hello hello hello are you all able to hear me and see me well yes har good morning are you all able to hear me and see me well yes ah okay okay okay okay so I started at 5:30 itself Okay so so without any further delay let's get into the topic you will get the marks okay so let's get started start I will finish by 7 o00 7:00 so by 7:00 100% we will be done okay so let's get started people people first of all uh what are the important topics important topics and what are the marks usually they ask two marks or three marks are main are two marks and three marks and the areas are and the op opto electronic devices your photo photo cell and then solar cell and then you have your led the moon important conductors and semiconductors difference using the energy band okay half wve full wave rectifier depletion region diodes and the P Junction diode are you all ready very good very good very good let's get started classification Metals will have very high conductivity so resistivity conductivity resistivity conductivity relation resistivity is reciprocal of conductivity resistivity is a reciprocal of conductivity okay so Metals will have high conductivity low resistivity semiconductors will have moderate moderate insulators will have high resistivity low conductivity got it these are all very very simple okay now uh what are the different types of semiconductors you have elemental semiconductors like your silicon and your germanium okay and you have compound semiconductors which can be inorganic organic organic polymers you can have elemental semiconductors which are silicon and germanium and you have compound semiconductors which can be inorganic organic and organic polymers for our semiconductor chapters and for our daytoday life Modern Life are you all ready super okay so semiconductor insulator if you take it it has something called Valance band conduction band it is still it is still held on by the nucleus that is called Valance band I am talking about a group of atoms which form the metal which form the semiconductor which form the insulator so a group of ATS valence band all the electrons in the last shell so conduction band Val band conduction it is ready to move the electrons are free from the clutches of the nucleus the electrons are fre free from the clutches of the nucleus so up conduction insulators do not conduct electricity why they don't conduct because cond the Gap energy gap forbidden Gap what is this Gap called as energy gap or forbidden Gap are you all clear okay so for insulate this Gap is more than three electron volt this Gap is more than three electron volt semiconduct less than elron Vol then it can conduct electricity then it can conduct electricity super three electron volt less than electron vol why because Metals surface Chum electrons will be freely available electrons will be ready to move so metals are very good conductors because the Gap is almost negligible sometimes it even overlaps got it everybody clear so let's move forward forbidden energy gap for semic less than three insulators more than three electron volt more than three electron volt okays okay let's go forward now what are intrinsic and extrinsic semiconductors okay so intrinsic pure semiconductors okay intrinsic now pure semiconductors like your silicon and your germanium okay so pure silicon pure germanium at 0 Kelvin will not conduct they'll have nothing in conduction band okay at 0 Kelvin there will be nothing in conduction band so the diagram will be Valance B conduction band at 0 Kelvin and room temperature room temperature what is room temperature 27° C room temperature heat is more sud you are giving heat energy these coent bonds Bond in the coent bond electron electron Escape it will move to the conduction it will become a free electron are you all clear EPO at room temperature so when you provide energy to Intrinsic semiconductors then they will start conducting then they will start conducting okay are you guys happy with that super so electon coent Bond coent Bond sharing of electrons electron escap holes and vcy holes everybody clear here so holes are generally considered to be positive charge you know it is the absence of electron so electr holes will be left out are you all clear so the like that conduction will take place so the ini IAL energy was given by heat thermal energy at 0 Kelvin nothing was happening but at room temperature now I have conduction how because one calent Bond the electron got excited and it went into the conduction band so that electron when it leaves it leaves a hole and that hole will be filled by another electron and the electron or hole will be filled by another elect conduction will take place so correct so that is why for intrinsic number of electrons is equal to number of holes are you all clear but guys this is number of electrons per unit volume per unit volume NH now number of holes per unit volume everybody happy so this is equal to n okay I intrinsic charge concentration intrinsic charge concentration okay so into NH is always ni squ this is called as the law of mass action this is called as law of mass action okay for inic this will be true but so for extrinsic this is very important okay so let's move forward so extr extr you add impurity they're Al also called as doped semiconductors they're also called as doped semiconductors did you all like it super so there are two types one is p type next is n type so this is called as P type and this is called as n Type n type now you need to add pentavalent impurity you need to add pentavalent impurity okay and for p type you need to add trivalent impurity you need to add Tri valent impurity got italent Val Val last sh electrons so antimony and then you have phosphorus and the moon electron Alum Boron okay Al silic I'm doing I'm putting an impurity this impurity should be very less few parts per million of the entire lattice okay few parts per million okay that much impurity only should you should add and what are the conditions the conditions are the impurity size should be similar to that of the Silicon which was present in the latice very important okay the impurity size should be similar to that of silicon which was present in the lattice that is very important okay so P Type n type P type in a tri valent now silicon was four electrons but now you have only three electrons so three electrons will be bonded but one will be left out there will be a hole because silicon which was present before had four electrons in the outermost shell so that is why it had four bonds Ando I have only three electrons so 1 2 three but the four one I don't have electron that is a hole got it that is a hole so that is why holes are more so for p type the number of holes are more than number of electrons that is why it is positive P positive P are you all are you all clear with it so same way over here Y type you have pentavalent that means five electrons so phosphorus has five electrons 1 2 3 4 four are bonded but the fifth one is extra the fifth one is extra so you have electrons more that's why n type because electrons are dominating so for n type number of electrons will be more than number of holes did you all like it super are you all clear can you all please let me know in the chat with sare okay super let's go forward okay cool uh yeah yeah now this is very important so uh here pentavalent impurity is giving one free electron it is giving one free electron so it's called Donar impurity it's called Donar impurity in the holes the holes they will accept electrons one electron can jump here so this is acceptor impurity accept our impurity Don our impurity did you all like it everybody okay with it super so now Donar impurity is for n type accept our impurity is for p type so you need to know what is level accept level okay level it is near conduction band okay and accept level it is near Valance band okay doing now son it is adding impurity to a intrinsic semiconductor okay are you all clear now so p and Junction so p and Junction it is important for everything everything P type semiconductor how do you form it is take P type add pent valent impur when you add pent impurity it will become n type so so I will finish by 7:00 like I promised okay so please listen so positive holes P type this is p type and this is n type okay so positive negative they'll attract so El are you all clear are you all clear you will get something like this you will get negative negative negative negative negative and you'll get positive positive positive positive positive correct so everybody clear so electron they will become neutral they will nullify each other correct so depletion region because of this diffusion because of this diffusion the okay majority got it dep okay everybody clear super in the positive negative there will be a potential difference correct so there'll be a potential difference so it positive negative so in the potential difference PA barrier potential in the potential difference pair barri potential for example best example boys H girls H security security okay barri potential barrier potential are you all clear okay so it will not allow further diffusion of electrons into the P type similarly it will not allow further movement or diffusion of holes into the N type okay everybody clear are you all happy with it simple super so that's about it nowo we will study what is forward bias and and reverse bias okay we'll go to diodes are you all happy electr electrons are minor P type holes dominate electr electr electr major they are the major charge carriers but they are the minor charge carriers everybody okay super super super level okay did you like it so far happy Next Level super level great so a drift current will be opposite so diffusion now holes will move from here to here okay diffusion holes move that side that is diffusion current in the barrier potential in the barrier potential positive negative so electric field will be like this electric field is always from positive to negative so it will be like this so holes will be drifting this side because of barrier potential which is created which is as a result of diffusion diffusion barri po the poal holes will be drifting to the left electric field is like this are you all clear okay so let's move forward so forward see forward so forward the depletion region will become so forward forward it will reduce the barrier potential okay forward bi you have P type you have n type correct everybody okay with that barrier potential upo barrier potential AO this will be negative and this will be positive correct barrier potential upo what will happen let me draw a bigger one okay now so barrier potential the P type will be negative and the N type will be positive if you connect the P type to positive terminal and N type to negative terminal of an external battery of an external voltage positive to positive negative to negative that is called forward biasing I will solve questions if you state till 7:00 I will solve questions if you stay till 7:00 positive of the external voltage connected to positive higher potential connected to positive lower potential connected to negative up it is forward bias okay up it is forward bias so forward bias it will oppose the barrier potential so it will reduce the depletion region forward bias will reduce the depletion region and encourage the forward current yeah holes will move that side because positive so positive means electric field will be like this because of this voltage electric field will be like this so holes will move to the right electrons will move to the left everybody clear are you all happy so holes will move to the right electrons will move to the left therefore it is going to be it is going to be having current flow so forward current flow when your V is greater than VB correct if my external voltage is more than this then there will be current flow correcta did you all like it super ran you are right okay everybody clear so Wass I so until until you reach the barrier potential there will be no current but after that it'll increase so this is called as your barrier potential after that it'll increase this is how this is how forward bias will look like this is how forward bias will look like it will increase to very high value it'll increase to very high value where it Peaks is called as threshold threshold potential okay threshold potential for germanium it's 02 and for silicon it's 7 okay for germanium it's 02 for silicon it's 7 where the threshold the limit is reached okay so this is forward bias everybody clear shall we move forward okay so diode Junction easy in the Triangle positive in the code negative triang so if I connect plus over here and minus over here what it what it is forward bias it is called as forward bias the diode is said to be forward biased why because positive to positive negative to negative so forward bias super did you all like it if I put negative here and positive here what bias reverse reverse bias okay reverse bias so I'll give you some more examples let's say you have seven year and four year what bias is this what bias is this reverse or forward this is forward bias why higher potential lower potential like that also you can see like that also you can see got it are you all clear everybody happy with it okay very good very good very good so jagadish I'll come to that so people ideal forward bias diode will have zero resistance what ideal forward bias will have zero resistance ideal reverse bias will have infinite resistance are you here ideal forward bias diode will have zero resistance ideal reverse bias diode will have what infinite resistance clear super so forward bya electrons are flowing easily and holes will flow like that electrons will flow like this holes will flow like that so that is why for forward bias you will have good current you will have current to the order of mli aere you will have current to the order ofr so forward bias current will flow forward from P to n what is the value milliamp okay what happens in forward bias the depletion Zone becomes small the depletion Zone decreases these are all the results of forward bias are you clear shall I move forward very good let's go uh now reverse bias reverse bias reverse bias what happens for for positive P I am connecting negative terminal you see p I'm connecting negative and N I'm connecting positive are you able to see that P negative n positive so that is called reverse bias so reverse reverse resistance will be very high okay reverse bias on the resistance will be very high so current will be almost zero only current will be almost zero only okay and depletion region will become large super level sound correct correct correct okay okay I will do it please listen carefully oh I should remove this one second I wanted to add a slide yeah so I'll EXP exp by drawing that's better okay so reverse you have your uh PN Junction okay so this is your P this is your n and this is your depletion region so when I connect negative terminal and positive terminal like this it's called reverse bias why because this will be also negative and this will be positive so barrier potential external potential they'll be in the same direction barrier potential reverse bias potential they'll be in the same direction so that is why depletion region will become bigger depletion regon will become bigger yo when you have reverse bias current will be current will be zero or very small why resistance is very high reverse resistance reverse resistance okay are you all clear reverse voltage Val it will Peak that is called as breakdown voltage that is called as xener breakdown or Avalanche breakdown it is called as xenor breakdown or Avalanche breakdown see first Reverse by Sinda the field will be like this the field will be like this are you all clear so field what will happen nothing will happen right nothing will happen current will not take place current will not flow so holes will be here and electrons will be here and then here you'll have what diffusion so now there will be minority charge carriers correct minority are electrons electron electrons so because of very high potential you will have higher electric field so these minority charges will also start moving so when they start moving slow current slowly current will come slowly little by little by little but but what will happen at one point they will all start moving together like a group of birds flying together have you guys seen thats BS so these when they move they will collide with Co calent bonds they will break the coent bonds everything will go to the right side the electrons so that is called as Avalanche breakdown because avalan soalan effect so suddenly there will be a very high increase in current that is why you see this graph this is called as xener breakdown or you can call it as breakdown voltage or you can call it as Avalanche breakdown everything is the same okay are you all clear shall we all move forward everybody so forward Bas reverse BAS difference in followed by us positive of external voltage will be connected to P type negative of external voltage will be connected to n type reverse Bas up opposite first difference R the difference forward bias depletion region will reduce reverse bias depletion region will become bigger okay everybody clear third for bias resistance very less reverse bias resistance very high forward bias current will increase okay but reverse bias current will be almost zero but after a certain potential then it'll increase exponentially got it so these are the differences are you all clear let's go let's go let's go time much so now rectifier okay rectifier is very very easy I'll tell you simple see you have a alternating current AC AC DC AC is alternating current DC is direct current I want to change AC to DC Al very simple now AC current I will supply it to this circuit main circuit inductor to transfer the AC setup okay just to transfer the AC over there so let us see the first cycle it positive so it's positive the first half everybody clear are you all happy with it everybody please let me know so when it is positive when it is supplied here you'll have plus here and you'll have minus here okay now the AC current if I supplying over here let's say this is positive and this is minus now diode diode will be forward bias yes forward bias positive P triangle is p the code is n so plus with positive is forward bias so followed by supper diode is conducting diode will have current super Sol when it is forward bias diode will conduct so output will be what output will be like this super okay sir sir now next half cycle next half cycle will be reverse Direction it will be reverse Direction reverse Direction this will become this will become negative this will become positive it'll become reverse so now reverse means negative is connected to p and positive is connected to n that means it is reverse bias if it is reverse bias there will be no current there will be no current no output level did you all like it some EAS now again positive direction positive direction means this will be positive this will be negative now again forward bias forward bias okay yeah positive with triangle so again conduct half wave of the full wave of the full wave that's why it's called half wave rectifier okay let's go to full full wave rectifier so full wave you will keep two d you will keep two so you are giving AC Supply so first half cycle first half cycle I have plus here minus here super I have plus here minus hereo for the first half cycle in the okay so this diode will be forward this diode will be reverse let's call this D1 and D2 do you all agree D1 will be forward byas D2 will be reversed by S so which will conduct current D1 so D1 will transmit and I will get output half wve everybody clear reverse the direction now the next half reverse the direction if I reverse it this will become minus this will become plus now D1 is reverse bias so D1 will not conduct but D2 is forward bias so D2 will conduct so I have again output that will be from D2 so you see same direction I'm getting full wave output that's called as full wave rectifier okay it's very easy okay I hope you all liked it that's the concept okay so okay let's go forward uh now opto electronic devices okay when the depletion region will break mugan Rohit uh when you have breakdown voltage at breakdown voltage or xener breakdown the diode will break it will be damaged permanently okay so now last top question okay okay so it's good last last three topics everybody photo diode photo it is a device used to understand how bright how bright the light is how intense the light is okay everybody is clear with it everybody what is knee voltage a knee voltage forward bias the moment your current starts flowing that's called knee voltage so a a forward so forward byas up to your barrier potential there will be no current after barrier potential your current will increase so this is called as knee potential this is called as knee potential or knee voltage because of the shape okay everybody clear did you all like it so that is the definition of knee potential threshold potential also you should know threshold potential is the breakdown on the forward side reverse Biers breakdown you guys know on the forward bias also you can have breakdown that is called as threshold voltage both threshold voltage in the for forward side breakdown voltage in the reverse side will be given in the diode the manufacturer will mention very good now photo diode photo diode is a device used to find out the brightness intensity of light Okay so photo diode will be a p Junction diode in Reverse bias photo diode and Xena diode are reverse bias make a note of it photo diode and Xena diode are both reverse bias okay why reverse bias I will explain please wait first let me take time to go through this okay so first for photo diode we want a bigger depletion region mother Point doubt not the first point is I want a bigger depletion region why sir because whatever incident photons are coming what will they do what will they do they break those bonds and they'll form electrons and holes did you you get it the incident photons in atoms bonds they will break and they'll form electrons and holes correct they will separate electrons and holes in the depletion region so in the depletion region light will fall light will fall in the depletion region it will separate electrons and holes by removing bonds by breaking them okay are you all clear so in other words what you can say is it will exite electrons to go into the conduction band okay so electrons will come out so electrons and holes will be created are you all clear before they recombine before they recombine what will happen the holes will be separated to the left and the electrons will be separated to the right this is very important holes will be separated to the left electrons will be separated to the right okay so there will be a current flow holes will flow like this electron right Lona conventional current is left so current will flow like this in the circuit so depending on how many depending on how many photons are falling that many that much current you will get so more intensity more current that is what you're seeing here you see reverse bias they have drawn four graph which has more current the last one so what does that mean the last one is intense light highly intense light did you all like it are you all clear so intensity current that is what you learn from photo diode why why because in phons there will be more electrons which come out so that will supply energy to the electrons to come into the conduction band and that will create holes so Photon you will get electron and holes holes will come to the left electron will go to the right yeah reverse bias reverse bias now electric field will be like this reverse bias means like this right negative to P type positive to n type so electric field will be to the left side if electric field is to the left side then holdes will come to the left electrons will go to the right so whole current will be like this electron right paa conventional current is to the left so the current will flow like this in the circuit so it is flowing in the reverse Direction that's why it's negative that's why it's negative got it so reverse bias you'll get Negative current but as your intensity increases that is Nara Nara light fall PA then there'll be more electrons clear so then there'll be more current and as your current increases brightness intensity increases so we dedu light did you all like it level so shall we move forward very good very good yes yes yes yes so these are the reasons why we need to use reverse bias reason reverse bias current will be zero the diffusion current will be zero so it won't affect these values and now forward bias there will be diffusion current so it will affect whatever reading that we get okay so that is also one more reason why we don't use forward bias we use reverse bias okay did you all like it very good very good very good so yeah let's move forward guys next one Led Led we use forward bias for Led we use forward bias see Moon device Moon bias photo diode reverse bias Led Led is forward bias solar cell is no bias solar cell is no bias okay did you all like it everybody clear super so now LEDs forward bias that means your positive your positive is connected to P type your negative is connected to n type are you all clear everybody super simple H I'll finish it off in five minutes guys that's it five minutes now what will happen so plus minus now electric field will be like this because forward bias electric field will be like this so your holes will move to the right electrons will move to the left correct holes will move to the right and electrons will move to the left super everybody clear so now when they move like that they will collide and they will recombine okay they will collide and they will recombine so what will happen at that time at that time what will happen at that time the electron from the conduction band will come to the valance band electron from the conduction band will come into the valance band so when it is coming down it will release some energy correct it will release some energy that energy will be equal to the Forbidden energy gap that energy which I release will be equal to the Forbidden energy gap so that is what you see as light that is what you see as light are you all happy where level of a did you all like it so H new is equal to EG so new is the frequency H is planks constant EG is what energy gap The Forbidden energy gap okay are you all happy with that super did you all like it so if this if this is in such a way that the frequency is frequency of visible light then you can see it so what is frequency it is energy gap by H if this frequency lies in visible region then you you will be able to see it okay are you all clear LED next last one is solar cell so solar cell is no bias forever solar cell is no forward no reverse okay what is the concept light will fall light will fall on the depletion region light light will fall on the depletion region then what will happen can you guys tell me can you guys tell me what will happen everybody please super super super super so what is the purpose of solar cell solar cell is to convert light energy into electrical energy Enric okay so when that happens what will happen initially you'll have all the negative here and all the positive here are you all clear everybody okay with it so what will happen when light falls like Photo diode and now it will create holes and electrons it will create holes and electrons okay so the holes positive will be attracted to the left negative and the electron will be attracted to the right are you all clear so there will be a current flow there will be a current flow positive to the left negative to the right so current flow will be like this so this is the concept of solar cell concept elect it will exite valence B electon it will exite and then you will get one electron conduction one hole will also be created so the hole will be attracted to the left why because this is negative this is negative barrier potential barrier potential this will be negative no so whole attracted to the negative electron attracted to the positive so there will be current flowing like this okay that is the concept over so this is the graph in the graph just memorize it this is the graph for solar cell okay right now no time to understand just memorize it we not open circuit and I short circuit so the graph is like this all okay so let's go to questions come on guys let's do it fast fast in the graph anger in in the graph finger board exam K this is board exam K come on everybody try to solve it fast everybody please try to solve it fast come on guys LED there's no graph man okay please please answer fast phoe photo diode solar cell answer photo diode solar cell two marks you got two marks over got it let's go to the next one uh show on a plot variation of resistivity of conductor and semiconductor as a function of temperature semiconductor resistivity decreases with temperature for conductors resistivity increases with temperature correct everybody cool with that for conductors resistivity increases with temperature for semiconductors resistivity decreases with temperature why why because of this formula resistivity is equal to M by n e s to what is to to is relaxation time so mainly because of this so for Metals when you increase the temperature relaxation time will decrease for Metals when you increase the temperature the collisions will be very fast so relaxation time will decrease so if relaxation time decreases then resistivity will increase semiconductors resistivity because for semiconductors relaxation time will not change much will not change much okay are you all happy let's go uh that's the reason I will share the PDF class I will share it okay so now next one very good question this is a very good question what is the reason for photo diode to operate in Reverse bias first reason I want a big depletion region I want a big depletion region so that will happen only in reverse bias correct first point R the point what is the second point the current in Reverse bias is zero got it is almost zero or negligible and hence we can get a clear idea of of intensity versus photocurrent we can easily deduct intensity versus photoc current because in Reverse bias the current is negligible an forward basla current is not negligible current will be milliamp okay did you all like it are you all happy now uh a PN photo diode is fabricated from semiconductor with a band Gap so EG is how much 2.5 EV so what did I say uh the frequency H new is equal to energy correct so it is HC by Lambda so what is Lambda 2.5 electron volt I will write as 1.6 into 10^ - 19 by uh okay this is 1 by Lambda so that will be by 3 into 10^ 8 into 6.6 into 10 - 34 so that is your answer I hope you all liked it okay so solve this get the value of wavel you are done okay PD okay are you all okay shall we move forward super yeah super yeah super yeah so this is how you solve it I hope you all liked it okay hey this is a direct formula if you want you remember this this is a direct formula shortcut HC by EA it's equal to 1242 EV by 2.5 EV into anstrom it's a shortcut formula okay so let's move forward now come on guys quickly forward bias because only forward bias will conduct only forward bias will conduct electricity very good B1 is Right super yeah where a level where a level so plus minus so minus minus so minus is connected to P this is p this is n this is p this is n so plus is connected to P here minus is connected to P so this is reverse bias this is forward bias so Conn only this will conduct so B1 will glow that's it it is not difficult okay super everybody cool did you all like it all of you are happy super super super okay next one draw a diagram of illuminated PN Junction solar cell so diagram you have to draw I will show you I don't know whether I have it okay I can show you guys so you take a PN Junction without any bias it should have a depletion region so this is p this is n and this is a depletion region so depletion region will have what barrier potential so this is called as your barrier potential okay so this is your uh solar cell your light will fall here once light will fall here it will exite electron so you'll have electron and you have holes the holes will move to the left and the electron will move to the right so all the holes will move to to the left all the electrons will move to the right so this will become negative this will become positive so there will be a EMF there will be a EMF this is positive and this is negative so you can get an EMF out of this okay so that is the working of a solar cell I hope all of you liked it everybody clear where level is simple diagram P type n type okay depletion region light dep will exite electrons to conduction band so you'll have electrons and holes the holes will be attracted to the left electrons will be attracted to the right so left will become positive right will become negative so positive negative means I can create potential difference I can create an EMF that's it over are you all clear okay okay okay okay let's go let's go let's go quickly come on guys uh in the following diagram yes is a semiconductor what will happen if you increase the temperature they saying I want to keep the current constant current Conant okay so what should you do to the value of R when s is heated when semiconductors are heated resistivity will come down correct when semiconductors are heated resistivity will come down so resistance over here will come down so if I have to maintain same current then this has to increase this resistance will come down so this resistance has to increase so the answer is increase R increase R because when you increase temperature for semiconductors resistivity will come down resistivity come down means resistance will come down so the resistance offered by this will reduce so if the resistance offered by this is reduced I want to keep the current constant so obviously I need to increase r okay did you all like it super oh super next photo diode photo diode is very important you get so many questions so photo diode is a device used to detect the brightness of Light how intense it is okay so light will fall depending on intensity you will get photocurrent okay so the graph is like this the graph will be like this this very important okay so you'll have graph like this so intensity higher I4 is highest i1 is lowest I4 is the highest got it so intensity current inity super did you all like it are you all clear VI graph V on x-axis I on Y axis okay voltage on the x-axis I current on the y- axis okay very good very good uh that's about it so photo diode is negative uh reverse bias photo diode and Xeno diode are reverse bias LED forward bias solar cell no no bias no bias okay next one uh where is the resistance negative where is the resistance negative here please tell me everybody please go for it come on guys please tell me where is the resistance negative resistance negative over here BC very good ar ar very good okay Abdul Rahim ausan Chad very good BC is correct okay BC region the resistance is negative why because slope slope is negative whenever you have VI or IV graph if your slope hope is negative then your resistance is negative okay that's it okay next one uh VI characteristic of PN Junction diode Uh current is independent of okay I will share this okay depletion region I told you how it is form so we'll go to better questions oh okay so distinguishing features between conductors semiconductors and insulators conductors energy band will overlap for conduction and Valance semiconductors energy gap is less than 3 electron volt insulators energy gap is more than 3 electron volt okay so those are the differences you should know are you all clear very good now let's move forward case based come on guys quickly quickly quickly everybody tell me which one is right everybody please let me know quickly this question last 5 minutes last 5 minutes so you see here this is positive so Earth means zero this is two so negative is higher poti so this is reverse bias now here - 10 0 and this is positive this is negative so - 10 positive again reverse bias here 2 + two is positive and + 7 is negative so again reverse bias so this is the answer why because + 5 is NE and + 7 is positive so 7 positive 5 negative triangle positive Cod negative okay done so let's go next K diode diode V diode VI characteristic will be like this followed byas will be like this reverse bias will be like this okay so this is reverse bias followed byas so is it linear it is not linear therefore non omic because omic means V is proportional to I but here this is V this is I are they proportional no it is behaving random exp exponential okay are you all clear very good next one uh ratio of forward bias to reverse bias see forward bias low resistance reverse bias will have high resistance so how do you do it resistance is what resistance is Delta V by Delta I so V is changing by 10 I is changing by 1 microampere for reverse bias for forward bias it will be Delta V Delta V is what 0.1 Delta V is 0.1 Delta I is 20 - 10 so that is forward bias this is reverse bias so take the ratio you'll get the answer so I think the answer will be 10^ minus 6 because forward by reverse forward is small reverse is Big forward is small reverse is Big so obviously it should be less than one so none of the options are less than one so obviously option D Common Sense okay did you all like it but I told you the correct approach also so this is what this is 10 the power + 5 this is what 10 the power -2 something like that okay everybody cool did you all like it par level are you all happy now that's it you can finish it off okay so let's move forward what is the direction of conventional current conventional current direction on it is like this option C is correct why option C is correct because when you apply positive minus then the electric field will be like this so an electric field is like this the holes will move to the right the holes will move to the right the electrons will move to the left so C is correct the holes will move to the right the electrons will move to the left why because positive negative so field electric field electric field will be from plus to minus got it everybody clear great so that's about it uh can you guys try to solve this ideal diode ideal what diode forward bias because this is + three this is + one so you have higher potential to positive and lower potential to negative so it is forward bias forward bias the resistance is zero ideal forward byas diode resistance is zero so what is the current potential difference is what potential difference is two so current will be equal to potential difference by resistance so 2 by 200 2x 200 is what option C did you all like it it LEL did you all like it everybody clear super now energy band come on guys finish it off insulator energy band is more than three logic gates Xena diod okay that's it so next one uh next one is What conduction band and Valance band separation for Semiconductor is one it should be one because for Semiconductor it is going to be less than three electron volt for Semiconductor for insulator it is more than three electron Vol so in this option b is correct option b is correct it should be less than three so less than one zero zal zeroa conductor okay and uh the forent Gap is smallest in conductors obviously because conductors the they overlap conduction band and bance band they will almost overlap so the Gap is smallest in conductors okay the Gap is smallest in conductors okay so now what is the answer the answer is option A why option A because see carbon only two shells silicon three shells germanium shells are more so car it is very close to the nucleus silicon German EAS that is why free electrons in germanium and your silic are high but very small in carbon okay did you all like it okay and solids having highest energy level partially filled with electrons are solids having highest energy level partially filled with electrons are conductors it's a very good question answer is conductors over so did you all like it I hope you all enjoyed the session so do well in your exam guys all the very best okay I tried to do my best but yeah it was very short time semiconductors we didn't have time but anyway all the very best and today at 2:00 we'll discuss it okay take care take care okay guys take care care all the best okay bye-bye guys take care see you see you see you all the very best and performance fire okay thank you so much guys take care see you in the next one bye-bye