Capacitance Of A Capacitor And Its Unit MDCAT Quiz with Answers

Capacitance is a measure of a capacitor’s ability to store charge per unit voltage. It is defined as the ratio of the charge stored on a capacitor to the potential difference (voltage) across its plates. Capacitance is a fundamental property that determines how much energy a capacitor can store for a given voltage.

Definition of Capacitance
The capacitance (
????
C) of a capacitor is defined by the formula:

ṃ
=
????
????
C=
V
Q
​
Where:

????
C is the capacitance (in farads, F),
????
Q is the charge stored on the capacitor (in coulombs, C),
????
V is the voltage drop (in volts, V).
This formula implies that the capacitance of a capacitor is directly proportional to the charge stored on its plates and inversely proportional to the potential difference between the plates.

Capacitance of a Parallel Plate Capacitor
For a parallel plate capacitor, the capacitance is given by:

????
=
????
????
????
C=ϵ
d
A
​
Where:

????
C is the capacitance (in farads, F),
????
ϵ is the permittivity of the dielectric material between the plates (in farads per meter, F/m),
????
A is the area of one of the plates (in square meters, m²),
????
d is the distance between the plates (in meters, m).
The capacitance increases as the area of the plates increases or the separation distance between the plates decreases. Furthermore, the material between the plates—the dielectric—also affects the capacitance. Materials with higher permittivity allow the capacitor to store more charge for a given voltage.

Unit of Capacitance
The SI unit for capacitance is the farad (F). One farad is defined to be the capacitance of a capacitor that stores one coulomb of charge when the potential difference between its plates is one volt. That is:

1
F
=
1
C
1
V
1F=
1V
1C
​
Where:

1
C
1C is one coulomb of charge,
1
V
1V is one volt of potential difference.
Since the capacitance values for most capacitors in practical applications are much smaller than 1 farad, capacitance is often expressed in subunits:

Microfarad (µF):
1
????
F
=
1
0
−
6
F
1μF=10
−6
F,
Nanofarad (nF):
1
nF
=
1
0
−
9
F
1nF=10
−9
F,
Picofarad (pF):
1
pF
=
“`
1
“`
0
−
12.
F
1pF=10
−12
F.
Capacitance and Dielectric Materials
The presence of a dielectric material between the plates of a capacitor increases its capacitance by a factor called the dielectric constant (
????
????
ϵ
r
​
). The capacitance with a dielectric is given by:

????
=
????
????
⋅
????
0
????
????
C=ϵ
r
​
⋅ϵ
0
​
d
A
​
Where:

????????℆
????
ϵ
r
​
is the relative permittivity (dielectric constant) of the material,
????
0
ϵ
0
​
is the permittivity of free space (
8.85
×
1
0
−
12
F/m
8.85×10
−12
f/m).
This shows that capacitors with high-dielectric constant materials can store more charge, which increases their capacitance.

Applications of Capacitance
Energy Storage: Capacitors store energy in the form of an electric field. The greater the capacitance, the greater the energy that can be stored by the capacitor for a given voltage.
Power Filtering: In power supply circuits, capacitors are used for the filtering and smoothing of voltage fluctuations by storing and releasing energy.
Timing Circuits: Together with resistors, capacitors are used in RC circuits to create timing and delay control.
Tuning: Variable capacitors are used in radio and communication equipment to tune circuits to different frequencies.
MDCAT Quiz: Capacitance of a Capacitor
The MDCAT Quiz on Capacitance typically contains questions about the calculation of capacitance of capacitors in various configurations, such as series and parallel, finding how dielectrics affect capacitance, and solving for energy stored in capacitors. Such questions are designed to test a student’s understanding of the interrelation among charge, voltage, and capacitance, and how this knowledge is applied in real life in electrical systems.

Free Flashcards for Capacitance
Free flashcards for capacitance would help students fast memorize important formulas, such as:

The formula for capacitance (
????
=
????
????
C=
V
Q
​
),
The capacitance of a parallel plate capacitor
????
=
????
????
????
C=ϵ
d
A
​
),
The effects of dielectric materials on capacitance.
These flashcards will help MDCAT students in the concept-building process and also enhance their problem-solving skills for exams.