Electricity is a very important form of energy which can be easily converted into other forms of energy. Electricity can be produced at one place and can be transmitted to long distances. Electricity is a branch of Physics which deals with charges, stationary and moving. For convenience, electricity is divided into two types: static electricity and current electricity. The pioneers of this branch Physics are Gilbert, Thale, Faraday, Benjamin Franklin, Ampere, Volta, Coulomb, Thevenin, and Maxwell.

Structure of Atom:

An atom consists of positively charged protons, negatively charged electrons, and neutral neutrons. The total number of protons in an atom is equal to the total number of electrons. Thus net positive charge balances the net negative charge. Hence atom is electrically neutral.

Protons and neutrons are present in central core called nucleus. Hence nucleus carries a positive charge. The negatively charged electrons revolve around the positively charged nucleus in circular orbits. There is force attraction between the negatively charged electrons and the positively charged nucleus which provides the necessary centripetal force for the circular motion of electrons around the nucleus.

The attractive force between the electron and the nucleus decreases with the increase in the distance of the electron from the centre of the nucleus. Thus the electrons present in the last orbit and last subshells (orbitals) are loosely attached to the nucleus. These orbitals are called valence orbitals and such electrons are called valence electrons,

By applying suitable method, these valence electrons are removed from valence orbitals and made to move in a particular direction or can be made to transfer to another substance.

Frictional Electricity:

Thale’s Experiment:

Around 600 BC (Before Christ), a Greek mathematician Thales discovered that amber (a resinous material) rubbed with animal fur attracted light objects like pieces paper, feathers, and treads.  Both the amber and the fur acquired this property of attracting lighter objects. Amber in the Greek language is called ‘electron’. From this word, Thale coined a word ‘electricity’. Even though other people may have noticed this before, Thales was the first to record his findings. We don’t have his writings, but from other people’s reports of his work, we can guess at his experiments. At this time, magnetism was also confused with static electricity. In this experiment, it is said that the amber and fur have acquired electrical property and process of acquiring electrical property is called electrification.

Explanation:

When a body is rubbed over another, the transfer of valence electrons from one substance to another takes place. The body which loses valence electrons become electron deficient and acquires a positive charge, while the body which gets the electrons becomes electron rich and acquires a negative charge. As the electricity is produced by rubbing (friction), this electricity is called as frictional electricity.

A charge may be defined as the amount of electricity present in a body. S.I. unit of charge is coulomb (C) named after Charles Coulomb. It is a scalar quantity and its dimensions are [L^oM^oA¹T¹].

Gilbert’s Experiment:

In the early sixteenth century, Gilbert performed the similar example as Thales had performed but he used other materials like a glass rod, ebonite rod etc. He also gave characteristics of charges developed on the bodies.

When a glass rod is rubbed with a silk cloth, the loosely attached valence electrons of glass rod get transferred to the silk cloth. Thus in case of glass rod becomes electron deficient and acquires a positive charge, while the silk cloth has the excess of negative charge and acquires a negative charge. The total charge of the system i.e. the glass rod and the silk cloth remains zero.

When an ebonite rod is rubbed with a fur, the loosely attached valence electrons of fur get transferred to the ebonite rod. Thus ebonite rod has e the cess of electrons and acquires a negative charge, while the fur is electron deficient and acquires a positive charge. The total charge of the system i.e. the ebonite rod and the fur remains zero.

Gilbert charged two glass rods and found that the two glass rods repel each other. Then he charged two ebonite rods and found that the two ebonite rods repel each other. From this, he concluded that the like charges repel each other. He charged glass rod and bought a charged ebonite rod near to glass rod, he found that the two rods attract each other. From this, he concluded that the unlike charges attract each other.

Thus there are two types of charges positive and negative. Charge produced on glass rod by rubbing it with a silk cloth is considered as a positive charge, while charge produced on ebonite is considered as a negative charge.

For electrification, two material bodies are involved. The following list gives some objects which are arranged in the order such that if the two objects from the list are rubbed together, they get electrified. The object appearing first in the list acquires a positive charge and the object which appears later in the list acquires a negative charge.

Characteristics of Charges:

• There are two types of charges, namely positive and negative.
• Like charges ( positive and positive or negative and negative) repel each other. Unlike charges (positive and negative) attract each other.

• When neutral body accepts excess of electrons then it acquires a negative charge, while a neutral body loses electrons, then it acquires a positive charge.
• The total charge on a body (either positive or negative) is an integral multiple of the magnitude of the charge on an electron.
• When a glass rod is rubbed with a silk cloth, the glass rod acquires a positive charge and the silk cloth acquires negative charge, but the total charge of the system i.e. combined charge on a glass rod and silk cloth is zero.

• The charge per unit surface area is called surface charge density. It is more at sharp curves and pointed tips. The charge always remains on the outer surface of a conductor. On the uniform surface, it gets distributed uniformly.

• If the charge is produced on insulator, then it remains stationary at the supplied position on the insulator, while if the charge is produced on a conductor, then it gets distributed on the surface of the conductor.
• The charge supplied to a conductor always reside on the outer surface.
• Electrical charge is a scalar quantity.

Experiments to Study Characteristics of Electrical Charges:

Coulomb’s or Biot’s Experiment:

Coulomb demonstrated that charge always resides on the outside surface of a conductor with the aid of two hemispherical cups called Coulomb’s hemispheres which fitted exactly round an insulated metal sphere. These Coulomb’s hemispheres have insulating holders attached to them.

The sphere mounted on the insulated stand is first charged, and afterwards, the hemispheres are fitted over it by holding at insulating handles. On removing the hemispheres they are found to be charged, but the sphere becomes chargeless. This shows that all the charge on the sphere must have passed to the outside of the hemispheres.

Faraday’s Butterfly Net Experiment:

Michael Faraday used an insulated cotton net to act as a hollow conductor. at cone apex of the net, a silk thread is attached which extends on both the sides, pulling which the net surfaces can be turned inside out.

The charge is given to inside surface of the net and it is observed that the charge gets distributed on the outer surface of the net.

Now the string is pulled from the ringside so that the surfaces flip. i.e. the inside surface becomes the outside surface and the outside surface becomes the inside surface. Again charge is found residing on the outer surface.

Atmospheric Electricity:

Benjamin Franklin discovered atmospheric electricity. When he was flying a kite made up of silk cloth and iron wire as the cross of the kite on a rainy day, he got electricity shocks through the silk thread connected to the kite. From this, he concluded that the clouds contain electric charges.

Reason for the Charge on Clouds:

The heat from the sun and hot air causes evaporation of water bodies like the sea, river, etc. to vapourize. These vapours rise to height and get accumulated in the sky. This accumulation of vapour particles is the cause of formation of clouds.

When the molecules of cloud rub with each other, and thus they get charged due to friction. A large amount of electrostatic charge (either positive or negative) gets accumulated on the clouds, resulting in the increase in its electrical potential.

When two clouds of high electrical potential but carrying opposite charges come to each other, the air between them gets ionized and the electrons jump from negatively charged cloud to positively charged cloud. It produces a dazzling white streak of light called the lightning.

During lightning, a large amount of heat is produced, which creates pressure waves, which are transferred in all the directions, and produce a very loud sound called the thunder.

Sometimes during lightning, the accumulated charge on clouds tends to conduct to the surface of the earth. It is to be noted that the charge ties to strikes a conductor that is very near to it like tall buildings and trees. A negatively charged cloud induces a positive charge at the top of the building and a negative charge at its base. Thus a potential difference is created between the top and base of the building. During the rain, the moist air creates a path between the cloud and the top of the building creating a path for the flow of the charge. When the electrons from the cloud reach the top of the building a very high current is set between the top of the building towards the base, which may cause a fire to the building. Thus lightning can have a very devastating effect. To protect high rise buildings from this destruction a lightning rod is put at the top of the building which is connected to the earth. Thus now the electrical current has the easy path through the lightning rod. When a charge is received it is passed to the ground through the lightning rod and not through building itself. Thus the building is safeguarded from the devastating effect of the lightning.

Science > Physics > Electrostatics > Introduction to Static Electricity

The post Introduction to Static Electricity appeared first on The Fact Factor.

In this article, we shall study the concept of quantization of electric charge and the principle of conservation of electric charges.

The fact that all observable charges are always some integral multiple of elementary charge e = 1.6 × 10^-19 C is known as quantization of electric charge.

Thus q = ± ne, where n = 1, 2, 3, …..

e = 1.6 × 10^-19 C is the magnitude of the lowest possible charge which is carried by an electron and proton. The cause of the quantization of electric charge is due to the fact that when one body is rubbed with the other, an integral number of electrons are transferred. There is no scientific explanation for quantization of electric charge in electrodynamics theory and modern physics but it can be verified experimentally.

At the microscopic level, Gell-Mann and Zweig postulated that all elementary particles are built out of more elementary constituents called quarks. Protons and neutrons are made up of two types of quarks i) up quarks denoted by ‘u’ carrying charge +2e/3 and ii) down quarks denoted by ‘d’ carrying charge – e/3. According to quark model the composition of proton is (uud) carrying charge (2e/3 +2e/3 – e/3 = e) and that of neutron is (udd) carrying charge (2e/3 – e/3 – e/3 = 0). Till now the existence of quarks is not detected experimentally but their existence is proved indirectly. In future when they are detected experimentally only we have to change the definition of quantization from e to e/3. The idea of quantization will remain the same.

Coulomb is not a Practical Unit or it is Very Large Unit:

Let us consider a body giving 1 billion (10⁹) electrons per second. Let us calculate the time to create a charge of 1 C

We have q = ne

∴ Number of electrons required = n = q/e = 1/1.6 × 10^-19 = 6.25 × 10¹⁸

Time for obtaining these electrons = t = 6.25 × 10¹⁸/ 10⁹

= 6.25 × 10⁹ seconds =  6.25 × 10⁹/ (365 × 24 × 60 × 60) = 198.2 years

This indicates that the coulomb is a very large unit, hence practical units like milicoulomb (mC), microcoulomb(μC), nanocoulomb (nC) are used.

Principle of Conservation of Charges:

Electric charge can neither be created nor be destroyed but it is transferred from one part of a system to another part of the system so that the total charge of an isolated system remains constant.

Illustration – 1:

When a glass rod (electrically neutral) is rubbed with a silk cloth (electrically neutral), the loosely attached valence electrons of the glass rod get transferred to the silk cloth. Thus in case of glass rod becomes electron-deficient and acquires a positive charge, while the silk cloth has the excess of negative charge and acquires a negative charge. The total charge of the system i.e. the glass rod and the silk cloth remains zero.

Illustration – 2:

When a γ ray photon having energy equal or greater than 1.01 MeV passes near very close to the nucleus, the electric field created by the nucleus would annihilate γ rays photon and create a pair of an electron and positron. This phenomenon is known as pair production. It is represented as

γ   → e^–   +  e⁺

We can see that the total charge on either side is equal (zero)

Illustration – 3:

When electron and positron come very close to each other, they disappear forming two γ ray photons each of energy o.51 MeV. This phenomenon is known as annihilation of matter. It is represented as

e^–  + e ⁺  →  γ   +   γ

We can see that the total charge on either side is equal (zero)

Illustration – 4:

Consider the following reaction showing α decay of uranium.

₉₂U²³⁸  →  ₉₀U²³⁴  +  ₂He⁴

We can see that the total charge on either side is equal (+ 92e)

Illustration – 5: 

Consider nuclear fission reaction

₉₂U²³⁵  +  ₀n¹  → ₁₅₆Ba¹⁴¹  +  ₃₆Kr⁹²   + 3 ₀n¹ + Energy

We can see that the total charge on either side is equal (+ 92e)

Electric charges have additive nature. The total electric charge on a body is equal to the algebraic sum of all the electric charges located anywhere on the body. When doing the algebraic sum due importance should be given to the sign (positive or negative) should be given.

Numerical Problems:

Example – 01:

How much electronic charge is required to make 1 coulomb.

Given: Total charge = q = 1 C, Electronic charge = e = 1.6 × 10^-19 C

To find: Number of electronic charge = n =?

Solution:

We have q = ne

∴ n = q/e = 1/1.6 × 10^-19 = 6.25 × 10¹⁸

Ans: Number of electronic charge is 6.25 × 10¹⁸

Example – 02:

How many electrons should be removed from a conductor so that it acquires a positive charge of 3.5 μC.

Given: Total charge = q = 3.5 μC = 3.5 × 10^-6 C, Magnitude of the charge on electron = e = 1.6 × 10^-19 C

To find: Number of electrons removed = n =?

Solution:

We have q = ne

∴ n = q/e = 3.5 × 10^-6/1.6 × 10^-19 = 2.1875 × 10¹³

Ans: Number of electrons removed is 2.1875 × 10¹³

Example – 03:

Calculate the positive charge and negative charge on the water in a cup holding 250 g of water.

Given: Mass of water

To find: Number of electrons = n =?

Solution:

The molecular formula for water is H₂O. Its molecular mass is 18 g mol^-1

Number of Moles of water = Given mass/molecular mass = 250 /18 = 13.89

1 mol of   water contains 6.022 × 10²³ molecules of water

Number of molecules in 13.89 moles of water = 13.89 × 6.022 × 10²³

Number of molecules in 13.89 moles of water = 83.66 × 10²³

Each molecule of water contains 2 hydrogens (1 electron each) and 1 oxygen (8 electrons)

Number of electrons in each water molecule = 1 × 2 + 8 × 1 = 10

Total number of electrons in a cup = 83.66 × 10²³ × 10 = 83.66 × 10²⁴

Total negative charge on water = 83.66 × 10²⁴ × 1.6 × 10^-19 =1.34 × 10⁷ C

As water is electrically neutral, total positive charge=1.34 × 10⁷ C

Ans: The total negative charge is – 1.34 × 10⁷ C and the total positive charge is + 1.34  × 10⁷ C

Example – 04:

Find the number of electrons moving through an electric bulb per second, rated with power 100 W at 230 V.

Given: Power of bulb = P = 100 W, Voltage = V = 230 V

To find: Number of electrons passed = n =?

Solution:

P = VI =V q/t

∴ q = P t /V = (100 × 1)/230 = 0.4348 C

∴ n = q/e = 0.4348/1.6 × 10^-19 = 2.72 × 10¹⁸

Ans: Number of electrons passed is 2.72 × 10¹⁸

Example – 05:

Two identical spheres carrying charges -2 μC and 14 μC are made to contact each other and then separated. Find charge on each sphere after separation

Given: Charge on first sphere q₁ = -2 μC, Charge on the second sphere = q₂ = 14 μC

To find: Charge on each sphere =?

Solution:

Total charge on the system = -2 + 14 = 12 μC

As the two spheres are identical the charge will get equally distributed among them

Hence charge on each sphere = 12/2 =6 μC

Science > Physics > Electrostatics > Quantization of Electric Charge

The post Quantization of Electric Charge appeared first on The Fact Factor.

In this article, we shall study methods of charging of body and different apparatus used for detection of charge on the body.

Charging of Body:

Charging by Friction:

When a body is rubbed to another, there is a transfer of electrons from one body to another due to friction.  The body losing electrons is positively charged and the body gaining electrons is negatively charged. The amount of gained and the lost electrons is equal to each other. Hence the total charge of the system is conserved.

When a glass rod is rubbed with a silk cloth, the glass loses electrons and gets positively charged while the silk cloth gains electrons and gets negatively charged.

Charge Producers:

The charge producers consist of two wands, one with dark coloured material and one with white coloured material attached to a conductive disk. After rubbing the dark and white surfaces of the two charge producers together. The disk with the white surface will acquire a positive charge; the disk with the dark surface will acquire a negative charge.

Charging by Conduction:

In the electrically neutral body, there are equal numbers of electrons and protons. The body can be charged by changing this balance by some external agency.

When a negatively charged rod touches the neutral body mounted on an insulating stand, then some of the electrons from the rod pass to the neutral body. As a result, the neutral body is negatively charged by contact due to the conduction of electrons from the negatively charged rod to the neutral body.

If the rod is positively charged, then some of the electrons from the neutral body pass to the rod and the neutral body becomes electron-deficient and acquires a positive charge by contact due to the conduction of electrons from the neutral body to the positively charged rod.

When a charged object touches to a neutral object, they both have the same charge. after contact, they start repelling each other due to the same nature of the charge. When two charged bodies touch each other, the total charge of the system is conserved and they share the total charge according to their capacities.

Charging by Induction:

Conductors can also be charged without contact. Let us consider a negatively charged rod is brought near (without contact) a neutral body mounted on an insulating stand, which is a good conductor of electricity. The rod repels the electrons in the conductors. Hence electrons move towards the far end and protons stay at near end Thus, the near end acquires positive charge while the far end acquires a negative charge. The total charge is zero. Now the far end is grounded. The negative charge on the far end is a free charge it moves towards the earth, while the positive charge is a bound charge remains on the body. Now earthing is removed at the negatively charged rod moved away, the body retains the positive charge.

Let us consider a positively charged rod is brought near (without contact) a neutral body mounted on an insulating stand, which is a good conductor of electricity.The rod attracts the electrons in the conductors. Hence electrons move towards the near end and protons stay at the far end Thus, the near end acquires negative charge while the far end acquires a positive charge. The total charge is zero. Now the far end is grounded. The positive charge on the far end is a free charge it is neutralized, while the negative charge is a bound charge remains on the body. Now earthing is removed at the negatively charged rod moved away, the body retains the negative charge.

Detection of Charge on a Body:

Proof Plane:

A proof plane is used for detection of charge. If the size of a body to be tested is very large, then an instrument called proof plane is used. The proof plane is brass or an aluminium-covered conductive disk attached to an insulated handle. It is used to carry the sample of the charge on charged conductive surfaces to transfer to the electroscope.

To collect a sample, the proof plane is rested on the surface of a charged body. When the proof plane is detached it carries the same nature of charge as that carried by the charged body.

Gold Leaf Electroscope:

This instrument is used for the detection of charge and measuring static electricity. It works on the principle that the like charges repel each other.

It consists of an evacuated glass jar placed on a nonconducting surface like wood. The mouth of the jar is sealed. A brass rod passes through the seal. inside the jar, at the lower end of the brass rod, two flattened gold foils are fixed parallel to each other. Sometimes only one gold foil is fixed and thin brass plate at the lower end of the brass rod acts as a parallel plate. At the bottom and lower lateral sides of the jar, tin foils are fixed (optional), which help the gold foils to retain their charge for a longer time.  A brass disc is provided at the top of the brass rod.

When a charge is put on the disc at the top it spreads down to the plate and the gold leaves. Now both the leaves and plate will have the same charge. Similar charges repel each other and hence the leaves diverge from each other. Bigger the charge the more is the divergence of the leaves.

After the use of electroscope, the gold leaves can be made to come together by touching the disc or earthing the disc of the electroscope.

The electroscope can be charged in two ways: (a) by contact – a charged rod is touched on the surface of the disc and some of the charges are transferred to the electroscope. This is not a very effective method of charging the electroscope. or (b) by induction – a charged rod is brought up to the disc and then the electroscope is earthed, the rod is then removed. The two methods give the gold leaf opposite charges.

Pith Ball Electroscope:

A pith ball electroscope is a pith ball hanging from a copper hook by help pf a silk thread. It is used to test whether an object is charged or not.

When a non-charged object is brought near a non-charged pith ball electroscope, the pith ball will not move. If the object is charged then the pith ball will move towards the charged object because it is attracted to it.  Now both the pith ball and charged object has same nature of charge hence the pith ball moves away from the charged object. Now if the oppositely charged body is brought near the pith ball it gets attracted. The extent of repulsion or attraction depends on the strength of a charge on the charged body.

Science > Physics > Electrostatics > Charging a Body and Detection of Charge

The post Charging a Body and Detection of Charge appeared first on The Fact Factor.

On the basis of electrical conductivity, substances can be classified into three types conductors, insulators, and semiconductors. In this article, we shall have a brief idea of semiconductors.

Semiconductors are the substances whose conductivity lies between the conductors and insulators e.g. Germanium, Silicon, etc. They are covalent solids. These elements are members of the fourth group of the periodic table with outer orbit configuration ns² np² and valency 4. There are no free electrons for conduction in semiconductors at low temperature (absolute zero). Thus germanium crystal acts as an insulator at absolute zero. As the temperature increases, the energy gap reduces and some electrons jump to the conduction band. Thus the conductivity of semiconductors increases with the increase in the temperature. Such semiconductors are also called as extrinsic or pure semiconductors. The conductivity of semiconductors can be increased by purposely adding pentavalent or trivalent impurity (doping) to their crystal in small traces.

The structure of Pure Silicon (Semiconductor) Crystal:

We can see that each silicon atom share its four valence electrons with neighbouring 4 silicon atoms to form four covalent bonds. Thus at absolute zero, all the electrons are localized and not available for conduction. Thus at absolute zero silicon behaves as an insulator.

Types of Semiconductors:

Depending upon the working semiconductors are classified into two types.

Intrinsic semiconductors:

A semiconductor which is in extremely pure form is called intrinsic semiconductor e.g. Germanium, Silicon. The crystal structure of these elements consists of regular repetition in three dimensions of a unit cell having the form of a tetrahedron, with one atom at each vertex. 3. The two-dimensional representation is as shown below.

Consider a semiconductor like germanium having valency four. Germanium atom has four electrons in its outermost shell. Germanium has a crystalline structure in which each atom of germanium shares its valence electrons with four neighboring atoms forming four covalent bonds. The covalent bonds are strong bonds. Thus there is no free electron for conduction in germanium at low temperature (absolute zero). Thus germanium crystal acts as an insulator at absolute zero.

At room temperature, the thermal energy of some electrons increases and they are set free. These free electrons get delocalized and are available for conduction. When these electrons get delocalized, a hole is created at their position. Thus the crystal shows a small conductivity.

Extrinsic semiconductors:

The crystal of intrinsic semiconductors shows a small conductivity. The conductivity of semiconductors can be increased by adding a small quantity of some impurity in the pure crystal of the semiconductor. This process is called doping. The ratio of impurity is very low i.e. 1 atom of impurity for every 10⁶ to 10¹⁰ atoms of semiconductors. These atoms of impurities are so less that they do not affect the crystal structure of the semiconductor. Generally, trivalent or tetravalent elements are added as impurities to semiconductor crystal. Depending upon the impurity the semiconductors are classified into two types a) p-type semiconductor and b) n-type semiconductor

p-type Semiconductor:

Let us suppose the germanium is doped with an element from the third group say boron (trivalent impurity). Boron has three Valency electrons. Therefore, boron can form only three covalent bonds with neighboring germanium atoms. One of the covalent bonds around each boron atom has an electron missing. The absence of an electron is called a hole. This impurity is called acceptor impurity.

Under the action of an electric field, an electron from a neighboring completely filled covalent bond jumps into this hole creating a hole in the bond from which electron has moved. The process is repeated continuously. Thus the hole appears to move through the crystal from a positive end to a negative end. Thus the conductivity of doped germanium increases. The absence of an electron in the hole means the presence of a positive charge. Hence the doped material is called p-type semiconductor.

Characteristics of p-type Semiconductors:

• In p-type semiconductors, doping is done with trivalent impurity i.e. impurity from the third group of the periodic table.
• The impurity in the p-type semiconductor is called the acceptor impurity.
• Each atom of impurity creates a hole in the crystal.
• The electrical conductivity is due to the hole.
• When a potential difference is applied across the p-type of semiconductor, the holes appear to move from a positive end to a negative end.
• In p-type semiconductors, holes are the major charge carriers.

n-type Semiconductors:

Let us suppose the germanium is doped with an element from the fifth group say phosphorous (pentavalent impurity). Phosphorus has five valence electrons. Therefore, phosphorus can form four covalent bonds leaving one free electron unbonded. Due to pentavalent doping the number of free electrons increases. This impurity is called the donor impurity.

Under the action of an electric field, free-electron around phosphorous moves through the crystal from the negative end to a positive end. Thus the conductivity of doped germanium increases. The presence of an electron means the presence of a negative charge. Hence the doped material is called an n-type semiconductor.

Characteristics of n-type Semiconductors:

• In n-type semiconductors, doping is done with pentavalent impurity i.e. impurity from the fifth group of the periodic table.
• The impurity in the n-type semiconductor is called the donor impurity.
• Each atom of impurity leaves one free electron in the crystal.
• The electrical conductivity is due to electron set free by the electron.
• When a potential difference is applied across n-type of semiconductor, the electrons move from a negative end to a positive end.
• In n-type semiconductors, electrons are the major charge carriers.

Uses of Semiconductors:

• Various combinations of n-type and p-type semiconductors are used for making electronic components.
• A diode is a combination of n-type and p-type semiconductors and is used as a rectifier.
• Transistors are made by sandwiching a layer of one type of semiconductor between two layers of the other type of semiconductor. NPN and PNP types of transistors are used to detect or amplify radio or audio signals.
• The solar cell is an efficient photodiode used for the conversion of light energy into electrical energy. It consists of both p-type and n-type semiconductors.

Science > Chemistry > Solid State > Semiconductors

The post Semiconductors appeared first on The Fact Factor.

In the last article, we have studied the dielectric properties of solids. In this article, we shall study the electrical properties of solids.

Electrical Conductivity:

The electrical conductivity of solids is due to the motion of electron or positive holes. The conductivity due to the motion of electron or positive holes is called electronic conductivity. The electrical conductivity may be due to the motion of ions. The conductivity due to the motion of ions is called ionic conductivity. Conductivity due to electrons is called n-type conductivity while that due to holes is called p-type conductivity.

In metals, electrical conductivity is due to the motion of electrons and the electrical conductivity increases with the increase in the electrons available for conduction, the electrical conductivity increases. In pure ionic solids, ions are not available for conduction hence in the pure solid state they are insulators. Due to the presence of defects in the crystal electrical conductivity increases.

Solids exhibit a varying range of electrical conductivities, extending of magnitude ranging from 10^–20 to 10⁷ ohm^–1 m^–1. Solids can be classified into three types on the basis of their conductivities. The difference in conductivities of conductors, insulators, and semiconductors can be explained on the basis of band theory.

Electrical Conductivity on the Basis of Energy Bands:

The group of discrete but closely spaced energy levels for the orbital electrons in a particular orbit is called energy band. Inside the crystal, each electron has a unique position and no two electrons see exactly the same pattern of surrounding charges. Because of this, each electron will have a different energy level. These different energy levels with continuous energy variation form what are called energy bands.

The energy band which includes the energy levels of the valence electrons is called the valence band. The energy band above the valence band is called the conduction band. With no external energy, all the valence electrons will reside in the valence band.

On the basis of energy bands and electrical conductivity, solids can be classified as:

Conductors:

The solids with conductivities ranging between 10⁴ to 10⁷ ohm^–1 m^–1 are called conductors. Metals have conductivities in the order of 10⁷ ohm^–1 m^–1 are good conductors. In conductors, the lowest level in the conduction band happens to be lower than the highest level of the valence band and hence the conduction band and the valence band overlap. Hence the electron in the valence band can migrate very easily into the conduction band. Thus at room temperature, a large number of electrons are available for conduction. Examples: Copper, Aluminium, Silver, Gold, All metals

Characteristics of Conductors:

• The substances which conduct electricity through them to a greater extent are called conductors.
• In conductors, the conduction band and valence band overlap with each other or the gap between them is very small.
• There are free electrons in the conduction band.
• Due to increase in temperature conductance decreases.
• There is no effect of the addition of impurities on the conductivity of conductors.
• Their conductivity ranges between 10⁴ to 10⁷ ohm^–1 m^–1.

Conduction in Metallic Solids:

A metal conductor conducts electricity through the movement of free electrons. Metals conduct electricity in solid as well as a molten state. The conduction of electricity is due to the transfer of electrons and not due to the transfer of matter. The conductivity of metals depends upon the number of valence electrons available per atom. It is nearly independent of the presence of impurity and lattice defects. Conductivity decreases with the increase in the temperature. It can be explained as follows

M → Mⁿ⁺_kernel + ne^–  free electrons

The kernels are fixed. Due to the increase in temperature, the amplitude of vibration of kernels increases. Hence the obstruction to the flow of electron increases.

Insulators :

These are the solids with very low conductivities ranging between 10^–20 to 10^–10 ohm^–1 m^–1. The conduction band and valence band are widely spaced. Thus forbidden energy gap between the valence band and conduction band is large (greater than 3 eV). Hence the electron in the valence band cannot migrate into the conduction band. Hence no electrons are available for conduction. But at a higher temperature, some of the electrons from the valence band may gain external energy to cross the gap between the conduction band and the valence band. Then these electrons will move into the conduction band. At the same time, they will create vacant energy levels in the valence band where other valence electrons can move. Thus the process creates the possibility of conduction due to electrons in conduction band as well as due to vacancies in the valence band. Examples: Glass, wood, paper, plastic, mica.

Characteristics of Insulators:

• In Insulators the conduction band and valence band are widely separated.
• There are no free electrons in the conduction band.
• There is an energy gap between the conduction band and the valence band which is more than 3 eV.
• There is no effect of change of temperature on the conductivity of insulators.
• There is no effect of the addition of impurities on the conductivity of insulator.
• They have very low conductivities ranging between 10^–20 to 10^–10 ohm^–1 m^–1.

Semiconductors :

These are the solids with conductivities in the intermediate range from 10^–6 to 10⁴ ohm^–1 m^–1.

The forbidden energy gap between the valence band and conduction band is less than 3 eV. Thus energy gap between the valence band and conduction band is small. At absolute zero, no electrons are available for conduction.

As the temperature increases, many electrons from the valence band may gain external energy to cross the gap between the conduction band and the valence band. Then these electrons will move into the conduction band. At the same time, they will create vacant energy levels in the valence band where other valence electrons can move. Thus the process creates the possibility of conduction due to electrons in conduction band as well as due to vacancies in the valence band. Examples: Silicon, Germanium

Characteristics of Semiconductors:

• In semiconductors, the conduction band and valence band are very close to each other or the forbidden energy gap between them is very small.
• The electrons of the valence bond can easily be excited to the conduction band.
• There is an energy gap between the conduction band and valence band which is less than 3 eV.
• Due to increase in temperature conductance increases.
• There is an effect of the addition of impurities on the conductivity of semiconductors.
• Their conductivity ranges from 10^–6 to 10⁴ ohm^–1 m^–1.

Science > Chemistry > Solid State > Electrical Properties of Solids

The post Electrical Properties of Solids appeared first on The Fact Factor.

1.1.1.1 What is Physics?

Science word is derived from the Latin word ‘Scientia’ which means ‘to know’. Science has many disciplines, Physics being one of them. The word Physics is derived from the Greek word ‘Fusis’ meaning ‘nature’. Physics is that branch of Science which deals with the study of matter and energy or matter or motion i.e. Physics is a study of matter and energy in its different forms. In other words, physics is the study of nature and its laws. We expect that all the different events taking place in nature always take place according to some basic rules and revealing these rules of nature from the observed events in physics.

As physics is a study of nature and its behaviour it is real science. No one has been given authority to frame the rules. Sir Issac Newton, Einstein are the great physicist because using the observations available at that time, they could guess and frame the laws of physics, which explain these events and the observations in a convincing way. If a new phenomenon is observed which can not be explained using existing laws or rules we are always free to change the rules.

Knowledge of Physics overlaps with other sciences considerably, hence such overlapping gives rise to subjects like Biophysics, Biochemistry, Astrophysics, Geophysics, etc.

Physics can be conveniently divided into two parts, classical Physics (Pre-1900) and modern Physics (Post – 1900). Classical physics includes the study of mechanics, gravitation, heat, sound, light, electricity and magnetism. Modern Physics includes the study of quantum mechanics, relativity, atoms, molecules, nuclei, elementary particles, and condensed matter.

The complex physical phenomena involving wide range of length, mass. and time can be easily understood due to following reasons:

• A quantitative study of various natural phenomena shows that there is some regularity and symmetry even in the most complex phenomenon which helps us to understand it.
• All these phenomena can be explained in terms of only a few basic laws.
• Complex phenomena can be separated into simpler phenomena and by understanding these simple phenomena, the complex phenomena can be understood.

Scientific Methods:

The study of science and particularly in Physics is based on systematic observation, logical reasoning, model making, and theoretical prediction and necessary modifications. All the four steps taken together constitute what we call the ‘scientific method’. The scientific method helps us to describe the given physical phenomenon or behavior of a physical system in terms of a limited number of laws. This gives us what we call ‘theory’. The theory should be self-consistent and consistent with known experimental data. The discrepancy between the theory and experimental data has to lead to new theories in Physics.

Relation Between Physics and Mathematics:

Physics is directly related to maths because the description of nature becomes easy if we have the freedom to use mathematics. In physics, we use mathematical techniques like algebra, trigonometry, and calculus. Thus mathematics is a language of physics. Without knowledge of mathematics, it would be much more difficult to discover, understand and explain the laws of nature. But we should note that mathematics itself is not physics. To understand nature is a journey of physics, mathematics is the mean of the journey.

Back to List of Sub-Topics

1.1.1.2 Scope of Physics:

The scope of physics is broad and encompasses the study of the fundamental principles governing the natural world. Physics not only explores the properties and behaviour of matter and energy but also plays a crucial role in advancing technology, contributing to other scientific disciplines, and addressing fundamental questions about the nature of the universe. Here are key aspects of the scope of physics:

Mechanics:

Mechanics is a branch of physics, which deals with the motion of material bodies. In this branch, the forces responsible for producing or changing the motion of the body are studied. The energy involved is also studied. Newton’s laws of motion, the law of conservation of momentum and energy, Newton’s gravitation law forms the base of this branch of Physics.

Heat:

Heat is the energy that a body possesses by virtue of the motion of the molecules of which it is composed and the potential energy due to interatomic forces. The term heat is also used to indicate the energy in the process of transfer between an object and its surroundings because a difference exists between their temperatures. Thermodynamics is the name given to the branch of physics which studies the relationship between heat and mechanics.

Acoustics:

Acoustic is a branch which studies sound. Wave motion is studied in this branch.  An object in a state of vibration can set medium particles in the vibration and this disturbance in the medium can travel from one point to another. Thus sound is wave motion itself.

Optics:

Optics is a branch of science which studies electromagnetic waves to which the eye responds (light). Propagation of light means the propagation of electromagnetic waves with varying electric and magnetic fields through a vacuum or a transparent medium. It has two broad branches: geometric optics and physical optics.

Electricity and Magnetism:

These topics are interrelated with each other. We have to take the help of another topic when we are studying one of them individually. Electricity deals with the forces on charged particles, the effect of such forces. It also studies the phenomenon caused by the motion of charged particles. Magnetism can have an effect on the electric current. magnetic materials can be used in producing electric currents. Electronics is the branch of electricity.

Modern Physics:

Modern physics is the branch of physics which deals with the recent developments in the science-related to physics such as Radioactivity, X-Rays, Cathode Rays, Atomic and Molecular Structure, Quantum Theory and wave mechanics, etc.

Back to List of Sub-Topics

1.1.1.3 Pioneers of Physics

Back to List of Sub-Topics

1.1.1.4 Click Here to find the List of Noble Prize Winners in Physics

Conclusion:

Physics is a branch of science that seeks to understand the fundamental principles governing the natural world, encompassing everything from the smallest particles to the largest galaxies. It involves the study of matter, energy, space, and time, as well as the interactions between these elements. Physicists explore the fundamental laws and forces that govern the behaviour of the universe and seek to explain and predict the observed phenomena. Physics relies heavily on mathematical models and experimental observations. The scientific method is a fundamental aspect of physics, involving the formulation of hypotheses, experimentation, and the development of theories that can be tested and refined through further observations and experiments.

Related Topics:

• 1.1.2 Scientific Methods
• 1.1.3 Scientific View
• 1.1.4 Physics and Other Sciences

For More Topics in Physics Click Here

The post 1.1.1 Introduction to Physics appeared first on The Fact Factor.