The plates on a vacuum capacitor have a radius of 2 point 5 millimeters and are separated by a distance of 0 point 7 5 millimeters What is the capacitance of this capacitor?

For a vacuum parallel-plate capacitor, use C = ε₀A/d, where A = πr². With r = 2.5 × 10⁻³ m and d = 0.75 × 10⁻³ m, the area is about 1.96 × 10⁻⁵ m², giving C ≈ (8.85 × 10⁻¹²)(1.96 × 10⁻⁵)/(0.75 × 10⁻³) = 2.3 × 10⁻¹³ F. So the capacitance is 2.3 × 10⁻¹³ F, choice A.

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