Intelligent assessment and revision tools for OCR A Physics

Two parallel horizontal conducting plates are separated by a distance d in a vacuum. A constant potential difference V is applied across the plates, creating a uniform electric field. A small sphere with a fixed positive charge is held stationary between the plates and experiences an electrostatic force F. If the potential difference is doubled and the plate separation is halved, what is the new electrostatic force experienced by the sphere?

• A It remains at F because the two changes cancel each other out.
• B It increases to 2F because the force is only proportional to the potential difference.
• C It increases to 4F because the field strength is proportional to potential difference and inversely proportional to plate separation.
• D It decreases to 0.5F because halving the distance reduces the strength of the field at that point.