Which type of capacitor changes its capacitance by altering the area of its plates?

Which type of capacitor changes its capacitance by altering the area of its plates?

• A. Counter EMF
• B. Open Capacitors
• C. Transformer Theory of Operation
• D. Variable Capacitors

Answer: (D)

Capacitance depends on the overlapping plate area: C = εA/d. With the dielectric and plate separation fixed, increasing the area A increases the capacitance proportionally. A variable capacitor is designed to change this effective plate area or overlap, typically by rotating or sliding plates to expose more or less area, thus tuning the capacitance. The other options describe concepts not about changing plate area to adjust C (counter EMF relates to back EMF in inductive devices, open capacitors isn’t a standard term, and transformer theory explains transformers). So, the device that changes capacitance by altering plate area is a variable capacitor.

Capacitance depends on the overlapping plate area: C = εA/d. With the dielectric and plate separation fixed, increasing the area A increases the capacitance proportionally. A variable capacitor is designed to change this effective plate area or overlap, typically by rotating or sliding plates to expose more or less area, thus tuning the capacitance. The other options describe concepts not about changing plate area to adjust C (counter EMF relates to back EMF in inductive devices, open capacitors isn’t a standard term, and transformer theory explains transformers). So, the device that changes capacitance by altering plate area is a variable capacitor.