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In this lesson, we will learn how to calculate the capacitance of two parallel charged plates given their surface area and the distance between them.

Q1:

An air-filled (empty) parallel-plate capacitor is made from two square plates that are 25 cm on each side and 1.0 mm apart. The capacitor is connected to a 50-V battery and fully charged. It is then disconnected from the battery and its plates are pulled apart to a separation of 2.00 mm.

What is the capacitance of this new capacitor?

What is the charge on each plate?

What is the electrical field between the plates?

Q2:

A capacitor is made from two flat parallel plates placed 1.9 mm apart. When a charge of 0.040 µC is placed on the plates, the potential difference between them is 360 V.

What is the capacitance of the plates?

What is the area of each plate?

What is the charge on the plates when the potential difference between them is 850 V?

What is the maximum potential difference that can be applied between the plates so that the magnitude of electric fields between the plates does not exceed 4.5 MV/m?

Q3:

An empty parallel plate capacitor has a capacitance of 80 µF. How much charge must leak off its plates before the voltage across them is reduced by 250 V?

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