Section 10 - Capacitors

Question 1

What is a capacitor

Answer 1

A capacitor is an electrical component made up of two conducting plates separated by a gap or a dielectric

Question 2

How a capacitor works

Answer 2

When a capacitor is connected to a power source, positive and negative charges build up on opposite plates, creating a uniform electric field between them

Question 3

Capacitance def

Answer 3

The amount of charge per unit potential difference stored by a capacitor

Question 4

Capacitance f

Answer 4

C = Q/V

Question 5

Capacitance units

Answer 5

C/V or F (farads)

Question 6

Permittivity def

Answer 6

A measure of how difficult it is to generate an electric field in a certain material

Question 7

Relative permittivity def

Answer 7

The ratio of the permittivity of a material to the permittivity of free space, may also be referred to as dielectric constant

Question 8

How a dielectric works - No charge is applied

Answer 8

• Dielectric is made up op polar molicules that have a positive and a negative charge
• When no charge is applied, there is no electric filed, so the polar molecules point in random directions

Question 9

How a dielectric works - Charge is applied

Answer 9

• When a charge is applied, an electric field is generated
• Negative ends of polar molecules attract to the positively charged side and vice versa
• This causes all molecules to rotate and align themselves with the electric field
• The molecules have their own electric field which now opposes the applied electric field of the capacitor. The large the permittivity, the larger this electric field is
• This reduces the overall electric field, which reduces the potential difference needed to charge the capacitor - so the capacitance increases

Question 10

Capacitance, relative permittivity

Answer 10

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Question 11

2 formulae for energy stored on a capacitor

Answer 11

E = 0.5QV
E = 0.5CV^2

Question 12

What factors does time taken to charge and discharge a capacitor depend on

Answer 12

Capacitance
Resistance of the circuit

Question 13

3 formulae for charging a capacitor

Answer 13

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Question 14

3 formule for discharging a capacitor

Answer 14

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Question 15

3 graphs for capacitor charging

Answer 15

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Question 16

3 graphs for capacitor discharging

Answer 16

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Question 17

Time constant f

Answer 17

RC

Question 18

When t = Q/Qo

Answer 18

t = 1/e, Q is 0.37 of Qo

Question 19

Time constant def

Answer 19

The time taken for the charge, potential difference or current of a discharging capacitor to fall to 37% of its value when fully charged

Question 20

The larger the resistance in series with the capacitor, the ______ it takes to __________________

Answer 20

1) longer
2) Charge or Discharge

Question 21

Approximate time taken for a capacitor to charge or discharge

Answer 21

5*time constant = 5RC

Question 22

Finding the time constant from a log-linear graph

Answer 22

Blank or insert pic

Question 23

Time to halve for a capacitor

Answer 23

0.69* time constant = 0.69RC