Electrostatic Potential and Capacitance Physics Class 12 CBSE Notes Study Material Full Chapter 1 Download pdf-ANAND CLASSES
What Is a Capacitor?
A capacitor is a two-terminal electrical device that can store energy in the form of an electric charge. It consists of two electrical conductors that are separated by a distance. The space between the conductors may be filled by vacuum or with an insulating material known as a dielectric. The ability of the capacitor to store charges is known as capacitance.
Capacitors store energy by holding apart pairs of opposite charges. The simplest design for a capacitor is a parallel plate, which consists of two metal plates with a gap between them. But, different types of capacitors are manufactured in many forms, styles, lengths, girths, and materials.
How Does a Capacitor Work?
The most basic structure of a capacitor is the parallel plate capacitor. It consists of two parallel plates separated by a dielectric. When we connect a DC voltage source across the capacitor, one plate is connected to the positive end (plate I) and the other to the negative end (plate II). When the potential of the battery is applied across the capacitor, plate I become positive with respect to plate II. The current tries to flow through the capacitor at the steady-state condition from its positive plate to its negative plate. But it cannot flow due to the separation of the plates with an insulating material.
An electric field appears across the capacitor. The positive plate (plate I) accumulates positive charges from the battery, and the negative plate (plate II) accumulates negative charges from the battery. After a point, the capacitor holds the maximum amount of charge as per its capacitance with respect to this voltage. This time span is called the charging time of the capacitor.
When the battery is removed from the capacitor, the two plates hold a negative and positive charge for a certain time. Thus, the capacitor acts as a source of electrical energy.
The most basic structure of a capacitor is the parallel plate capacitor. It consists of two parallel plates separated by a dielectric. When we connect a DC voltage source across the capacitor, one plate is connected to the positive end (plate I) and the other to the negative end (plate II). When the potential of the battery is applied across the capacitor, plate I become positive with respect to plate II. The current tries to flow through the capacitor at the steady-state condition from its positive plate to its negative plate. But it cannot flow due to the separation of the plates with an insulating material.
An electric field appears across the capacitor. The positive plate (plate I) accumulates positive charges from the battery, and the negative plate (plate II) accumulates negative charges from the battery. After a point, the capacitor holds the maximum amount of charge as per its capacitance with respect to this voltage. This time span is called the charging time of the capacitor.
When the battery is removed from the capacitor, the two plates hold a negative and positive charge for a certain time. Thus, the capacitor acts as a source of electrical energy.
How to Determine the Value of Capacitance?
he conducting plates have some charges Q1 and Q2 (Usually, if one plate has +q, the other has –q charge). The electric field in the region between the plates depends on the charge given to the conducting plates.
We also know that potential difference (V) is directly proportional to the electric field hence we can say,
The amount of electric charge stored in any of the plate of parallel plate capacitor is directly proportional to the potential difference between the two plates of Parallel Plate Capacitor. This relation can be seen as:
Q α V
OR
Q = (constant) V
Where,
C = Capacitance of capacitor
Q = Amount of charge stored in one capacitor
V = Potential difference between the two plates
This constant of proportionality is known as the capacitance of the capacitor.
Capacitance is the ratio of the change in the electric charge of a system to the corresponding change in its electric potential.
The capacitance of any capacitor can be either fixed or variable, depending on its usage. From the equation, it may seem that ‘C’ depends on charge and voltage. Actually, it depends on the shape and size of the capacitor and also on the insulator used between the conducting plates.
he conducting plates have some charges Q1 and Q2 (Usually, if one plate has +q, the other has –q charge). The electric field in the region between the plates depends on the charge given to the conducting plates.
We also know that potential difference (V) is directly proportional to the electric field hence we can say,
The amount of electric charge stored in any of the plate of parallel plate capacitor is directly proportional to the potential difference between the two plates of Parallel Plate Capacitor. This relation can be seen as:
Q α V
OR
Q = (constant) V
Where,
C = Capacitance of capacitor
Q = Amount of charge stored in one capacitor
V = Potential difference between the two plates
This constant of proportionality is known as the capacitance of the capacitor.
Capacitance is the ratio of the change in the electric charge of a system to the corresponding change in its electric potential.
The capacitance of any capacitor can be either fixed or variable, depending on its usage. From the equation, it may seem that ‘C’ depends on charge and voltage. Actually, it depends on the shape and size of the capacitor and also on the insulator used between the conducting plates.
Standard Units of Capacitance
The basic unit of capacitance is Farad. But, Farad is a large unit for practical tasks. Hence, capacitance is usually measured in the sub-units of Farads, such as micro-farads (µF) or pico-farads (pF).
Most of the electrical and electronic applications are covered by the following standard unit (SI) prefixes for easy calculations:
- 1 mF (millifarad) = 10−3 F
- 1 μF (microfarad) =10−6 F
- 1 nF (nanofarad) = 10−9 F
- 1 pF (picofarad) = 10−12 F
The basic unit of capacitance is Farad. But, Farad is a large unit for practical tasks. Hence, capacitance is usually measured in the sub-units of Farads, such as micro-farads (µF) or pico-farads (pF).
Most of the electrical and electronic applications are covered by the following standard unit (SI) prefixes for easy calculations:
- 1 mF (millifarad) = 10−3 F
- 1 μF (microfarad) =10−6 F
- 1 nF (nanofarad) = 10−9 F
- 1 pF (picofarad) = 10−12 F
Parallel Plate Capacitor
Parallel Plate Capacitors are the type of capacitors which are formed by arrangement of electrodes and insulating material (dielectric)
The two conducting plates act as electrodes which are separated by a dielectric between them.
The two plates of parallel plate capacitor are of equal dimensions and is connected to power supply. The plate which is connected to positive terminal of battery acquires positive charge while the plate which is connected to negative terminal of battery acquires negative charge. Due to the attraction charges store between the plates.
Fig.: Parallel Plate Capacitor
Parallel Plate Capacitors are the type of capacitors which are formed by arrangement of electrodes and insulating material (dielectric)
The two conducting plates act as electrodes which are separated by a dielectric between them.
The two plates of parallel plate capacitor are of equal dimensions and is connected to power supply. The plate which is connected to positive terminal of battery acquires positive charge while the plate which is connected to negative terminal of battery acquires negative charge. Due to the attraction charges store between the plates.
Fig.: Parallel Plate Capacitor
Why Parallel Plate Capacitor is used?
Sometimes the electric charge to be stored in a capacitor is of high amount which can’t stored in a single capacitor. So, parallel plate capacitor are used which used two plates as electrodes which help to store more electric charge.
Principle of Parallel Plate Capacitor
As we know that certain amount of charge can be given to a plate as if more charge is applied its potential will increase and charge might leak.
If we get another plate and place it next to this positively charged plate then negative charge will be pulled towards the side of this plate which is closer to the positively charged plate and positive charge on the further side.
Fig.: Two plates of parallel plate capacitor
As both the plates have charges the negative charge on plate 2 will reduce the potential difference on plate 1 while the positive charge on plate 2 will increase the potential difference on plate 1. But the negative charge on plate 2 will have more impact.so more charge can be given on plate 1 because of negative charges on plate 2 the potential difference will be less.
Fig.: Plates of parallel plate capacitorThis is the principle of parallel plate capacitor.
Charging of Parallel Plate Capacitor
Fig.: Circuit for charging capacitor
Let C be the two plates of capacitor, V be the potential difference and k be the switch in figure 4.
Now when the key is closed then the electrons from the first plate start moving towards the positive end of the battery that is, there is flow of electrons from negative end to positive end of the battery
The electrons which moved towards to the positive end of battery from there they will start moving towards to the second plate. In this way both the plates will acquire charges, one will acquire positive charge while other will acquire negative charge.
This process will continue until the capacitor acquires potential difference V in the exact same amount that of the battery. Now the process will stop. At this time when the process has been stopped the capacitor has stored electric charge on it with the potential difference which is same as battery.
So now the charge can be written as:
Q = CV
Sometimes the electric charge to be stored in a capacitor is of high amount which can’t stored in a single capacitor. So, parallel plate capacitor are used which used two plates as electrodes which help to store more electric charge.
Principle of Parallel Plate Capacitor
As we know that certain amount of charge can be given to a plate as if more charge is applied its potential will increase and charge might leak.
If we get another plate and place it next to this positively charged plate then negative charge will be pulled towards the side of this plate which is closer to the positively charged plate and positive charge on the further side.
Fig.: Two plates of parallel plate capacitor
As both the plates have charges the negative charge on plate 2 will reduce the potential difference on plate 1 while the positive charge on plate 2 will increase the potential difference on plate 1. But the negative charge on plate 2 will have more impact.so more charge can be given on plate 1 because of negative charges on plate 2 the potential difference will be less.
Fig.: Plates of parallel plate capacitor
This is the principle of parallel plate capacitor.
Charging of Parallel Plate Capacitor
Fig.: Circuit for charging capacitor
Let C be the two plates of capacitor, V be the potential difference and k be the switch in figure 4.
Now when the key is closed then the electrons from the first plate start moving towards the positive end of the battery that is, there is flow of electrons from negative end to positive end of the battery
The electrons which moved towards to the positive end of battery from there they will start moving towards to the second plate. In this way both the plates will acquire charges, one will acquire positive charge while other will acquire negative charge.
This process will continue until the capacitor acquires potential difference V in the exact same amount that of the battery. Now the process will stop. At this time when the process has been stopped the capacitor has stored electric charge on it with the potential difference which is same as battery.
So now the charge can be written as:
Q = CV
What Are the Applications of Capacitors?
Capacitors for Energy Storage
Since the late 18th century, capacitors have been used to store electrical energy. Individual capacitors do not hold much energy, providing only enough power for electronic devices during temporary power outages or when they need additional power. Many applications use capacitors as energy sources, and a few of them are as follows:
- Audio equipment
- Camera Flashes
- Power supplies
- Magnetic coils
- Lasers
Supercapacitors are capacitors that have high capacitances up to 2 kF. These capacitors store large amounts of energy and offer new technological possibilities in areas such as electric cars, regenerative braking in the automotive industry and industrial electrical motors, computer memory backup during power loss, and many others.
Since the late 18th century, capacitors have been used to store electrical energy. Individual capacitors do not hold much energy, providing only enough power for electronic devices during temporary power outages or when they need additional power. Many applications use capacitors as energy sources, and a few of them are as follows:
- Audio equipment
- Camera Flashes
- Power supplies
- Magnetic coils
- Lasers
Supercapacitors are capacitors that have high capacitances up to 2 kF. These capacitors store large amounts of energy and offer new technological possibilities in areas such as electric cars, regenerative braking in the automotive industry and industrial electrical motors, computer memory backup during power loss, and many others.
Capacitors for Power Conditioning
One of the important applications of capacitors is the conditioning of power supplies. Capacitors allow only AC signals to pass when they are charged, blocking DC signals. This capacitor effect is used in separating or decoupling different parts of electrical circuits to reduce noise as a result of improving efficiency. Capacitors are also used in utility substations to counteract inductive loading introduced by transmission lines.
One of the important applications of capacitors is the conditioning of power supplies. Capacitors allow only AC signals to pass when they are charged, blocking DC signals. This capacitor effect is used in separating or decoupling different parts of electrical circuits to reduce noise as a result of improving efficiency. Capacitors are also used in utility substations to counteract inductive loading introduced by transmission lines.
Capacitors as Sensors
Capacitors are used as sensors to measure a variety of things including humidity, mechanical strain, and fuel levels. Two aspects of capacitor construction are used in the sensing application – the distance between the parallel plates and the material between them. The former detects mechanical changes such as acceleration and pressure, and the latter is used in sensing air humidity.
Capacitors are used as sensors to measure a variety of things including humidity, mechanical strain, and fuel levels. Two aspects of capacitor construction are used in the sensing application – the distance between the parallel plates and the material between them. The former detects mechanical changes such as acceleration and pressure, and the latter is used in sensing air humidity.
Capacitors for Signal Processing
There are advanced applications of capacitors in information technology. Capacitors are used by Dynamic Random Access Memory (DRAM) devices to represent binary information as bits. Capacitors are also used in conjunction with inductors to tune circuits to particular frequencies, an effect exploited by radio receivers, speakers, and analog equalizers.
There are advanced applications of capacitors in information technology. Capacitors are used by Dynamic Random Access Memory (DRAM) devices to represent binary information as bits. Capacitors are also used in conjunction with inductors to tune circuits to particular frequencies, an effect exploited by radio receivers, speakers, and analog equalizers.
Frequently Asked Questions on Capacitors and Capacitance
Q1
What is a variable capacitor?
A variable capacitor is a capacitor whose capacitance can be varied to a certain range of values based on necessity. The two plates of the variable capacitor are made of metals where one of the plates is fixed, and the other is movable. Their main function is to fix the resonant frequency in the LC circuit. There are two types of variable frequency and they are, tunning capacitors and trimming capacitors. Q2
How does the shape of the capacitor affect its capacitance?
- The distance between the plates
The more distant the plates are, the less the free electrons on the far plate feel the push of the electrons that are being added to the negative plate. This makes it harder to add more negative charges to the negative plate. The current will flow through a short circuit if the plates are closer. This implies that the capacitance of a parallel plate is inversely related to the plate separation.
- Area of the plates
It’s easier to add charges to a capacitor if the parallel plates have a huge area. Two wide metal plates would give two repelling-like charges a greater range to spread out across the plate, making it easier to add a lot more negative charges to one plate. Likewise, a very small plate area would cause the electrons to get cramped together earlier, making it harder to get a large difference in charge for a given voltage.
Q3
- The distance between the plates
The more distant the plates are, the less the free electrons on the far plate feel the push of the electrons that are being added to the negative plate. This makes it harder to add more negative charges to the negative plate. The current will flow through a short circuit if the plates are closer. This implies that the capacitance of a parallel plate is inversely related to the plate separation.
- Area of the plates
It’s easier to add charges to a capacitor if the parallel plates have a huge area. Two wide metal plates would give two repelling-like charges a greater range to spread out across the plate, making it easier to add a lot more negative charges to one plate. Likewise, a very small plate area would cause the electrons to get cramped together earlier, making it harder to get a large difference in charge for a given voltage.
What are Ultracapacitors?
An ultracapacitor, also known as the supercapacitor, is a high-capacity capacitor with a capacitance value much higher than other capacitors but with lower voltage limits. Q4
How long does a capacitor last?
Capacitors have a limited life span. Most capacitors are designed to last approximately 20 years. Q5
What kind of energy is stored in a capacitor?
Energy stored in a capacitor is electrical potential energy, thus related to the charge Q and voltage V on the capacitor. Q6
Why isn’t water used as a dielectric in a capacitor?
Water has a high dielectric constant but a very low dielectric strength, hence it would act as a conductor and leak charges through it.
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