Capacitors 4

1. A capacitor is rated 12V 60µF.
1.1. Calculate the charge on the fully charged capacitor.

1.2. State one way in which a capacitor is similar to a battery.
produces electrical energy

1.3. State one way in which a capacitor is different from a battery.
does not use a chemical process

2. The area of each plate of a capacitor is 0,05m2. The air gap between the plates is 4mm.
2.1. What is the permittivity of free space?
8,85 x 10-12F.m-1

2.2. Calculate the capacitance of this capacitor.

2.3. This capacitor is now connected to a 200V DC source.

2.3.1. Calculate the charge that accumulates on each plate.

2.3.2. Which parts of a capacitor are considered “physical designs?”
A (area of plates) and d (distance between plates)

2.3.3. How can the amount of charge stored on each plate be increased without altering the physical design of the capacitor.
increase voltage of battery

2.4. Assume that the capacitor is now fully charged. The battery is removed and replaced with a bulb.

2.4.1. Will the bulb remain glowing for an extended period of time? Explain.
No. Capacitor will quickly discharge.

2.4.2. In which direction will the current flow compared to the current direction when the battery was operational.

3. The charge on one capacitor plate is 8 x 10-10C and the voltage across the plates is 200V.

3.1. What is the charge on the other plate?
-8 x 10-10C

3.2. What s the net charge of the plates?

3.3. Calculate the capacitance of the capacitor.

3.4. If the area of a plate is 50cm2, calculate the distance between the plates.

4. To maximise the capacitance of a capacitor, state whether each of the following must be maximised or minimised.

4.1. area of the plates

4.2. dielectric permittivity

4.3. separation distance of plates

5. Study the following graphs

5.1. Which graph shows capacitance against plate area?
Graph A

5.2. Which graph shows capacitance against plate separation?
Graph D

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