Two identical small metal spheres, P and Q, carry charges of +3.2 nC and -1.8 nC respectively. They are held in a vacuum with their centres separated by a distance of 5.0 cm.
Question
Calculate the magnitude of the electric force between the spheres. [2]
Hint
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Hint
Use Coulomb’s law: \(F = \frac{k|q_1q_2|}{r^2}\).
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\(F \approx 2.1 \times 10^{-5}\,N\)
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Question
State whether the force is attractive or repulsive. [1]
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Remember: Opposite charges attract while like charges repel.
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Attractive
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Question
Determine the charge on each sphere after they are touched together. [2]
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The total charge is redistributed equally between the two spheres.
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\(q = 0.7\,nC\)
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Question
Calculate the magnitude of the electric force between the spheres after they are touched and separated. [1]
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Now use Coulomb’s law with the new charge value \(q = 0.7\,nC\).
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\(F \approx 1.8 \times 10^{-6}\,N\)
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