9702 · 18.3
Electric force between point charges flashcards
Revision flashcards for Cambridge 9702 Electric force between point charges (syllabus 18.3). Flip, recall, then mark a real past-paper question.
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What fundamental law describes the electrostatic force between two point charges?
Coulomb's Law.
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How does the electrostatic force between two point charges depend on their separation distance?
It is inversely proportional to the square of their separation distance ($F \propto 1/r^2$). This is an inverse square law.
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State the complete formula for the electrostatic force between two point charges.
$F = \frac{1}{4\pi\epsilon_0} \frac{Q_1Q_2}{r^2}$
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Under what condition is the electrostatic force between two point charges attractive?
When the charges have opposite signs (one positive, one negative).
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What does the constant $\epsilon_0$ represent in Coulomb's Law?
The permittivity of free space.
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What is the nature of the force between two negative charges?
Repulsive.
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What is the approximate value of the permittivity of free space, $\epsilon_0$?
\$8.85 \times 10^{-12} \text{ F m}^{-1}$.
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How does the force change if the distance between two charges is halved?
The force becomes four times stronger (due to the inverse square relationship).
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For charged spheres, where is the charge considered to be concentrated for Coulomb's Law calculations?
At their geometric center.
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What is the direction of the electrostatic force between two point charges?
Along the straight line connecting their centers.