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AQA · GCSE · Physics · Higher

Spark Potential Difference

Q04.4 4 marks

Figure 6 shows the negatively charged metal dome and an earthed conductor.

Figure 6
Figure 6

Figure 6

Enlarged question image

Figure 6

When the earthed conductor is moved towards the metal dome, there is a spark between the dome and the earthed conductor.

energy transferred = charge flow × potential difference, E=QVE = QV

The spark transfers 0.60 J of energy, and 2.0 μC of charge is transferred from the dome to the earthed conductor.

Calculate the potential difference between the metal dome and the earthed conductor.

Use the Physics Equations Sheet.

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Marking points

  1. 1 Converts 2.0 μC to 2.0 × 10^-6 C.
  2. 2 Uses E = QV with 0.60 J and the charge in coulombs.
  3. 3 Rearranges correctly for V.
  4. 4 Obtains 300 000 V, subject to official error-carried-forward guidance.

Full-mark answer

Q=2.0 μC=2.0×10−6 CQ=2.0\,\mu\text{C}=2.0\times10^{-6}\text{ C}. Using E=QVE=QV, \(V=E/Q=0.60/(2.0×10^{-6})=3.0×10^5text{ V}\).

Why this answer loses marks

I used the charge in microcoulombs directly in E = QV.

The equation needs charge in coulombs, so convert the prefixed unit before substituting and rearranging for potential difference.

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