Capacitors

Question 1

What does a capacitor do

Answer 1

Store electrical charge

Question 2

What does the charge of a capacitor dependant on

Answer 2

The p.d across the capacitor
Q is directly proportional to V

Q = CV

C = Q/V

Question 3

What is capacitance?

Answer 3

The amount of charge stored per unit p.d

Question 4

Unit for capacitance

Answer 4

F (farad)

Question 5

Charging a capacitor

Answer 5

Electrons will flown from the negative terminal of the cell to the negative plate of the capacitor

The excess electron on the negative plate are going to repel electrons off the positive plate of the capacitor, which will move them towards the positive terminal of the cell

Overall the plates will have a equal and opposite charge

Question 7

How to add capacitors in parallel

Answer 7

Ct = C1 + C2 + C3

The voltage across each branch is the same
The charge is shared as the current is shared

Question 8

How to add capacitors in series

Answer 8

1/Ct = 1/C1 + 1/C2 + 1/C3

The voltage is shared to each branch
The charge is the same as the current each capacitor experiences is the same

Question 10

What is a capacitor made of?

Answer 10

Two plates of conducting material separated by an insulator, called a dialect

Question 11

What is a dialect and what can it be made from

Answer 11

The centre insulator of a capacitor

Air, ceramic, paper or mica

Question 12

What is the charge of a capacitor

Answer 12

Initially it is neutral with an even distribution of charges

When charging, the charges on a capacitor become separate, such that the plate become positively charged and one plate becomes negatively changed. It still has a net change of zero, but the charges have been redistributed and separated into positive and negative

Question 13

How do the charges on a capacitor become separate when charging

Answer 13

The charge is attracted of one plate by the positive terminal and repelled by the negative terminal on the opposite plate.

Question 14

When will the capacitor stop charging?

Answer 14

When there is no potential difference across the circuit. The voltage is equal to the cell or battery - the EMF is equal to the capacitance

Question 15

What 3 factors affect how much charge can be stored for a given p.d

Answer 15

The distance between plates (spacing)
- If you move them closer together more charge can be stored as the positive plate has a greater ability to attract negative charge to the opposite plate

The surface area by with the plates are overlapping
- The more they overlap, the greater ability the positive plate has to attract negative charge to the opposite plate

Dialectic permittivity
- The permativity of the material changes how much charge can be stored - the greater the permittivity, the more charge can be stored and the higher the capacitance
- Permittivity is a measure of the capacity of the capability of the substance to polarise and permit and electric field

Question 17

What is permittivity

Answer 17

Permittivity is a measure of the capacity of the capability of the substance to polarise and permit and electric field

Question 18

Uses of capacitors

Answer 18

(Can store charge for later use and release it quickly, generating a high output power)
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