how increasing distance decreases the force.
- Misunderstanding Inverse-Square Law: To fix this, remember that Coulomb's law states that the force (F) between two point charges (q1 and q2) is given by F = k * |q1 * q2| / r^2, where r is the distance between the charges. This means that as the distance increases, the force decreases by the square of that distance. Always apply the formula correctly and recognize that the force diminishes as the distance increases.
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