Hello reader, I welcome you to this article. I am a student of Science and I write articles over different fields of Physics, Chemistry, Biology and etc. Before getting started, I must acknowledge you that the study of Electricity and it’s cause is quite lengthy. For your convenience, I have prepared this article in the simplest manner. So, be patient and read the contents completely. I’m sure it will help you improve your knowledge.
What is electricity? Or, What do we mean by saying Electricity?
For anything to work, energy is needed and energy exists in different forms. Like chemical and mechanical energy, electricity is also a form of energy. From the lightning of a thunderstorm to the bulb glowing in our room, it all happens due to the presence of electricity.
The name ‘electricity’ is derived from the Greek word ‘electron’ meaning amber. But what causes this and how does it work? Whether it is Static electricity or Current electricity, it all arises due to the “state of subatomic particles” and “the amount of charge present on them”. To an electron and a proton, charge is a fundamental property. In the later sections of this article, the significance of the word ‘State’ and ‘Amount’ is discussed clearly. It is more important to focus on the word ‘Charge’ at first! Hence obviously, in order to understand ‘electricity’ a complete understanding of ‘charge’ is needed.
What is charge?
Just like mass and amount of substance, charge is also a fundamental quantity in nature. Consider it as an energy that creates a field around subatomic particles such as electrons and protons. Through this field, these particles interact with each other. An interesting thing to know, is that, the charge of a neutron is neutral or zero!
Classification of charge.
In 1752, the American scientist named Benjamin Franklin conducted his famous kite experiment to show that the lightening in the sky and electric current are the same phenomena. He classified charges into two categories – Positive and Negative. By convention, the charge on a proton is considered positive and the charge on an electron is negative.
Magnitude and behaviour of charge.
The magnitude of charge on an electron is approximately 1.6 × 10^-19 Coulomb or -1 and the magnitude of charge on a proton is also 1.6 × 10^-19 Coulomb or +1. Though the magnitude of charges is equal but they are opposite in nature. Like charges repel each other and unlike charges attract each other. That’s why there is a force of attraction between an electron and a proton.
Charge is conserved and quantized. This means that if Q is the total charge on an object, it can be written as Q=Ne, where N is an integer and e is equal to 1.6×10^-19 Coulomb.
It is well known that negatively charged particles (electrons) reside in outer space while positively charged particles (protons) together with the neutral particles (neutrons) occupy the central space of the atom. Electrons have the ability to move from one atom to another while protons and neutrons stay in their place. This ability of elections is also responsible for the formation of chemical bonds.
To understand Static electricity we move to Electrostatics and to understand Electric current we move to Current-electricity. Electrostatics is the branch of physics that deals with the study of charges at rest while Current-electricity is the branch of physics that deals with the study of charges in motion. Furthermore, to study the properties of AC and DC current along with their sources, the branch of Physics also known as Electromagnetism is considered.
The credit of discovery of the fact that amber rubbed with silk or wool cloth attracts light object goes to Thales from Miletus, Greece, around 600BC.
Take a plastic comb and comb your hair, then suddenly put it near small pieces of paper. You will notice the pieces of paper getting stuck to the comb. This happens due to the attraction between charged particles in the comb and the paper! But how did this happen? While combing the hair, loose electrons from the surface of the hair get transferred to the surface of the comb developing a negative charge on the comb. And when the comb is put near the pieces of paper, the extra electrons put an extra force of attraction on the protons located on the surface of the paper. Thus, attraction happens. Charge can be developed through Induction, Conduction and Friction. Wanna know more about the methods of charging a body? Click at the article below…
As shown in the above diagram, subatomic particles such as electrons and protons with the help of charge in them, develop an electric field around themselves. The field around a proton is directed outwards while the field around an electron is directed inwards. The picture of electric field lines was developed by Faraday. In Electrostatics, the following things are studied –
. The magnitude of an electric field.
. Force due to an electric field (Coulomb’s law).
. Principle of Superposition.
. Dipole moment vector.
. Electric flux (Gaus’s law).
. The potential of an electric field.
. Electrical potential energy.
. van de Graff generator
. The magnitude of an electric field – It is represented by the symbol E and it’s S.I unit is N/C. In free space, the field around a single point charge (at rest) has a magnitude equal to k×q/d^2. Here,
. k = 1/4πε0 = 9×10^9 Newton. Here, ε0 is the permittivity of free space. For vacuum it’s value is 8.854 × 10−12.
. q = Magnitude of charge in Coulomb.
. d = Distance between field and point charge in Meter.
. Force due to an electric field (Coulomb’s law) – It is represented by the symbol F(e) and it’s S.I unit is N.
According to Coulomb’s law, when two point charges q1 and q2 are separated by a distance ‘r’ they put a force on each other. The magnitude of this force can be calculated as – k×q1×q2/r2. Here,
. r is the distance between point charges q1 and q2.
. If the nature of q1 and q2 is the same then the force of repulsion will act.
. If the nature of q1 and q2 are opposite then the force of attraction will act.
. This force is a vector quantity.
. Principle of Superposition –
Suppose if point charges q2, q3, q4 and q5 are collectively putting a force on the point charge q1, then the magnitude of resultant force will be the “vector sum” of of all these individual forces. The magnitude of resultant force can be calculated as – F1 = F21 + F31 + F41 + F51.
. Dipole moment vector – Electric dipole is a combination of two point charges equal and opposite in nature separated by a distance 2a between them. This distance can be a, a/2 or anything else. To find the magnitude of electric field due to this dipole, we need to calculate the dipole moment vector at first! Dipole moment is denoted by P and it can be calculated as P = 2×q×l where, q is the magnitude of one point charge and l is the distance of separation. In this combination, the direction of electric field is from -q to +q. Now, we have two cases,
Case 01 – Magnitude of electric field on the axis of dipole,
At point P on the axis of this dipole, the magnitude of electric field is k×(2P/r^3). The direction of electric field is in the direction of dipole moment.
Case 02 – The magnitude of electric field on the perpendicular bisector of dipole,
At point P on the perpendicular bisector of this dipole, the magnitude of electric field is -k× (P/r^3). The direction of electric field is opposite to the direction of dipole moment.
Now consider if an electric dipole falls inside a uniform electric field. What amount of force will be experienced by the dipole?
The electric field will tend to rotate the dipole on it’s axis such that the direction of dipole moment P is in the direction of electric field E. Thus, the dipole will experience a Torque of the magnitude P × E × Sinθ.
. Electric flux (Gaus’s law)- It is denoted by the symbol φ and it’s S.I unit is Vm. Electric field lines have the ability to pass through any kind of neutral surface. Electric flux is the amount of field lines passing through a surface.
The field lines E make an angle θ with the surface S while passing through it. The combined magnitude of these field lines through the surface is calculated as – φ = E×Area×Cosθ.
Suppose that there is charge ‘q’ inside a closed 3d body. Then according to Gaus’s law, the total electric flux passing through it will be equal to q/ε0. Gaus’s law is helpful in finding the magnitude of electric field due to uniform charge distribution over different surfaces. There is no electric flux passing through a 3d enclosed object until or unless there is an amount of charge inside it.
. The potential of an electric field – It is denoted by the symbol V and it’s S.I unit is J/C. The potential of an electric field can be considered as the strength of the field. For a point charge q it is calculated as – V = k×q/d where,
.q = Magnitude of charge in Coulomb.
. d = Distance between field and point charge in Meter.
. For a positive charge, it’s potential is considered as positive and for a negative charge it’s potential is considered as negative.
. At the axis, the potential of an electric field due to a dipole is + or – k×(P/r^2).
. At the perpendicular bisector, the potential of an electric field due to a dipole is 0.
. For a fixed distance d the potential of an electric field is greater than the magnitude of the field.
The principle of superposition is also applicable for potential due to a system of charges.
. Electrical potential energy – It is denoted by the symbol U and it’s S.I unit is J. It is the energy that is acquired by a point charge when put inside an external electric field. Thus, it’s magnitude can be calculated as – U = k×q×Q/r where,
. r is the distance between point charge q and the external electric field Q.
. If the nature of charge configurations are the same then the potential energy will be positive.
. If the nature of charge configurations are opposite then the potential energy will be negative.
. For a fixed distance r the potential energy of a point charge is greater than the value of electrostatic force experienced by it.
. van de Graff generator – This device was developed by Robert J. Van De Graff. He was an American scientist. The generator is used in building up Static electricity in the form of high voltage.
Charge from the smaller sphere is delivered to the larger sphere through a metal brush. This process is continuously run until the voltage reaches a maximum value of some million units!
. The voltage on the smaller sphere is k×(Q/R + q/r).
. The voltage on the larger sphere is k×(Q/R + q/R).
In 1800 Alessandro Volta invented the battery. His battery was able to generate a tiny amount of electricity through chemical reactions. Later on in 1820, Hans Christian Oersted concluded that electricity and magnetism are interrelated quantities. This was called Electromagnetism and based on these observations, in 1831 Michael Faraday invented the electric motor. Through this motor, he was able to produce electric current through a motion under a magnetic field. Here, the most fundamental question is what is electric current and how does it happen?
Electric current is the flow of charge through a point in a conductor in a certain amount of time. Particles such as electrons are able to move from one atom to another. An amount of charge is associated with each electron and thus, with the flow of electrons, there is a flow of charge.
Current is measured in Ampere, charge is measured in Coulomb and time is measured in Second. Hence, 1Ampere of electric current is the flow of 1Coulomb of charge through a point in 1Second.
Based on the flow of charge, materials can be classified into three categories,
. Conductor – Materials that easily allow the flow of electrons. Examples are : Metals such as Gold, Silver and Copper.
. Semiconductor – Materials that allow only a certain amount of electrons to flow. Examples are : Silicon and Germanium.
. Insulator – Materials that do not allow the flow of electrons. Examples are : Substances such as wood and plastic.
During a thunderstorm, huge amount of free electrons get accumulated at the bottom line of clouds. This leads to a huge amount of potential build-up of around 1 billion volts! Such an amount of energy accumulation is enough to break the barrier of permittivity of air. Thus, air itself becomes the conductor and electrons rapidly move towards the surface of the earth. This phenomenon is visible as lightning bolts across the sky.
While ‘conductivity’ is the allowance of the flow of electrons, ‘resistivity’ is the resistance towards the flow of electrons. Thus, conductors show conductivity but insulators show resistivity.
What is an electrical circuit?
An electrical circuit is a closed loop of conductor consisting of a power source (battery), a resistance and a device that runs on electricity (bulb, fan, motor).
Actually the direction of flow of electrons is from the negative to the positive terminal of the battery but the direction of considered current is from positive to the negative terminal of the battery. The battery has a potential difference and this enables it to push electrons to move in the circuit. Higher the potential, higher is the pushing force. And if the potential difference between two points in a circuit is equal, then there is no charge flowing in it. For an equipment to work, it is necessary that the circuit is closed an there is no short-circuit happening! Grounding is done in order to cope up with excess charge flowing in the circuit.
In current-electricity the following things are studied –
. Ohm’s law
. Combination of resistors.
. Kirchhoff’s law
. Power dissipation in a conductor.
. Capacitor and capacitance.
. Ohm’s law – According to this law, the electric current through a conductor is directly proportional to the potential difference across it. It can be represented as, V = I × R where ‘V’ is the potential difference of the battery, ‘I’ is the current in the circuit and ‘R’ is the resistance in the circuit.
Resistance is represented by the symbol Ω and it’s S.I unit is Ohm. For a material, it’s resistivity can be calculated as, ρ = R×A/L where, ρ is the resistivity, R is the value of resistance offered, A is the area and L is the length. Conductivity is the reciprocal of resistivity and it is calculated as , σ = 1/ρ
Potential difference is represented by V and it’s S.I unit is Volts. It is the difference in amount of electrons across the terminals of the battery. In the negative end there is excess of electrons compared to the positive end of the battery. Electrons tend to move from the zone of excess to the zone of less. Thus, for a battery to power a circuit “difference in potential” is necessary.
. Combination of resistors – Resistors in a circuit can be connected in parallel and series.
In Parallel combination, the potential across each resistor remains the same. The value of final resistance can be calculated as, 1/R = 1/r1 + 1/r2 + 1/r3 + 1/r…
In Series combination, the current across each resistor remains the same. The value of final resistance can be calculated as, R = r1 + r2 + r…
Resistors can be combined in different sets for different purposes. One such combination is ‘Wheatstone bridge’ which is used to find the value of unknown resistance. And similarly, devices such as ‘Meter bridge’ and ‘Potentiometer’ can be operated too.
. Kirchoff’s law – There are two rules, based on which we can analyse any complex electrical circuit. They are as follows,
Junction rule –
It states that the algebraic sum of all currents moving towards a junction (point) in an electrical circuit is equal to the sum of all the currents moving away from the junction. Hence, I1 + I2 = I3 + I4 + I5
Voltage rule –
It states that the algebraic sum of potential difference across all ends in a closed circuit is equal to zero. That is, the sum of potential difference of the battery + resistors + ammeter is equal to zero in both the circuits having current I1 and I2. The direction of current can be considered either clockwise or anti-clockwise.
. Power dissipation in a conductor – It is estimated that around 20% of electrical energy is lost in the form of heat between the power station and our homes. So, whenever there is an amount of current being transferred from one place to another, there is an amount of energy, that is wasted. It is called power loss and it has a relationship with the amount of current and voltage being provided. The relationship is as follows, Pd = P^2 × R/V^2 where –
‘Pd’ is the power loss and ‘P’ is the power generated which is equal to V×I. The S.I unit of power generated is Watt or J/C. So, in order to reduce power loss, high voltage current is supplied. Superconductors are materials that have no electrical resistance and can therefore conduct electricity with no energy loss!
. Ammeter – It is a device which is used to measure the amount of current flowing in a circuit. It measures the amount of current in Amps. The measurement can have errors equivalent to 1% to 2%.
. Voltmeter – It is a device which is used to measure potential difference across the ends of a circuit. The amount of voltage is measured in Volts.
. Potentiometer – It is also a device to measure the value of potential difference at a point in a circuit. It is designed for measuring “unknown voltage” by comparing it with “known voltage”.
. Capacitor and capacitance –
A capacitor is a system of two conductors separated by an insulator. The plates have charges +Q and -Q relatively. They have potentials V1 and V2 respectively. The capacitance C of a capacitor is calculated as, C = Q/V. The value of capacitance of a capacitor depends on the geometry of the conductors also.
In a circuit,
If the individual capacitors are connected in series then the value of total capacitance ‘C’ is calculated as, 1/C = 1/c1 + 1/c2 + 1/c3 + 1/c…
If the individual capacitors are connected in parallel then the value of total capacitance ‘C’ is calculated as, C = c1 + c2 + c3 + c…
The topic of Current electricity can be further elaborated to the types of moving current such as: Alternating current and Direct current and to the sources of ‘electric current’ such as: Conventional generators, Coal powered generators, Wind and Water turbines.
While electricity is an inseparable part of our lives but it should not be underestimated, as it can prove to be fatal if not handled carefully! Thanks…