3.9 Capacitors Flashcards
A charged capacitor is said to?
Block DC current flow.
What is the unit for capacitance?
the Farad = F
The capacitor is said to pass?
Pass AC
A charge of one coulomb exists on a capacitor when?
6.25 x 10 to the powe of 18 electrons are moved from one plate to the other.
What factors effect a capacitor area of the capacitor plate
What factors effect a capacitor?
Area of the capacitor plates, Distance between the capacitor plates, Dielectric material between the capacitor plates.
What happens when the total area of the plates increases?
Capacitance increases, the greater area can hold a greater charge.
What happens to the capacitance if the plate area is decreased?
Capacitance decreases
How else can you increase the surface area of capacitor plates?
By layering the plates using both sides.
What happens to the capacitance if the plate distance between them is altered?
Closer they are = more capacitance, further they are apart = less capacitance
What is the purpose of the diaelectric material.
Transmitting the electric force from one plate to the other. it is a good support of electrostatic fields.
Define diaelectric constant,
Defines the ability of the material to improve the capacity of the capacitor
An increase in plate are and the diaelectric constant will result in?
Increase in capacitcance.
If the diaelectric material is increased but the plates stay the same what happens?
the distance between the plates increase but the plate material doesn’t causing a capacitance decrease.
Define working voltage
Working voltage is the maximum DC voltage that can be applied to a capacitor before the dieelectric material is damaged causing the capacitor to be U/S
To increase the working voltage of the capacitor what can be done?
The diaelectric material can be replaced for one of a greater strength or increase the diaelectric thickness.
Working voltage is written?
On the body of the capacitor
What value of the capacitor is effected by the diaelectric strength?
the potential difference, or Working voltage
What does the diaelectric strength of a capacitor refer to?
Potential difference required to make a spark jump.
What does diaelectric constant of a capacitor refer to?
Determines the amount of energy that a capacitor can store when voltage is applied.
How does a trimmer capacitor change the values?
By a screw which compressed or decompresses the internal plates/
Which capacitor type is polarity concious?
Electrolytic capacitor, must have a DC potential applied to it. (Tantalum capacitor)
Most capacitors are named after what?
The diaelectric material inside the capacitor, EG: Ceramic capactiro has a ceramic diaelectric.
what are the 2 groups of capacitors?
Fixed and Variable.
Describe the layout of the colour code for capacitors
Top colour = 1st digit in uF, 2nd colour down = 2nd digit uF, Dot = Multiplier, bottom colour = Voltage
What is the diaelectric in a variable capacitor
mica
How many time constants does it take to reach 100% charge of a capacitor?
5 TC
How many time constants does it take to reach 0V on discharge?
5 Time constants
When charging a capacitor to 10V what is the voltage after 1 TC
6.32V (63.2% of 10V)
When discharging a capacitor what is the Voltage after 1 TC?
3.68V (Minus 63.2%)
How is the time constant for a capacitor calculated?
TC= R x C
What happens to capacitance in series and parallel?
Capacitcance diminishes in series and add’s in parallel
What are the signs of a good capacitor?
Resistance starts low and gradually increases.
