A-LevelPhysicsElectric fields9702/12 · Oct/Nov 2019 · Q101 Mark
A positively charged oil droplet falls in air in a uniform electric field that is vertically upwards. The droplet has a constant terminal speed v₀ and the electric field strength is E. The magnitude of the force due to air resistance acting on the droplet is proportional to the speed of the droplet. Which graph shows the variation with E of v₀?
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
AGraph of v₀ against E, showing a straight line with negative gradient.
BGraph of v₀ against E, showing a curve with negative gradient that approaches the E-axis asymptotically.
CGraph of v₀ against E, showing a curve with positive gradient that approaches a constant v₀ value asymptotically.
DGraph of v₀ against E, showing a horizontal line (v₀ is constant).
✓ Correct answer
A: Graph of v₀ against E, showing a straight line with negative gradient.
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