1. Concept: Introducing an insulating dielectric material between capacitor plates reduces the internal electric field via polarization, which fundamentally acts to multiply and increase the total capacitance.
2. Formula: $$ C_{med} = \epsilon_r C_{vac} $$
3. Solution: - Original vacuum capacitance: \( C_{vac} = 20 \mu\text{F} \).
- Dielectric constant of new slab: \( \epsilon_r = 2 \).
- Calculate new capacitance: \( C_{med} = 2 \times 20 \mu\text{F} = 40 \mu\text{F} \).
- Because 40 is twice the original 20, the capacitance has precisely doubled.
4. Why other options are incorrect: Option D occurs if you erroneously divide by the dielectric constant (which happens to field strength, not capacitance). Option B is a distractor for square-law calculations.
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