Capacitors Flashcards
What are capacitors?
Devices that oppose a change in voltage
What is dielectric?
Insulating material between the two plates of a capacitor
What is capacitance?
The measure of the ability of a capacitor to store electric charge
What is the unit of capacitance measured in?
Farads (F)
What are three factors that determine the capacitance of a capacitor?
- Surface area of plates, the greater the surface, the greater the capacitance
- The distance between the plates. The closer the plates, the higher the capacitance
- The type of dielectric used
What is leakage current?
Current flow through the dielectric. It will eventually cause the capacitor to discharge
What is a leaky capacitor?
When the dielectric becomes weak and allows current to flow between the plates
What is electrostatic charge?
Refers to an electric charge that is stationary
What is dielectric stress?
Changing shape or stretching of the atoms in the dielectric due to the electrostatic field
What happens when you connect capacitors in series?
It has the same effect as increasing the distance between the plates, thus reduces the total capacitance
How are capacitance in series added?
Adds by product/sum or reciprocal method
What happens when you connect capacitors in parallel
Connecting capacitors in parallel has the same effect as increasing the plate area
How are values of capacitance added in parallel?
They are added directly
How do capacitors charge and discharge?
At an exponential rate
What is the RC time constant?
the amount of time required to charge
What is the formula for the RC time constant?
T=R*C
T=time
R=resistance
C=capacitance
What are applications for capacitors?
- Power Factor Correction
2 .Start windings in single phase motors - Phase shifts in electronic circuits
- Control for current circuits
- Control Frequency and pulse generation
What leads what in a capacitive circuit?
Current(I) leads Voltage(E) by 90 degrees in a purely capacitive circuit
What are capacitive reactances?
Opposition to current flow caused by a capacitor in an AC circuit
What happens when the polarity of the source voltage changes in a AC circuit?
The polarity of the charging capacitor changes
How much out of phase is the impressed voltage compared to the source voltage?
180 degrees out of phase
