Chapter 21 - Capacitance

Question 1

What is a capacitor?

Answer 1

Component that stores charge, consisting of two plates separated by an insulator (dielectric).

Question 2

Total capacitance if capacitors are in parallel

Answer 2

Total C = C1 + C2 + C3 + …

Question 3

Total capacitance if capacitors are in series

Answer 3

1/C = 1/C1 + 1/C2 + 1/C3 + …

Question 4

What is the area under a voltage-charge graph?

Answer 4

Energy stored in a capacitor.

Question 5

Exponential decay

Answer 5

Constant-ratio process in which a quantity decreases by the same factor in equal time intervals.

Question 6

What happens when a capacitor discharges?

Answer 6

Q decreases over time.
I and V also decrease as a result.
Eventually I, V and Q are zero.

Question 7

What is the equation for time constant?

Answer 7

Time constant = CR

Question 8

What is the value of I/V/Q when the time constant = CR?

Answer 8

e to the -1 i.e. 37% of the original value.

Question 9

Uses of capacitors

Answer 9

Release stored energy very fast.

Provide back up power to computers.
Emergency lighting.

Question 10

Smoothing capacitors

Answer 10

Rectifier circuit changes AC to DC.

Diode allows current in one direction only, and capacitor smooths it out.