Electric charge is a core quality of matter that plays a role in producing electric effects and interactions. It has the same properties as mass and time and is a foundation for functioning electric fields, currents, and electromagnetic forces.
Charges are found in two forms: Both kinds of charge and the way they interact lead to many of the phenomena observed in physics involving electricity and magnetism.
In nature, the amount of charge cannot change, but it can be transferred from one body to another. Electric charge is essential in exploring electromagnetism because it plays a significant role in this phenomenon, which is also known as one of the major forces in the universe.
What is Electric Charge
Any object in nature is neutral. If someone walks on a carpet in an area with low humidity, then there is a slight charge imbalance in that person’s body.
and the feeling of this charge is not known until it comes in contact with another person or the earth. When that person comes in contact with someone, it generates a slight shock and spark.
Static electricity deals with phenomena of attractions or repulsions of electric charges.
Discovery and historical background of electric charge
The idea of charge dates back a long way. It is said that around 600 BCE, Thales of Miletus, a Greek philosopher, realized that rubbing amber and fur mixed could attract small objects.
It was one of the first times that anyone noted the effects of static electricity. Electricity came from the Greek word “Elektron,” meaning amber.
In 1600, William Gilbert, an English scientist, named electricity and made it clear that it was distinct from magnetism. Eventually, in 1733, Charles du Fay discovered that there are two kinds of charge: positive and negative.
Benjamin Franklin proposed around the mid-1700s that all electricity consists of one fluid and introduced the names positive and negative for the charges. His kite experiment, which showed that lightning is electricity, made his work famous.
The 19th century saw significant advancements. Because of Alessandro Volta’s invention, the first battery had a continuous electric current. Michael Faraday explained what is known as the electric field and electromagnetic induction.
In 1897, J.J. Thomson was the first to discover the electron, a negatively charged particle. This discovery contributed to our understanding of charge and proved that electric charge is an important feature of matter itself.
Types of Electric Charge
There are two types of charge:
- Positive Charge
- Negative Charge
Positive Charge
One of the main types of charge is a positive charge, with the negative charge being the other. Protons are located in an atom’s nucleus and help give it its positive ion.
When an object loses electrons and has fewer of them than the number of protons it contains, it gets a positive ion.
For example, rubbing a glass rod with silk will cause some of the glass’s electrons to move to the silk. After giving up its negatively charged electrons, the glass rod takes on an electropositive charge.
Characteristics of positive charge
- A positively charged object will draw negatively charged objects to itself while driving positively charged objects apart. The basic idea of charges is that opposite charges attract each other and like charges repel.
- We measure positive proton using a coulomb (C), and the amount of charge on a proton is about +1.6 × 10⁻¹⁹ C.
- While electrons can move freely in most materials, cation cannot. Yet, when materials are ionized or in electrolytes, positive ions can carry an electric current.
Negative Charge
Negative ion is one of the main types of electric charge, with the other being positive ion. Subatomic particles called electrons carry the negative ion in an atom as they orbit the nucleus.
If a thing gains extra electrons, it will have more electrons than protons and become negatively charged.
For example, when a plastic rod comes into contact with wool, electrical charges from the wool are transferred to the rod.
For this reason, the rod is negatively charged because it has more electrons than before.
Characteristics of negative charge
- Like charges repel, and unlike charges attract. This interaction produces things like static electricity and electric current.
- Electrons are the smallest charge particles, and each one has a negative charge of −1.6 × 10⁻¹⁹ C.
- Negative electrons can move in conductors and have important functions in electricity, electronics, and electromagnetic theory.
Value of Electric Charge
Negative electrons and mesotrons make the smallest type of negative charge. its value is -1\cdot 60\times 10^{-19} coulomb.
The smallest type of positive cation is made by positron and its value is +1\cdot 60\times 10^{-19} coulomb.
In any current-flowing conductor, a positive ion appears when there is a dearth of electrons. The transfer of charge, positive and negative, both types of charge take part in conduction.
A point charge is an electric charge that is spread or distributed along a line, on a surface, or in a volume. Therefore, there are four types of charge.
1. Point Charge
When the dimensions of a surface carrying charge are very, very small compared to the region surrounding it, then the surface can act as a point. Therefore, this charge is called a point charge. The point charge is a point, but it does not have the dimensions—point charges like positive or negative.
2. Line Charge
When the static charge may be spread all along a line, it is called a line charge. It may be finite or infinite.
3. Surface Charge
When the static charge is distributed uniformly over a dimensional surface, it is called surface charge in the figure shown surface charge.
4. Volume Charge
When a charge is distributed uniformly in a volume, then this charge is called a volume charge. The figure shows the volume charge.
Electrostatic
Electrostatics involves the study of how electric charges behave when left alone. It examines the interaction of stationary charges with each other and the types of forces they exert.
Rubbing two objects against each other causes the electrons in them to move toward each other, resulting in electrostatic charges. This leaves one object with an extra electron and the other with one less electron.
Coulomb’s Law implies that opposing charges are attracted and identical charges are repelled by each other. How powerful the force is depends on how much charge there is and the space between the two objects.
Another concept in electrostatics is the electric field, which is where other charges can notice a charged object’s effect.
Examples of electrostatics being used include photocopy machines, air purifiers, and painting using electricity. It also helps explain how lightning and static electricity occur.
Application of Electrostatic
Power plant: These devices, which are found in power plants and factories, use static electricity to get rid of dust and smoke from exhaust gases, thus keeping the air clean and cutting down on pollution.
Much like that, air purifiers depend on electrostatic filters to take out dust, pollen, and other particles from the air, ensuring that the air inside the building is healthier to breathe.
Spray painting: This method is often used for electrostatic spray painting as well. In this case, paint droplets pick up an electrical charge and are shot onto a metal surface that is connected to an electrical ground.
Using the charged paint ensures that the paint goes onto the surface smoothly and cuts down on wastage. Electrostatic sprayers in agriculture help pesticides and fertilizers coat the crop more evenly. Electrostatics is used in inkjet printers to regulate how much ink comes out and create fine images.
Touchscreen technology: Touchscreen technology works thanks to changes in the electrostatic field caused by the user touching the screen. In nature, the occurrence of lightning can be explained by electrostatics, as it happens when charge builds inside clouds.
Coulomb's Law or Electric Charge Law
In the 18th century, French Scientist Charles A. Coulomb studied charge and discovered two rules of electric charge. This law is also called electrostatics, Coulomb’s law, or charge law.
In electrostatics, Coulomb’s Law explains how two stationary charges relate to each other through force. It was created by French physicist Charles-Augustin de Coulomb in 1785. The law states that:
- Like charges repel each other and unlike charges attract each other
We can understand the rule with simple examples.the ebonite rod becomes negatively charged when rubbed against fur cloth.
Again, if glass rod is rubbed againsts fur cloth, it gets positively charged. if they are brought near each other,they try to attract each other.
When two ebonite rods after rubbing against fur cloth, brought nearby, try to repel each other.
An electrostatic unit of charge is that charge which, when placed one centimeter away from a like charge in a vaccum,repels it with a force is called one dyne.
- Coulomb's Inverse Square law.
According to this rule, the mechanical force between two small charge bodies, whether it is attraction or repulsion.
- Directly Proportional to the Product of the Charged between the two bodies
- Inversely Proportional to the Square of the distance between the bodies.
- Depends upon the nature of the medium surrounding the bodies.
In figure two point charges, separated by distance d meter.the charges are Q_{1} and Q_{2} coulombs and K is the content of proportionality.according to coulomb’s law, force between the charges can be expressed as
F\propto \dfrac{Q_{1}Q_{2}}{d^{2}}
F=\dfrac{KQ_{1}Q_{2}}{d^{2}}
The constant of proportionally,K depends on the surrounding medium and is given by
k=\dfrac{1}{4\pi \varepsilon }=\dfrac{1}{4\pi \varepsilon _{r}\varepsilon _{0}}
where \varepsilon = absolute permittivity of medium = \varepsilon _{0}\varepsilon _{r}
\varepsilon _{0} =permittivity of free space
and \varepsilon _{r} =Relative Permittivity of the medium
\varepsilon _{0} =\dfrac{1}{36\pi \times 10^{9}}
8.854\times 10^{-12} farad per meter.for air \varepsilon _{r} = 1
the concept of permittivity is discussed later in the chapter.if Q_{1}=Q_{2}=1c and d=1m.
then F=\dfrac{1}{4\pi \times 8\cdot 854\times 10^{-12}}=9\times 9^{9}N.
Properties of Electric Charge
Charge is a characteristic of matter that accounts for the presence of electric forces and fields. It exists in two types: positive and negative. Essential attributes of charge include the following:
- Quantization of Charge: Charges only come in whole units or multiples. An elementary charge is either the charge possessed by an electron or that of a proton. The charge on anybody can be represented as a whole number times the elementary charge. Q=n⋅eQ ( n is an integer)
- Conservation of Charge: Isolated systems maintain the same amount of electric charge. Charge can neither be created nor destroyed. However, it can only be redistributed between objects. The total charge remains the same in an isolated system before and after interactions.
- Additivity of Charge: Charges are added mathematically by summing the values. A system’s net charge is obtained by adding together the charges of all the individual point charges in the system.
- Attraction and Repulsion: Charges with the same sign will push away from each other, while those with different signs will pull each other. According to Coulomb’s Law, the force pulls or pushes the two charges toward each other or apart.
- Invariance of Charge: The value of charge does not change regardless of the observer’s frame of reference. Therefore, the charge does not change depending on whether the body is stationary or moving.
SI Unit of Electric Charge
The SI unit of electric charge is the coulomb. A coulomb equals the quantity of charge passed by a current of one ampere in one second.
1 C=1 A×1 s
Electric Charge Formula
The fundamental formula for charge is the following:
Q = I × t
Where:
- Q is the charge expressed in coulombs.
- The current is given in amperes or A.
- t represents time in seconds.
Electric charge is the product of current time. Because of continuous current flow, it is crucial to know how charge changes in circuits.
Charge quantization is expressed as follows:
Q = n × e
Where:
n represents the number of electrons or protons in a given instance. (1 elementary charge is equal to 1.6×10^-19 C.)
Dimensional Formula of Electric Charge
The dimensional formula of electric charge can be obtained by following this equation.
Fundamental formula:
Q = I.t
The dimention of electric charge is :
[A].[T] = [A.T]
Where :
[A] is the dimension of electric current.
[T] is the dimension of time.
then dimensional formula of charge is [AT]
Electric Charge and Field
The Electric Field is where the force on other charges appears because of a charged object. It is shown as a vector quantity E. For a point charge Q, the electric field at a distance r is given using the expression:
E=\dfrac{1}{4\pi \varepsilon _{0}}
Where \varepsilon _{0} is the permitivity of free space ( 8.854\times 10^{-12} C^{2}/N-m^{2})
Electric field lines run away from a positive ion and toward a negative ion. Electric field lines draw the field and make it understandable. They travel straight, and their number shows the field’s strength.
Many applications such as capacitors, electric circuits and electrostatics, depend greatly on electric fields, forming the base of electromagnetic theory.
What is Electric Lines of Force
An electric field is generated around any charge, and we display it by imaging, and it is called the lines of force. The lines of force of positive ion and negative ion are shown in the figure.
Such lines of force originate from the electropositive charge and terminate on the electronegative charge. When these two types of charges are brought together, they exert the force of attraction on each other.
Some Important Properties of lines of force.
- the lines of force alaways originate from a + ve charge and terminate at - ve charge.
- lines originate or terminate from a charged particle never cross each other
- the lines traveling in the same direction repel each other,while traveling in the opposite directions attract one another.
- it alaways behave like stratched band
- they are alaways parallel.
- they alaways pass in insulating medium.
Electric Field
If another charge is established inside the field of any charge, then there is a stress and a force between them, whether both charges are of an equal or unequal nature.
The area around which force or stress is applied in charge body is called electric field. such electric field produced due to stationary electric charge it does not very with time. it is time invariant and also called static electric field.
Electric flux represented by \psi. the unit of electric flux is also coulomb C
Superposition Principle
According to Coulomb’s law, the force between two charges is either attraction or repulsion. But if many charges are present simultaneously, then in this situation, the superposition principle is used to find the force on the particular charge.
When multiple charges are present, the total force on the given charge is equal to the vector, the sum of forces, due to other charges remaining on a given charge.
The use of Superposition Principle to find
- net electric force due to a number of charges
- net electric flux due to a number of charges
- net electric field due to a number of charges
- net electric potential due to a number of charges
- net electric potential energy due to a number of charges
Electric Field Due to a Point Charge
An electric field describes the area in which a charged object pulls or pushes on nearby charges. The electric field for a point charge is found by seeing how much a tiny positive test charge is affected near the main charge and sharing the results by the test charge’s mass.
Mathematically, E = (k\times |q|)/r^{2}
Where:
- Eis the electric field
- q is the point charge
- r is the dimension from the charge
- k is coulomb’s constant
Electric Field Due to Line Charge
Commonly, a line charge represents an infinite thin wire that spreads charge along a line. The linear charge density (labeled as λ ) refers to how much charge is held in a certain length, and its measurement is given in coulombs per meter (C/m).
Formula:
The electric field at a plane perpendicular to the wire and a distance r from a straight infinitely long charged wire equation is:
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Electric Potential due to a Point Charge
Electric potential tells us how much work (per unit positive test charge) it would take to move something from infinity to that point without causing any acceleration in an electric field. Its unit is called volts (V), and it is scalable.
Formula:
When a point charge QQ is surrounded by vacuum, the electric potential VV at a distance or from the charge is given by:
V = \dfrac{1}{4\pi \varepsilon _{0}}.\dfrac{Q}{r}
Where:
- V = electric potential in volts,
- Q = Source charge in cloumb’s,
- r = distance from charge in meters,
- \varepsilon _{0} = permitivity of free space ( 8.854\times 10^{-12} C^{2}/N-m^{2})
Important Role of Electrostatics Principle
- these principle used in cathode ray tube for focusing and deflecting a beam.
- these principle used in computer peripheral devices like keyboards,touch pads and liquid crystal displays etc.
- these principle used in X-ray machine and medical instruments used for electrocardiograms,scanning etc.
- these principle used in spray painting,electrodeposition etc.
- these principle used in the agricultural activities like sorting seeds,spraying to plants etc.
- these principle used in resistors,capacitors and transistor functioning.
Important Points:
- Positively charged particles experience a positive electric potential, whereas negatively charged particles experience a negative electric potential.
- It drops as the distance rr increases. The farther away the objects are, the less potential they have.
- At infinity, the probability of the event is seen as zero.
Nature of Electric Potential:
Unlike the electric field, an electric potential is a scalar so that we can add potentials from several charges simply by addition.
Equipotential Surfaces:
The term equipotential surfaces refers to areas where the electric potential does not change. Points on concentric spheres centred at the charge represent a point charge. Moving a charge along an equipotential surface does not take any effort.
Conclusion
Charge plays a key role in physics and is closely involved in the processes of electric and magnetic activities. Coulomb’s Law is just one example of the laws that control the positive or negative types of this force. The field of electrostatics, which explores electric charges and what they do, can explain matters ranging from subatomic behavior to how electronic devices operate.
A good understanding of charge ele,ctric field, and potential is crucial for moving forward in electromagnetism, electrical engineering and modern physics.
FAQ :-
1. Who Discovered Electric Charge
The credit for discovering the electric charge is given to Benjamin Franklin. You simplified the concept of electric charge and introduced terms like positive and negative charge.
2. What is Static Electricity
Static electricity is generated when there is an imbalance between positive and negative charges in substances. This imbalance is usually caused by friction, where electrons are transferred from one object to another. For example, when we rub a balloon on our hair, the static electricity causes the balloon to attract small pieces of paper.
3. What is the cgs Unit of Electric Charge
The CGS unit of electric charge is the statcoulomb. The statcoulomb is defined based on the electrostatic force between charges. This means two charges of 1 statC each, placed 1 cm apart in a vacuum, exert a force of 1 dyne on each other.
4. Why is electric charge a scalar quantity?
Electric charge is a scalar quantity because it has only magnitude and no direction. Because vector quantities (e.g., force or velocity) require both magnitude and direction.
5. Is electric charge conserved?
Yes, electric charge is conserved. The principle of conservation of charge is a fundamental law of physics. This principle states that charge can neither be created nor destroyed; it can only be transferred from one object to another.
6.What is the electric charge of the clouds?
Cloud charge varies depending on the weather conditions, particularly during thunderstorms.
- In a thunderstorm cloud, The upper part of the cloud tends to accumulate a positive charge, while the lower part of the cloud builds up a negative charge.
- The negative charge in the lower part of the cloud induces a positive charge on the Earth’s surface below it, creating the conditions for lightning.
I am an engineer in a government department and also a blogger. I write posts on topics related to electrical and electronics engineering.