What happens to the capacitance in variable capacitors when the plates separate?

Capacitance is defined by the formula ( C = \frac{\varepsilon A}{d} ), where ( C ) is capacitance, ( \varepsilon ) represents the permittivity of the dielectric material between the plates, ( A ) is the area of one of the plates, and ( d ) is the distance between the plates.

When the plates of a variable capacitor are separated, the distance ( d ) increases. According to the formula, as the distance ( d ) increases, the capacitance ( C ) decreases because the area ( A ) remains constant and the permittivity ( \varepsilon ) of the dielectric does not change. This relationship shows that the larger the distance between the plates, the lower the capacitance.

This decrease in capacitance due to increased plate separation is a fundamental principle of how capacitors work and is crucial in applications where variable capacitance is needed, such as tuning circuits.