Capacitors

Question 1

What is a capacitor

Answer 1

Two conductive plates (e.g. metal) separated by an insulator (e.g. air)

Question 2

Exponential decay equation

Answer 2

Q=Qoe^-t/RC
Q is charge (C)
Qo is initial charge (C)
e is exponential
t is time in seconds
R is resistance of the capacitor (ohms)
C is capacitance (F)

Question 3

Time constant equation

Answer 3

t=RC
t is time in seconds
R is resistance in ohms
C is capacitance (F)

Question 4

For discharging what % of original value will time constant be at

Answer 4

37%

Question 5

For charging what % of maximum value will time constant be at

Answer 5

63%

Question 6

Capacitive reactance

Answer 6

Impact of the capacitance on the flow of current.

Question 7

Capacitive reactance equation

Answer 7

Xc = V/I
Xc is capacitive reactance in ohms
V is voltage (V)
I is current (A)

Question 8

Why can’t we use normal V=IR equation when dealing with capacitor?

Answer 8

Wrong Physics, we get 0 marks

Question 9

What can capacitors in AC circuit act as?
And why?

Answer 9

High pass filters.
Since capacitor passes high frequency A.C. much better than low frequencies or d.c. means it can be used to pass high frequency electrical signals but blocks low frequency

Question 10

What should we always be careful to do when reading time constant graph?

Answer 10

See unit for x axis as will often be in ms as opposed to s