Capacitance

Question 1

What are the differences between Ceramic and Electrolytic capacitors?

Answer 1

Ceramic capacitors have no polarity but Electrolytic capacitors must be connected the right way round or they will literally explode. Larger capacitances (greater than 1μF) will generally be Electrolytic.

Question 2

Why does a circuit with only a capacitor and a battery show a small spike in current when the circuit is switched on?

Answer 2

This is the electrons moving from the positive plate to the negative plate, creating a pd across the plates. It happens very quickly so the current can be relatively large.

Question 3

What are capacitors used for?

Answer 3

They are used to store charge (in the form of charge differnce between the plates).

Question 4

Define the capacitance of a capacitor.

Answer 4

The capacitance of a capacitor is defined as the ratio of charge stored (Q) to potential difference (V) across the capacitance
(C=Q/V)

Question 5

Give an equation which describes the discharge of a capacitor.

Answer 5

Q=Qo(e^-t/CR)

Question 6

From the equation Q=Qo(e^-t/CR) which other equations can we derive?

Answer 6

V=Vo(e^-t/CR), I=Io(e^-t/CR) and I=Vo/R(e^-t/CR)

Question 7

How do we define the time constant τ of a capacitance discharge circuit?

Answer 7

The time constant τ is equal to the time taken for the charge on the capacitor to fall to 37% of its initial value.

Question 8

What is the energy stored by a capacitor?

Answer 8

E = (QoVo)/2 or (C(Vo)^2)/2 or (Qo)^2/2C

Question 9

What are the two families of Capacitor?

Answer 9

Ceramic and Electrolytic.