Electric Charges and its Basic Properties: Definition, Conservation, and Quantization

Electric Charges and its Properties: Electricity is a basic requirement for all of us. Our devices, machines, and networks are all powered by it. Electricity is nothing but the flow of electric charges. Rubbing two surfaces across each other can produce electric charges due to friction; these can be induced on a neutral surface when a charged body is brought close to it, or these can be transferred from one conducting surface to another. The presence of electric charges can be experienced in our day-to-day lives.

Lightning strikes that light up the sky involve the discharge of electric charges on the order of several million volts! You have probably even experienced an electric shock when you touch a doorknob or woollen clothes. Without electricity, civilization as we know it would collapse. There would be no Youtube, Instagram, transportation, connectivity that civilization has come to rely on and take for granted. Although several scientists independently discovered electricity, Benjamin Franklin is often credited with its discovery. In \(1752,\) he conducted a test on a rainy day, in which he flew a kite with a key at the other end, which he held. He experienced an electric shock, which was nothing but the flow of electric charge.

Contrary to popular belief, the kite was not struck by lightning. That would have been disastrous; the lightning would have electrocuted him. The kite actually picked up ambient atmospheric charge, which was mild in comparison to a lightning strike. Let us learn in detail about electric charges and their properties.

Electric Charges

Electric charge is the basic physical property of all matter due to which it experiences a force when it is placed in an electromagnetic field. Electric charges can also be understood as the amount of energy or electrons that transfer from one system to another. This transfer of electrons can occur through different processes like conduction, induction, or certain specific methods. Electric charges on a surface can be of two types: \((+)\) positive charge and \((-)\) negative charge.

Charges are considered to be ubiquitous, i.e., present almost everywhere. A surface without any charge either has absolutely no charge present on it, or it may be neutral, i.e., it contains an equal number of negative and positive charges. The basic subatomic particles present almost on all surfaces are electrons (which possess the negative charge), protons (which possess the positive charge), and neutrons (which possess a neutral charge).  We use the letter \(‘q’\) or \(‘Q’\) to represent charges. 

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The total amount of charge present on a surface equals the product of the number of charges and the charge on each electron. Mathematically, it can be given as:

\(Q=n×e\)

Here,

\(Q:\) Total charge

\(n:\) Number of charges

\(e:\) charge on each electron.

Charge on each electron \(1e = 1.6 \times {10^{ – 19}}{\rm{C}}\)

The SI unit of electric charge is the coulomb \(({\rm{C}}).\) The charge on a system is one coulomb when a current of one ampere flows through the system in one second. One coulomb is a huge amount of charge. It is equal to the charge on \(6 \times {10^{18}}\) electrons. In general, we use the following units:

Milli-coulomb: \(1\,{\rm{mC}} = {10^{ – 3}}\,{\rm{C}}\)

Micro-coulomb: \(1\,\mu{\rm{ C}} = {10^{ – 6}}\,{\rm{C}}\)

Properties of Electric Charges

Electric charges resemble magnetic poles in their two main basic properties, and these are:

Like charges repel each other.

Unlike charges attract each other.

Consider the following example: Two protons kept in close contact repel each other, and two electrons kept in close space repel each other. But when a proton is kept near an electron, the two charges will attract each other.

Characteristics of Electric Charges

Since the charges of subatomic particles like electrons, protons, and neutrons are infinitely small compared to the size of bodies we deal with, the electric charges can be considered to be point-sized. The electric charges can flow from one point to another, and this flow is responsible for electricity. The general properties of electric charges are:

1. Electric charge is a scalar: Electric charge is a scalar quantity even though it has both magnitude and direction. This is because a quantity is a vector if it follows the laws of vector addition like triangle law and parallelogram law. Electric current does not follow the laws of vector addition. When two currents meet at a junction, the net current at that point is the algebraic sum of the currents and not the vector sum. Since the current is the flow rate of electric charges per unit time, electric current and hence charge is a scalar.

2. Electric charge is transferrable: Electric charge can be transferred from an uncharged body to a charged body. It is usually electrons that are responsible for the flow of charge as they aren’t as tightly bound as protons in an atomic nucleus. An uncharged body that loses electrons becomes positively charged, while an uncharged body that gains electrons becomes negatively charged.

3. There is mass associated with electric charge: Electric charge cannot exist without mass, but there exists mass without charge. When electric charges are transferred from one body to another, there is a change in the body’s mass, although the change in mass is extremely small compared to the body’s mass.

4. Electric charge is invariant: The charge on a body is independent of the frame of reference, i.e., the charge on a body does not vary with speed. 

5. Accelerated charges radiate energy: An accelerated charge in motion generates both electric and magnetic fields, radiating energy in the form of electromagnetic waves.

Additive Nature of the Charge

Electric charges are additive in nature, and the addition of electric charges depends upon the charges’ nature. Additive property is scalar in nature, and it is possible to add the electric charges directly. To understand this, consider a system containing two electric charges \({Q_1}\) and \({Q_2}\).

According to this property, 

The total charge on the system will be equal to the algebraic sum of individual charges of the system. Thus, mathematically,

The total charge of the system, \({Q_{{\rm{total }}}} = {Q_1} + {Q_2}\)

When the system consists of multiple charges, the same law holds true. Thus, for a system consisting of charges \({Q_1},{Q_2},{Q_3} \ldots {Q_n}.\) Thus, mathematically,

The total charges of the system, \(Q = {Q_1} + {Q_2} + {Q_3} \ldots {Q_n}\)

Conservation of Charge

The electric charge on a system is conservative in nature. In other words, total charge can neither be created nor destroyed. The electric charges can only be transferred from one system to another or from one body to another by the methods of conduction, induction or friction. For example, rubbing involves the transfer of charges from one surface to another, and as a result, one body becomes negatively charged while the other becomes equally positively charged. But the total charge on the system of two bodies remains conserved. This law is similar to the conservation of mass or the first law of thermodynamics, also known as the law of conservation of energy.

Consider the following example:

A system contains a total charge of \(5\,{\rm{C}}.\) This charge can be redistributed as \(1\,{\rm{C}}\) and \(4\,{\rm{C}}\) or in several other combinations based on the law of conservation. The transfer of electrons will occur between the bodies so that the total charge on the system remains the same. The same scenario is seen in the case of neutrino decay. 

During a neutrino decay, a neutron loses an electron and proton each. The total charge on the system will be equal to the sum of charges on both the electron and the proton; since the charges on both are equal and opposite, the total charge on the system will be zero.

Quantization of Charge

The total charge on any given surface is quantized, i.e., the net charge on a surface can be expressed as an integral multiple of the charge on an electron, i.e., \(1.6 \times {10^{ – 19}}\,{\rm{C}}.\) If the total charge on a system is \(Q,\) then this can be given as:

\(Q = n \times e\)

Here, \(n\) is an integer

\(e\) is the charge on an electron

English scientist Faraday first proposed the quantization of electric charge based on his experimental laws of electrolysis. In \(1909,\) this principle was demonstrated and proved by Millikan. We extensively use the quantization concept to calculate the total amount of electric charge on a system. 

Consider a surface containing \({N_1}\) protons and \({N_2}\) electrons. Using the quantization law, 

The net amount of charge, \({Q_{net}} = {N_1}( + e) + {N_2}( – e)\)

Thus, \({Q_{net}} = \left( {{N_1} – {N_2}} \right)e\)

Solved Examples on Electric Charges and Their Properties

Q.1. A body consists of \(5\) subatomic particles, \(3\) positively charged and \(2\) negatively charged. The charge present on these six particles are \(+4\,{\rm{C}},+10\,{\rm{C}},+6\,{\rm{C}},- 4\,{\rm{C}}\) and \(-2\,{\rm{C}}.\) What is the net charge on the body?
Ans: Using the additive property of electric charge, the net charge of a system is the algebraic sum of charges on the individual subatomic particles.
Thus, Total charge of the system, \({Q_{{\rm{total }}}} = + 4\,{\rm{C}} + 10\,{\rm{C}} + 6\,{\rm{C}} + ( – 4\,{\rm{C}}) + ( – 2\,{\rm{C}})\)
\({Q_{{\rm{total }}}} = 14\,{\rm{C}}\)

Q.2. Two particles \(A\) and \(B\), having charges \(10\,{\rm{C}}\) and \(4\,{\rm{C}}\) are rubbed against each other. If during the rubbing, five coulombs of charge from body \(A\) are transferred to body \(B.\) Calculate the final charges on the two bodies.
Ans: Using the principle of conservation of electric charges, the net charge on the system of the two bodies will remain conserved. Thus, the charge lost by \(A\) will be gained by \(B.\)
Thus, the final charge on body \(A,10\,{\rm{C}} – 5\,{\rm{C}} = 5\,{\rm{C}}\)
Final charge on body \(B,\,4\,{\rm{C}} + 5\,{\rm{C}} = 9\,{\rm{C}}\)

Summary

Electric charge is the basic physical property of all matter due to which it experiences a force when it is placed in an electromagnetic field. Electric charges on a surface can be of two types: \((+)\) positive charge and \((-)\) negative charge. The total amount of charge present on a surface equals the product of the number of charges and the charge on each electron. Mathematically, it can be given as \(Q=n×e\)

Electric charges are additive, and the addition of electric charges depends upon their charges’ nature. According to this property, the total charges on the system will be equal to the algebraic sum of individual charges of the system.

The electric charge on a system is conservative. In other words, a charge can neither be created nor destroyed. The electric charges can only be transferred from one part of a system to another or from one body to another by conduction, induction, or friction.The total charge on any given surface is quantized, i.e., the net charge on a surface can be expressed as an integral multiple of the charge on an electron, i.e., \(1.6 \times {10^{ – 19}}\,{\rm{C}}.\)

Frequently Asked Questions (FAQs) on Electric Charges and its Basic Properties

Q.1. Write the three basic properties of electric charge.
Ans: The properties are:
1. Electric charges are additive.
2. Electric charges are always conserved.
3. Electric charges are quantized.

Q.2. Is the electric current a scalar or vector?
Ans: Electric current is a scalar quantity.

Q.3. Explain quantization of charge.
Ans: According to the principle of quantization of charge, the total charge on a surface is an integral multiple of the charge on an electron.

Q.4. What is the S.I. unit of electric charge?
Ans: The S.I unit of charge is coulomb \(({\rm{C}}).\)

Q.5. What do you mean by conservation of charge?
Ans: Charge conservation means that the charge can neither be created nor destroyed, i.e. it can only be transferred from one body to another.

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