Capacitance And Capacitors Flashcards
A capacitor is fully charged after 25 seconds to a battery voltage of 20 Volts. The battery is replaced with a short circuit. What will be the voltage across the capacitor after one time constant?
7.36 volts
The voltage rating of a capacitor is?
the max voltage that can be constantly applied.
The relative permittivity of a capacitor is?
the relative permittivity of the dielectric in relation to a vacuum.
When checking a capacitor with an ohmmeter, if the reading shows charging but the final reading is less than normal then the possible fault is?
leaking dielectric capacitor.
Three capacitors 10 microfarads, 10 nanofarads and 10 millifarads are connected in parallel. What is the total capacitance?
10.01001 millifarads.
If a 1 milliFarad capacitor has a potential difference across it of 5V, what is the energy stored?
12.5 milliJoules.
A capacitor with double the area and double the dielectric thickness will have?
the same capacitance.
An electrolytic capacitor is used where?
there is a polarized input.
What must you do to make a 3 F capacitor circuit into a 2 F circuit?
Put a 6 F capacitor in series.
The time required to fully charge a 1 µ(micro)F capacitor in series with a 100k ohm resistor is?
500 milliseconds.
A 50 μ(micro) Farad capacitor is fed with a current of 25 milliAmpere. How long will it take to charge it to 100Volts?
1 second.
In a circuit C = 25 microfarads and the current flow is 40 microamps for 4 seconds. What is the voltage?
6.4Volts.
Three 12 µ(micro)F capacitors are in series. The total capacitance is?
4 µ(micro)F.
The time constant of a capacitor is the time?
for the emf to reach 63.2% of maximum.
The amount of electricity a capacitor can store is directly proportional to the?
plate area and inversely proportional to the distance between the plates.
The capacitance of a capacitor is dependant upon?
the type of material separating the plates.
When different rated capacitors are connected in parallel in a circuit, the total capacitance is?
equal to the sum of all the capacitances.
One Picofarad is?
1 * 10-12 farad.
The switch on a DC circuit containing a fully charged capacitor is opened. The voltage across the capacitor?
remains equal to the original charging voltage supply.
The current in a DC circuit containing a fully charged capacitor is?
zero.
A capacitor is a barrier to?
D.C.
What is the total capacitance of a parallel circuit containing three capacitors with capacitance of 0.25microfarad, 0.03microfarad, and 0.12microfarad, respectively?
0.4 µ(micro)F.
When two capacitors are connected in series?
the charge stored on each is the same.
The charge on a capacitor is expressed as?
the product C * V.
When handling a high voltage capacitor in an electrical circuit, be sure it?
is fully discharged before removing it from the circuit.
The dielectric constant of a capacitor is a measurement of?
the electrostatic energy storing capacity of the capacitor dielectric.
Three 12 microfarad capacitors in parallel. The overall circuit capacitance is?
36 microfarads.
A circuit has 1 megohm and 8 microfarads. What is the time constant?
8 seconds.
A capacitor rating is?
the maximum continuous voltage it can take.
The multiplier colour coding on a capacitor is in?
picofarads.
The total capacitance of the circuit shown is?
4µ(micro)F.
When a capacitor is charged from a DC supply, the voltage/time curve is?
exponential.
An electrolytic capacitor is used because it has a?
small physical size for a large capacity.
An electrolytic capacitor would be used in circuits supplying?
heavy / light loads.
What is the correct description of Option C?
small physical size for a large capacity.
In what type of circuits would an electrolytic capacitor be used?
heavy / light loads.
How long does a 20 Picofarad capacitor with a 1 Megohm resistor take to charge?
100 microseconds.
Time constant (TC) = RC = 20/1,000,000,000,000 * 1,000,000 = 20/1,000,000 = 20 microseconds. But fully charged is 5 * TC = 100 microseconds.
What is the discharge curve of a capacitor?
Exponential.
What is the value of a monolithic capacitor with 103 on it?
10,000pf.
103 means 10 followed by 3 zeros. Capacitors are always measured in picofarads.
What is the formula for working out the capacitance of a capacitor?
c = K*A/d.
What is the total capacitance of 3 capacitors each 12milliFarad in a parallel circuit?
36milliFarad.
What is the time constant of a combination of 1 megohm and 8 microfarad?
8 seconds.
1,000,000 * 8/1,000,000 = 8 seconds. Note: Time Constant is asked for, not ‘time to charge’.
What is the voltage across a fully charged capacitor?
Same as circuit voltage.
Normal theory is that a fully charged capacitor has an equal (and opposite) voltage to the supply. However, a capacitor is never fully charged (something in the order of 99.999999% charged).
When would you use an electrolytic capacitor?
Large output compared to size required.
What is the value of a capacitor with Brown, Black and Orange bands?
10 nanofarads.
Brown = 1, Black = 0, Orange = x1000. Total is 10,000 picofarads (always picofarads with capacitors) = 10 nanofarads.
What will the voltage measured between the plates of a capacitor generally be?
the same as applied voltage.
What is the dielectric constant of a capacitor?
electrostatic storing capability of the dielectric.
What is one microfarad in farads?
1 * 10-6 farads.
What would be the charge of a capacitor with 6 volts and 2400 pico-coulombs if the voltage was 1.5 volts?
600 * 10-12 coulombs.
Q = CV, so direct relationship of charge to voltage. 1.5V is 1/4 of 6V, so charge is 1/4 of 2400 picocoulombs.
How is the dielectric strength of a capacitor measured?
Farads per meter.
What is the total capacitance of three capacitors connected in series, each having a value of 12 picofarads?
4 picofarads.
12/3 = 4.
