What changes have been made to the charging capacity of capacitors and bipolar voltage capacitors?

C = Q/U (definition)

Keep the power connection: u unchanged.

Disconnect the power supply: Q remains unchanged.

1. After charging, keep the power on (U unchanged) and double the area of the electrode plate (to 2S).

From C = εS/4πkd: c to 2C.

Then from C = Q/U, 2c = 2q/u.

That is, u remains unchanged and q doubles.

2. Disconnect the power supply after charging (Q remains unchanged), and then double the distance between the two plates (change it to 2d).

From C = εS/4πkd: c to C/2.

Then from C = Q/U, it is: C/2 = Q/2U.

That is, q remains the same and u doubles.

3. Turn off the power supply after charging (Q remains unchanged), and then halve the electrode area (to S/2).

From C = εS/4πkd: c to C/2.

Then from C = Q/U, it is: C/2 = Q/2U.

That is, q remains the same and u doubles.