Unit 4: Capacitance

Question 1

What is capacitance(C) and derive an equation from said definition

Answer 1

The charge(Q) stored per unit voltage(V)

C = Q/V

Question 2

Give the equations for energy stored in a capacitor

Answer 2

E = 1/2(QV) = 1/2(CV^2) = 1/2(Q^2/C)

Question 3

How does one find energy stored from a charge against pd graph

Answer 3

Area under the graph

Question 4

What is the time constant (RC)

Answer 4

This determines how long it takes a capacitor to charge or discharge

Question 5

Charge falls to what percentage of its initial value after 1 time constant

Answer 5

37%

Question 6

After how many time constants is a capacitor considered to be fully discharged

Answer 6

5

Question 7

What is the equation giving the charge on a discharging capacitor

Answer 7

Q = Q0*e^(-t/RC)

where Q0 = initial charge

Question 8

How can one find time constant from a graph

Answer 8

Find where charge = 37% on the y-axis ( charge axis ) and find the corresponding x-axis ( time ) value

Question 9

How would the graph change using voltage or current as the y-axis

Answer 9

it would remain the same

Question 10

How would the graph change for charging a capacitor

Answer 10

Flipped in the x-axis