Electric capacity of a flat capacitor:
С = ε * ε0 * S / D, ε is the relative permittivity of the dielectric, ε0 is the electrical constant, S is the area of the capacitor plates, D is the thickness of the dielectric (the distance between the plates).
Electric capacity before changing the distance between the plates:
C1 = ε * ε0 * S / D1.
Electric capacity after changing the distance between the plates:
C2 = ε * ε0 * S / D2.
From the initial conditions: D1 = 4D2.
C1 / C2 = (ε * ε0 * S / D1) / (ε * ε0 * S / 4D1) = 4.
Answer: The electrical capacity will increase by 4 times.
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