Internet and Its Services
The Internet has gained popularity and emerged as an important and efficient means of communication. The idea of introducing the Internet was to allow millions of people to share information and ideas, sound, video clips using their computers across the world. The Internet is a worldwide network of networked computers those are able to exchange information with each other. It consists of thousands of separately administered network of various sizes and types.
Internet
Internet stands for International Network, which began in 1950's by Vint Cerf known as the 'Father of Internet. Internet is a 'network of networks' that consists millions of private and public networks of local to global scope. Basically, network is a group of two or more computer systems linked together.
The data move around the Internet is controlled by protocols. Under TCP/IP protocol (Transmission Control Protocol/Internet Protocol), a file is broken into smaller parts by the file server called packets. All computers on the Internet, communicate with one another using TCP/IP, which is a basic protocol of the Internet.
History of Internet
In 1969, the University of California at Los Angeles, the University of Utah were connected as the beginning of the ARPANET (Advanced Research Projects Agency Network) using 50 kbits circuits. It was the world's first operational packet switching network. The goal of this project was to connect computers at different universities and U.S. defence.
In mid 80's another federal agency, the National Science Foundation, created a new high capacity network called NSFnet, which was more capable than ARPANET. The only drawback of NSFnet was that it allowed only the academic research on its network and not any kind of private business on it. So, private organisations and people started working to build their own networks, which were later interconnected with ARPANET and NSFnet to form the Internet.
Advantages of the Internet
(i) Allows you to easily communicate with other people.
(ii) Global reach enables one to connect anyone on the Internet.
(iii) Publishing documents on the Internet saves paper.
(iv) A valuable resource for companies to advertise and conduct business.
(v) Greater access to information reduces research times.
Disadvantages of the Internet
(i) It is a major source of computer viruses.
(ii)Messages sent across the Internet can be easily intercepted and are open to abuse by others.
(iii) Much of the information is not checked and may be incorrect or irrelevant.
(iv) Unsuitable and undesirable material available that sometimes are used by notorious people such as terrorists.
(v) Cyber frauds may take place involving Credit/Debit card numbers and details.
Internet Connections
Bandwidth and cost are the two factors that help you in deciding which Internet connection is to use. The speed of Internet access depends on the bandwidth.
Some of the Internet connections available for Internet access are as follows
Dial-Up Connection
A Dial-up is a method of connecting to the Internet using more...
Computer Security
Computer security is also known as cyber security or IT security. Computer security is a branch of information technology known as information security, which is intended to protect computers. It is the protection of computing systems and the data that they store or access.
Methods to Provide Protection
There are four primary methods to provide protection
System Access Control It ensures that unauthorised users do not get into the system by encouraging authorised users to be security conscious.
Data Access Control It monitors who can access what data, and for what purpose. Your system might support mandatory access controls with these. The sytem determines access rules based on the security levels of the people, the files, and the other objects in your system.
System and Security Administration It performs offline procedures that makes or breaks secure system.
System Design It takes advantage of basic hardware and software security characteristics.
Components of Computer Security
Computer security is associated with many core areas. Basic components of computer security system are
Confidentiality It ensures that data is not accessed by any unauthorised person.
Integrity It ensures that information is not altered by any unauthorised person in such a way that it is not detectable by authorised users.
Authentication It ensures that users are the persons they claim to be.
Access Control It ensures that users access only those resources that they are allowed to access.
Non-Repudiation It ensures that originators of messages cannot deny they are not sender of the message.
Availability It ensures that systems work promptly and service is not denied to authorised users.
Privacy It ensures that individual has the right to use the information and allows another to use that information.
Stenography It is an art of hiding the existance of a message. It aids confidentiality and integrity of the data.
Cryptography It is the science of writing information in a 'hidden' or 'secret' form and is an ancient art. It protects the data in transmit and also the data stored on the disk.
Some terms commonly used in cryptography are
(i) Plain Text It is the original message that is an input.
(ii) Cipher It is a bit-by-bit or character-by character transformation without regard to the meaning of the message.
(iii) Cipher Text It is the coded message or the encrypted data.
(iv) Encryption It is the process of converting plain text to cipher text, using an encryption algorithm.
(v) Decryption It is the reverse of encryption, i.e. converting cipher text to plain text.
Sources of Cyber Attack
The most potent and vulnerable threat of computer users is virus attacks. A computer virus is a small software program that spreads from one computer to another and that interferes with computer operation. It is imperative for every computer user to be aware about the software and programs that can help to protect the personal computers from attacks.
The sources of attack can more...
Those quantities which can describe the laws of physics and possible to measure are called physical quantities. The physical quantities which do not depend upon other physical quantities are called fundamental quantities. In Standard International (S.I.) system the fundamental quantities are mass, length, time, temperature, luminous intensity, electric current and amount of substance. The physical quantities which depend on fundamental quantities are called derived quantities e.g. speed, acceleration, force, etc.
Units
The unit of a physical quantity is the reference standard used to measure it.
Types of Units
Fundamental Units
The units defined for the fundamental quantities are called fundamental or base units.
Fundamental Physical quantity
Mass (M)
Length (L)
Time (T)
Temperature
(\[\theta \]or k)
Electric current (I)
Luminous intensity
Amount of Substance
Fundamental unit
Kilogram (kg)
Meter (m)
Second (s)
Kelvin (k)
Ampere (A)
Candela (cd)
Mole (mol)
Derived Units
The units defined for the derived quantities are called derived units, e.g. unit of speed or velocity (metre per second),
Acceleration (metre per second\[\sec on{{d}^{2}}\]) etc.
Dimensions
The limit of a derived quantity in terms of necessary basic units is called dimensional formula and the raised powers on the basic units are dimensions.
Elasticity and Plasticity
The property of the body to regain its original configuration (length, or shape) when the deforming forces are removed is called elasticity. On the other hand, if the body does not have any tendency to regain its original configuration on removal of deforming force the body is called plastic body and this property is called plasticity.
Perfectly elastic body: A body which regains its original configuration immediately and completely after the removal of deforming force from it, is called perfectly elastic body. Quartz and phosphor bronze, are closed to perfectly plastic body.
Perfectly plastic body: A body which does not regain its original configuration at all on the removal of deforming force, however small the deforming force may be is called perfectly plastic body. Putty mid mud are closed to perfectly plastic body.
Stress
The internal restoring force acting per unit area of a body is called stress. i.e., Stress = Restoring force/Area
Strain
The ratio of change in configuration to the original configuration is called strain.
\[strain=\frac{Change\,in\,\,configuration}{Original\,Configuration}\]
Strain being the ratio of two like quantities has no units and dimensions.
Elastic Limit
Elastic limit is the upper limit of deforming force up to which, if deforming force is removed, the body regains its original form completely and beyond which, if deforming force is increased, the body loses its property of elasticity and gets permanently deformed.
Hooke's low
It states that within the elastic limit stress is directly proportional to strain.
i.e.. Stress \[\propto \]strain or Stress =\[E\times \] strain
Stress or \[\frac{Stress}{strain}=E=Cons\tan t\]
Here E is the coefficient of proportionality and is called modulus of elasticity or coefficient of elasticity of a body:
Materials-Ductile, Brittle and Elastomers
(i) Ductile materials: The materials which have large range of plastic extension are called ductile materials. They can be drawn into thin wires, e.g., copper, silver, aluminium, iron, etc.
(ii) Brittle materials: The materials which have very small range of plastic extension are called brittle materials. These materials break as soon as the stress is increased beyond the elastic limit, e.g., glass, ceramics, cast iron, etc.
(iii) Elastomers: The materials which can be stretched to large values of strain are called elastomers. e.g., rubber, elastic tissue of aorta, etc.
Young's modulus of elasticity (Y): It is defined as the ratio of normal stress to the longitudinal strain within the elastic limit. Thus, \[Y=\frac{Normal\,Stress}{Longitudinal\,Strain}\] or, \[Y=\frac{F/\pi {{r}^{2}}}{\Delta l/{{L}_{0}}}=\frac{Mg{{L}_{0}}}{\pi {{r}^{2}}\Delta l}\]
Thermal Stress
When a rod is rigidly fixed at its two ends and its temperature is changed, then a thermal stress is set up in the rod. And the corresponding strain developed is called thermal strain, Thermal stress \[=\frac{Force}{Area\,\,of\,\,cross\,\,\sec tion}=\frac{F}{A}=Y\alpha \Delta \theta \] Area of cross section A where \[\alpha \] = coefficient of linear expansion of the rod \[\Delta \theta \] = change in temperature. more...
Temperature is defined as the degree of hotness or coldness of a body. It is a scalar quantity Its S.I. unit is kelvin (K). Heat is a form of energy -which causes sensation of hotness or coldness. The flow of heat is always from higher temperature to lower temperature. No heat flows from one body to other, when both the bodies are at the same temperature. The two bodies are said to be in thermal equilibrium. The SI unit of heat is joule. Its CGS unit is calorie, 1 cal = 4.2 joule
Measurement of Temperature
A branch of science which deals with the measurement of temperature of a substance is called thermometry. Thermometer is a device used to measure the temperature. Thermometer used for measuring very high temperatures are called pyrometer.
Relationship between Different Scales of Temperature
\[\frac{C-0}{100}=\frac{F-32}{212-32}=\frac{K-273.16}{373.16-273.16}\]=\[\frac{R-0}{80-0}=\frac{Ra-460}{672-460}\]\[{{T}^{0}}(K)=({{t}^{0}}C+273.16)\] Normal temperature of human body is 310.15 K\[({{37}^{0}}C={{98.6}^{0}}F)\] STP or NTP implies 273.15 K \[({{0}^{0}}C={{32}^{0}}F)\]
Ideal-gas Equation and Absolute Temperature
The equation, PV= nRT where, n = number of moles in the sample of gas R = universal gas constant; (its value is 8.31\[J\,mo{{l}^{-1}}{{K}^{-1}}\]), is known as ideal-gas equation. It is the combination of following three laws
(i) Boyle's law: When temperature is held constant, the pressure is inversely proportional to volume. i.e., \[P\propto \frac{1}{V}\](at constant temperature)
(ii) Charters law: When the pressure is held constant, the volume of the gas is directly porportional to the absolute temperature. i.e., \[V\propto T\](at constant pressure)
(iii) Avogadro's law: When the pressure and temperature are kept constant, the volume is directly proportional to the number of moles of the ideal gas in the container. i.e., \[V\propto n\](at constant pressure and temperature)
Absolute Temperature
The lowest temperature of\[-\,273.16{}^\circ C\] at which a gas is supposed to have zero volume and zero pressure and at which entire molecular motion stops is called absolute zero temperature. A new scale of temperature starting with \[-273.16{}^\circ C\]by Lord Kelvin as zero. This is called Kelvin scale or absolute scale of temperature. \[T\left( K \right)=t{}^\circ C+273.16\]
Thermal Expansion
The increase in the dimensions of a body due to the increase in its temperature is called thermal expansion.
Linear expansion: The fractional increase in length per \[{}^\circ C\] rise in temperature is called coefficient of linear expansion. Coefficient of linear expansion, \[\alpha =\frac{\left( \frac{\Delta \ell }{\ell } \right)}{\Delta T}=\frac{d\ell }{\ell dT}\]
Superficial expansion: On increasing the temperature of a solid, its area increases. This increase in area is referred as superficial expansion. Coefficient a/superficial expansion is defined as the fractional increase in area per \[{}^\circ C\]rise in temperature. i.e., Coefficient of a real expansion \[\beta =\frac{\Delta A/A}{\Delta T}=\frac{dA}{AdT}\]
Cubical expansion: On increasing the temperature of a solid, its volume increases. This increase in volume with increase in temperature is called cubical more...
Any motion that repeats itself in equal intervals of time is called periodic motion. Aperiodic motion can be represented in terms of sines and cosines, so it is called a harmonic motion. The uniformly rotating earth represents a periodic motion that repeats itself at every 24 hours.
Simple Harmonic Motion (S.H.M.)
Oscillatory motion in which the acceleration of the particle is directly proportional to the displacement and directs towards a fixed point in a direction opposite to displacement is called simple harmonic motion abbreviated as S.H.M. If a particle performs oscillatory motion such that its acceleration (a) and displacement (x) are related as below\[a\propto -x\], then the motion of particle is simple harmonic. An oscillatory motion is always periodic but a periodic motion may not be oscillatory.
Examples of S.H.M.
(i) clock pendulum,
(ii) oscillating liquid in a U-tube,
(iii) oscillating block in a liquid,
(iv) oscillating frictionless piston fitted in a cylinder filled with ideal gas, etc.
Sound
Sound is a form of energy which produces a sensation of hearing in our ears.
Source of Sound and its Propagation
A source of vibration (vibration means a kind of rapid to and fro motion of an object) is normally a source of sound. When we pluck a string of guitar or sitar or veena it produces sound. Similarly vibrations of wings of bee or mosquito. Sound is emitted by vibrating source and is transmitted through a material medium producing sensation of hearing in our ears. The motion of a vibrating source sets up waves in the surrounding medium.
Sound Needs a Material Medium for its Propagation
In the absence of medium (air) around the source, sound is not being propagated and light (electromagnetic) waves travel through the vacuum.
Mechanical Waves
A mechanical wave is a periodic disturbance which requires a material medium for its propagation. The properties of these waves depend on the medium so they are known as elastic waves, such as sound-waves, water waves, Waves in stretched string. On the basis of motion of particles the mechanical waves are classified into two parts.
Transverse wave: When the particles of the medium vibrate in a direction perpendicular to the direction of propagation of the wave, the wave is known as the transverse wave. For example, waves produced in a stretched string, waves on the surface. These waves travel inform of crests and troughs. These waves can travel in solids and liquids only.
Longitudinal wave: When the particles of the medium vibrate along the direction of propagation of the wave then the wave is known as the longitudinal wave. For example sound wave in air, waves in a solid rod produced by scrabbing etc. These waves travel in the form of compressions and rarefactions. These waves can travel in solids, liquids more...
The branch of physics which deals with the propagation, nature and behaviour of light is known as optics.
Light
Light is a form of energy -which enables human beings and creatures to 'see' things. When light emitted from an object or reflected from the object enters our eyes we are able to see the object. We can't see an object in dark even if we are in light because there is no light coming from the object to our eyes. Light is an electromagnetic radiation which exhibits properties like a wave as well as a particle. It always propagates in a straight line. Light travels with a speed nearly equal to\[3\times {{10}^{8}}m/s\]According to current theories, no material particle can travel at a speed greater than the speed of light.
Luminous and Non-luminous Objects
Luminous objects are those which emit its own light e.g., sun, glowworm, burning candle, electric lights. Non-luminous objects do not give out its own light but are visible only when light from a luminous object falls on it. e.g., moon, earth, table, paper, etc.
Transparent Translucent and Opaque materials
Transparent materials are those which allow most of light to pass through them. Example: Glass, water, air. Translucent materials allow only a part of light to pass through it. We cannot see distinctly through them. Example: greased paper, Paraffin wax, etc.
Opaque materials: do not allow any light to pass through it. They reflect or absorb all the light that falls on them. Example: Books, desk, stone, rubber, trees, etc.
Reflection of Light
Reflection of Light: When light hits an opaque material, the light may be absorbed by the material and converted into heat energy. If light is not absorbed, it is bounced back or reflected at the surface of material. The turning back of light in the same medium is called reflection of light.
Laws of reflection
The angle of incidence ‘i’ is equal to the angle of reflection ‘r’
At the point of incidence, the incident rays, the normal to the surface and the reflected ray all lie in the same plane.
Reflection by Plane Mirrors
Plane mirror is a looking glass which is highly polished on one surface and is silvered on the other surface. When a light ray strikes the polished surface, it is reflected by the silvered surface. An 'image' is defined as the impression of an object carried over and formed by light reflected from it.
Use of plane mirrors
(a) Plane mirrors are primarily used as looking glasses.
(b) Since, a combination of mirrors can produce multiple images, they are used to provide false dimensions in showrooms.
(c) They are also used as reflectors in solar cookers.
(d) Plane mirrors are used in the construction of a periscope.
Charge is something associated with matter due to which it produces and experiences electric and magnetic effects. The study of charges at rest is called static electricity or electrostatics while the study of charges in motion is called current electricity. There are two types of electric charge:
(i) Positive charge and (ii) Negative charge. The magnitude of elementary positive or negative charge is same and is equal to. \[1.6\times {{10}^{-19}}C\] Charge is a scalar quantity its SI unit is ampere second or coulomb.
Basic Properties of Electric Charge
(1) Similar charges repel and opposite charges attract.
(2) A charged body attracts light uncharged bodies.
(3) Accelerated charge radiates energy.
Conductors and Insulators
The materials which allow electric charge (or electricity) to flow freely through them are called conductors. Metals are very good conductors of electric charge. Silver, copper and aluminium are some of tile good conductors of electricity. The materials which do not allow electric charge to flow through them are called nonconductors or insulators. For example, most plastics, rubber, non-metals (except graphite), dry wood, wax, mica, porcelain, dry air etc., are insulators.
Coulomb's Law
It states that, the electrostatic force of interaction (repulsion or attraction) between two electric charges \[{{q}_{1}}\] and \[{{q}_{2}}\]separated by a distance r, is directly proportional to the product of the charges and inversely proportional to the square of distance between them.
\[F\propto {{q}_{1}}{{q}_{2}}\] and \[F\propto 1/{{r}^{2}}\] or \[F=k\frac{{{q}_{1}}{{q}_{2}}}{{{r}^{2}}}\]
\[K=\frac{1}{4\pi {{\varepsilon }_{0}}}\]\[=9\times {{10}^{9}}\frac{N{{m}^{2}}}{cou{{l}^{2}}}\Rightarrow {{\varepsilon }_{0}}=8.85\times {{10}^{-12}}\frac{cou{{l}^{2}}}{N{{m}^{2}}}\]
Electric Field
Electric Field: The region surrounding an electric charge or a group of charges in which another charge experiences a force of attraction or repulsion is called 'electric field'. \[\overrightarrow{E}=\frac{\overrightarrow{F}}{{{q}_{0}}},\overrightarrow{E}=\underset{{{q}_{0}}\to 0}{\mathop{\lim }}\,\frac{\overrightarrow{F}}{{{q}_{0}}}\] The S.L unit of electric field intensity is N/coul or volt/metre.
Electric Lines of Force
An electric line of force is that imaginary smooth curve drawn in an electric field along which a free isolated unit positive charge moves. Two lines offeree never intersect. If they are assumed to intersect, there will be two directions of electric field at the point of intersection, which is impossible.
Electric Flux ((\[\phi \])
The total number of electric lines of force through a given area is called the electric flux.
(a) For open surface, \[{{\phi }_{0}}=\int{d\phi =\int{\overrightarrow{E}.d\overrightarrow{s}}}\]
(b) For closed surface, \[{{\phi }_{0}}=\oint{\overrightarrow{E}.d\overrightarrow{s}}\]
Gauss's Law
The total electric flux linked with a closed surface is \[\left( \frac{1}{{{\varepsilon }_{0}}} \right)\] times the charge enclosed by the closed surface (Gaussian surface), i.e. \[\oint{\overrightarrow{E}.d\overrightarrow{s}=\frac{q}{{{\varepsilon }_{0}}}}\]
Electrostatic Potential
Potential at a point can be physically interpreted as the work done by the field in displacing a unit + ve charge from some reference point to the given point.
i.e., \[V=\frac{w}{{{q}_{0}}}\]
\[V=-\int\limits_{\infty }^{r}{\overrightarrow{E}.d\overrightarrow{s}}\] i.e. \[E=-\frac{dv}{dr}\] more...
Magnetism
Magnetism: The phenomenon of attracting magnetic substances like iron, cobalt, nickel etc. is called magnetism. A body possessing the property of magnetism is called magnet. Lodestone or magnetite is natural magnet. Earth is also a natural magnet. In magnetized substance all the atomic magnets are aligned in same direction and thus resultant magnetism is non-zero.
Bar Magnet
A bar magnet consists of two equal and opposite magnetic poles separated by a small distance. Poles are not exactly at the ends. The shortest distance between two poles is called effective length (\[{{L}_{e}}\]) and is less than its geometric length (\[{{L}_{g}}\]). For bar magnet \[{{L}_{g}}=2l\]and\[{{L}_{e}}=(5/6){{L}_{g}}\]
Properties of Magnet
(i) Attractive property: When a magnet is dipped into iron fillings it is found that the concentration of iron filings, i.e., attracting power of the magnet is maximum at two points near the ends and minimum at the centre. The places where its attracting power is maximum are called poles.
(ii) Directive property: When a magnet is suspended its length becomes parallel to N-S direction. The pole pointing north is called the north-pole while the other pointing in the geographical south is called the south pole of the magnet. The line joining the two poles of a magnet is called magnetic axis and the vertical plane passing through the axis of a freely suspended or pivoted magnet is called magnetic meridian.
(iii) Poles of a magnet always exist in pairs: In a magnet the two poles are found to be equal in strength and opposite in nature. If a magnet is broken into number of pieces, each piece becomes a magnet with two equal and opposite poles. This shows that monopole do not exist.
(iv) Repulsive property: A pole of a magnet attracts the opposite pole while repels similar pole.
Demagnetisation of Magnet
A magnet gets demagnetised, i.e., loses its power of attraction if it is heated, hammered or alternating current is passed through a wire wound over it.
Permanent and Temporary Magnets (Electromagnets)
The permanent artificial magnets are made of some metals and alloys like Carbon-steel, Alnico, Platinum-cobalt, Alcomax, Ticonal etc. The permanent magnets are made of ferromagnetic substances with large coercivity and retentivity. The temporary artificial magnets like electromagnets are prepared by passing current through coil wound on soft iron core. These cannot retain its strength for a long time. These are made from soft iron, non-metal and alloy. Electromagnets are stronger than permanent magnet.
Some Applications of Electromagnets
(i) Electric motors
(ii) Doorbells
(iii) In scrapyards to separate iron from other metals
Coulomb's Law in Magnetism
If two magnetic poles of strengths \[{{m}_{1}}\] and \[{{m}_{2}}\] are kept at a distance r apart then force of attraction or repulsion between the more...
On the basis of electrical conductivity\[(\sigma )\]or resistivity \[(\rho =1/\sigma )\] the solids are classified as
(i) Metals - have low resistivity
\[\rho \tilde{\ }{{10}^{-2}}\,to\,{{10}^{-8}}\Omega m\],
\[\sigma \tilde{\ }{{10}^{2}}\,to\,{{10}^{8}}S{{m}^{-1}}\]
(ii) Semiconductors - have intermediate resistivity
\[\rho \tilde{\ }{{10}^{5}}\,to\,{{10}^{0}}\Omega {{m}^{{}}}\]
\[\sigma \tilde{\ }{{10}^{-5}}\,to\,{{10}^{0}}S{{m}^{-1}}\]
(iii) Insulators - have high resistivity
\[\rho \tilde{\ }{{10}^{8}}\Omega {{m}^{{}}}\]
\[\sigma \tilde{\ }{{10}^{-8}}S{{m}^{-1}}\]
i.e. the Semiconductors are the materials whose conductivity is more than insulators but less than conductors.
Types of Semiconductors
Intrinsic semiconductors or pure semiconductors in semiconductors forbidden energy gap Eg is more than metals or conductors and less than insulators. Silicon (Si) and Germanium (Ge) are the examples of pure semi-conductors.
In pure or intrinsic semiconductor,
\[{{n}_{e}}={{n}_{h}}={{n}_{i}}\] Where\[{{n}_{e}}=no\].of electrons: \[{{n}_{h}}=no\]. Of holes and\[{{n}_{i}}=no\]. Of intrinsic carrier concentration. Impurity like pentavalent (As, Sb, P) or trivalent (In, B, Al) are added to increase conductivity.
Depending on doping type we have
(a) n- type semiconductor (b) p- type semiconductor
(a) n - type semiconductor: Si or Ge with pentavalent doping. An atom of valency +5 occupies the position of parent atom in crystal lattice. Four valence electrons form 4 covalent bonds but 5th electron is free and weakly bound to parent atom. The ionisation energy (~ 0.01 V for Ge and 0.05V for Si) is small and even at room temperature the electron jumps to conduction band. The dopant is called donor impurity (positively charged).
(b) p - type semiconductor: Si or Ge with trivalent doping means one less electron in the 4 covalent bonds, so the 4th neighbour has a vacancy or hole that can be occupied by an electron from another site. Thus a hole is available for conduction. The trivalent atom is negatively charged as it acquires an electron and is called acceptor atom or impurity.
Formation of p - n junction: Part of p-type can be converted into n - type by adding pentavalent impurity. There is concentration gradient between p and n sides, holes diffuse from p side to n side (\[(P\to n)\]and electrons move from \[(n\to p)\]creating a layer of positive and negative charges on n and p side respectively called depletion layer. External bias is applied to cause charges to flow.
Symbol of p-n junction diode
p-n junction under forward bias: When p-side is connected to positive terminal and n - side to negative terminal of external voltage, it is said to be forward biased.
The applied voltage V is opposite to build in Potential\[{{V}_{0}}\], hence depletion layer width decreases and barrier height is reduced to\[({{V}_{0}}-V)\]. There is minority carrier injection, hence charges begin to flow. Current is in the order of mA.
(c) p-n junction under reverse bias: When p-side of p-n junction is connected to -ve terminal more...
i.e., \[V=\frac{w}{{{q}_{0}}}\]
\[V=-\int\limits_{\infty }^{r}{\overrightarrow{E}.d\overrightarrow{s}}\] i.e. \[E=-\frac{dv}{dr}\] more... 
Symbol of p-n junction diode
p-n junction under forward bias: When p-side is connected to positive terminal and n - side to negative terminal of external voltage, it is said to be forward biased.
The applied voltage V is opposite to build in Potential\[{{V}_{0}}\], hence depletion layer width decreases and barrier height is reduced to\[({{V}_{0}}-V)\]. There is minority carrier injection, hence charges begin to flow. Current is in the order of mA.
(c) p-n junction under reverse bias: When p-side of p-n junction is connected to -ve terminal more... 
