Lesson 4: Understanding Capacitance and How it Affects a Circuit

One picofarad in decimal form is written as ? F.

.000000000001 (11 zeros, 12 total spaces behind the decimal

One microfarad in decimal form is ? and may be abbreviated ?

0.000001 F / 1 µF

One picofarad is one farad times ?

10x^−12

What is the physical structure of a capacitor?

2 metallic plates separated by a dielectric

How many time constants are required to charge a capacitor to a level where it is considered to be fully charged?

5

How many time constants for a capacitor to fully discharge?

5

A time constant is the amount of time required to charge a capacitor to ? of the amount left to reach its full charge.

63.2%

? is the letter designation for capacitance.

C

A(n) ? will not hold its charge indefinitely.

Capacitor

Current can flow only during the period of time that a capacitor is ? .

Charging or discharging

When a capacitor of one farad is connected to a source of one volt, its charge is one ? .

Coulomb ( 1 Amp )

If a capacitor is subjected to a voltage in excess of that for which it is designed, the electron flow may puncture the insulation, causing an arc-through, which destroys the ? and, therefore, the capacitor.

Dielectric

The type of dielectric used has no effect on a capacitor.

False, the type of dielectric will determine the amount of capacitance a capacitor will have.

Electrons flow through a capacitor.

False. The electrons flow back and forth from either side of the capacitor hitting both sides which charges it, but does not allow current to flow through the plates. cannot flow becuase of the dielectric material.

What is the unit of capacitance and its abbreviation?

Farad, F

One farad ? a practical unit of capacitance.

Is not. one farad is super small. So we say micro farad

A capacitor has the same area of plates and the same distance between the plates. The capacitance will be ? if air is used instead of insulating oil.

Lower

When a capacitor is connected in a circuit with a resistor, the amount of time needed to charge the capacitor is determined by the ? .

RC time constant

A picofarad is also called a micromicrofarad and may be abbreviated µµF.

True

An AC ammeter indicates a steady current when it is connected in series with a capacitor across an AC source.

True

Would two conductors feeding a load have capacitance?

Yes

Select factors that determine the capacitance of a capacitor.

a. Area of the plates (conducting surfaces) b. Distance between the plates c. The type of dielectric used (insulating material)

The ? field is formed when electrons are removed from one plate and deposited on the other.

electrostatic

The term ? refers to the force holding an electrical charge across a capacitor's plates.

electrostatic

In a capacitive circuit, the current will ? the voltage by ? .

lead / 90°

When a DC voltage source is connected to a capacitor, electrons will be moved from the plate connected to the ? and deposited on the plate connected to the ? pole. This will continue until the voltage across the capacitor equals the voltage source.

positive / negative

Select the equation to find the time constant for a resistive-capacitive circuit.

t = R x C (t = Time, R = Resistance, C = Capacitance)

How long will it take for a 50 µF capacitor to fully charge if it is in a series circuit with a 100 KΩ resistor?

t = R x C, 100,000 x .00005 = 5 seconds. Multiply the seconds by 5 time constants to be fully charged. 5 x 5 = 25 full seconds.