(7.4) - Capacitance

Question 1

What is Capacitance?

Answer 1

Measure of how much charge a capacitor can store

Question 2

What is relative permittivity / dielectric constant?

Answer 2

Measure of how much the dielectric material increases the capacitance compared to air

Question 3

Describe the action of a simple polar molecule that rotates in the presence of an electric field.

Answer 3

• A simple polar molecule is a molecule which has a charge on either end of it
• This molecule, when in the presense of a capacitor which is connected to a battery, feels two simul pulls
• The molecule experiences a torque, and its negative side aligns with positive place and vice versa

Question 4

The area under a charge-voltage graph equals?

Answer 4

Energy stored in a capacitor

Question 5

Charging of Capacitors

What does a Current-time graph look like?

Answer 5

Exponential decay (Rate of decrease decreases)

Question 6

Charging of Capacitors

What does a Voltage-time and Charge-time graph look like?

Answer 6

Increases at a decreasingly exponential rate (Increases fast but slows down over time)

Question 7

Discharging of Capacitors

What does a Current-time, Voltage-time and Charge-time graph look like?

Answer 7

Exponential decay (Rate of decrease decreases)

Question 8

What is the area of current-time graph?

Answer 8

Charge stored for a certain time interval

Question 9

What is the gradient of charge-time graph?

Answer 9

Current at that time

Question 10

For DISCHARGING, what is time constant of a capacitor?

Answer 10

The time taken for the charge to fall to 1/e of its initial value.

Question 11

For CHARGING, what is time constant of a capacitor?

Answer 11

The time taken for the charge to rise to (1 - 1/e) of its maximum value.

Question 12

The time it takes for the charge or voltage across a discharging capacitor to halve is given by what equation?

Answer 12

0.69(RC) (or 0.69(𝜏))