What is a capacitor?
A component that stores an electric charge and often consists of two foil plates separated by an insulating layer.
What is the symbol for capacitance?
C
What happens when a source of e.m.f. is connected to a capacitor?
Electrons flow from the negative terminal to one of the plates, creating a charge imbalance.
What is the unit of capacitance?
Farads (F)
What are practical capacitors usually measured in?
Micro-farads (μF) or nano-farads (nF)
How many micro-farads are in one farad?
1 F = 1,000,000 μF
How many nano-farads are in one farad?
1 F = 1,000,000,000 nF
What type of capacitor uses a ceramic material as the insulating layer?
Ceramic capacitor
What is an electrolytic capacitor?
A capacitor that uses an electrolytic paste as the insulating layer and must have its negative lead connected to the negative of the supply.
What is the relationship between charge and potential difference across a capacitor?
The charge stored is directly proportional to the potential difference.
What is the formula relating charge (Q), capacitance (C), and potential difference (V)?
Q = C * V
What does the area under the charge/potential difference graph represent?
The energy stored on a capacitor.
What is the formula for energy stored (E) on a capacitor?
E = 1/2 * Q * V
What is the maximum initial current when charging a capacitor?
I_max = supply voltage / resistance (R)
What is the maximum initial current when discharging a capacitor?
I_max = potential difference across the capacitor / resistance (R)
What happens to the current when a capacitor is fully charged?
Current ceases to flow.
What is the effect of increased capacitance on charging time?
The greater the capacitance, the longer it takes to charge.
What is the effect of increased resistance on charging time?
The greater the resistance, the longer it takes to charge.
What is a trimmer capacitor?
A very small capacitor used for making fine adjustments in circuits.
What is the formula for work done (W) in relation to charge and potential difference?
W = Q * V
What does the term ‘fully charged’ mean for a capacitor?
When the potential difference across the capacitor equals the e.m.f. of the cell.
What is the relationship between charge (Q) and capacitance (C) in terms of potential difference (V)?
C = Q / V
What is the significance of the gradient of the charge vs. potential difference graph?
It represents the capacitance of the capacitor.
What happens to the charge on a capacitor when it discharges?
The charge flows off the negative plate, reducing the potential difference to zero.
