# Physics, I don't understand what to do ?

The figure shows a variable “air gap” capacitor of the type used in manually tuned radios. Alternate plates are connected together; one group of plates is fixed in position, and the other group is capable of rotation. Consider a capacitor of n = 8 plates of alternating polarity, each plate having area A = 1.95 cm2 and separated from adjacent plates by distance d = 4.20 mm. What is the maximum capacitance of the device?

### 2 Answers

- KnrLv 42 months agoFavorite Answer
Use the formula C = (n-1) e0A /d, and substituting the given values get your answer.

- Login to reply the answers

- skeptikLv 72 months ago
Use the formula for parallel-plate capacitance, with the area of the plates in the formula being the sum of that of each individual plate. Bear in mind that for any plate that is between two opposite plates, you take the area of both sides. The plates on the ends will only count once.

Which means that according to your diagram, each pole will be connected to an equivalent plate with seven times the area of one plate, and the capacitance will be at a maximum when the plates are rotated into the fully-meshed position.

- Login to reply the answers