Current Electricity/Grade-12/JEE/NEET/Physics

Added: 2026-05-25

[00:03:39]Hello students, welcome to the student the brand.

[00:03:49]Hello students, welcome to the student the brand. This is today topic is current electricity.

[00:03:57]Current electricity. Okay. So let's discuss about it. Let's discuss about it. So the rate of flow of charge is called the rate of law of charge is called electric current.

[00:04:11]Rate of law of charge is called electric current. Right?

[00:04:29]So the rate of flow of charge is called electric current. I = Q byt or simply we can say the rate of flow of net charge through a unit cross-sectional area per second. Okay. So net charge through a unit cross-sectional area per second is called electric current. That that is average current. That that is average current. Coming to instantaneous current I = DQ by DT. Okay. I = DQ by DT. So today topic is current electricity.

[00:05:17]Current Current electricity.

[00:05:29]Okay. Current electricity.

[00:05:32]So SI unit of current is ampere. SI unit of charge is kum. SI rate of time is second. Okay. What is SI rate of current? Ampere. SI rate of charge kum.

[00:05:46]SI rate of time second. So I = Q by T.

[00:05:52]So here average current here average current I = DQ by DT. So instantaneous current instantaneous current understood or not? So the rate of flow of net charge the rate of flow of net charge through a unit cross-sectional area through a unit cross-sectional area per second per second is called electric current understood or not so I = Q byt I = Q byt so of current is amp Sin unit of current is ampere.

[00:06:39]Sinate of current is ampere. And asset of charges column.

[00:06:46]SI unit of charges column. Sinate of time is second.

[00:06:51]Sinate of time is second. So 1 ampere is defined as 1 ampere is defined as. So here 1 ampere equal to 1 kum per 1 second. 1 ampere equal to 1 kum per 1 second. Understood or not? So 1 ampere is defined as 1 kum of charge flowing through unit cross-sectional area per second. 1 ampere is defined as 1 kum of charge flowing through unit cross-sectional area per second is called electric current is called electric current. Yes or no? Yes. So here if the electrons are moving in the conductor so here only one electron only two electrons only three electrons. So here you can see only one electrons flows will you say current is flowing only two electrons flows will you say current is flowing only three electrons flows will you say current is flowing no we can't say like that right number of charges are moving in the conductor number of charges are moving in the conductor then only we can say current is flowing in the conductor right so that's why charge is quantized charge is quantized Q = plus plus or minus N. Q = plus or minus N. Understood or not? Q = plus or minus N. So N is the number of charges and one electron 1.6 into 10^ -19 kum and one electron and one electron 6 and one electron 1.6 6 into 10^ -19 column in 1 column in 1 column 1 by 1.6 into 10^ -19 then you will get so 1 by 1.6 into 10^9 then I'm taking here 0.625 into 10^ 8 19 okay in one column so one column if you're taking 6.2 25 into 10^ 18 electrons.

[00:09:16]Okay. So this is very very important.

[00:09:18]These two points are very very important. Observe carefully. So I = Q byt. Sate of current is ampere. Sate of charge is kum. Sinate of time is second.

[00:09:31]I = dq by dt. I = dq by dt instantaneous current. I = Q byt is the average current. 1 amp is defined as 1 colum charge flowing through unit cross-sectional area per second. So only one electrons flows will you say current is flowing only two electrons flows will you say current is flowing. So we can't say like this. So number of charges are moving in the conductor then only we can say current is flowing s. So that's why so on and one Q = plus or minus N that is quantization of charge quantization of charge on one electron 1.6 into 10^ -19 column in 1 colum 1 by 1.6 into 10 -9 then 1 colum 6.25 into 10^ 18 electrons are present. Understood or so this is about this is about electric current quantization of charge and uh so next one is number of charges are there and one electron and number of electrons present in one colum. So everything we discussed now we'll discuss about electrical appliances.

[00:10:53]So each and every point we'll discuss each and every point we discussed. Okay.

[00:11:00]So one by one by one we will discuss all points. Let's start discuss about it. So now electrical appliances electrical appliances we'll discuss those are. So here you can see positive terminal positive terminal negative terminal cell. This one is a cell coming to the battery.

[00:11:27]Battery positive terminal negative term.

[00:11:29]This is a battery.

[00:11:32]Battery.

[00:11:35]And coming to the third one. So switch.

[00:11:40]So open switch.

[00:11:44]Open switch.

[00:11:47]And coming to the fourth one. Closed switch.

[00:11:59]Open switch and closer switch.

[00:12:03]open switch and closer switch. And coming to the fifth one, resistor resistor.

[00:12:16]And coming to 61 rear start reart.

[00:12:34]Coming to the seventh one ammeter.

[00:12:42]Ameter.

[00:12:44]Eighth one voltmeter.

[00:12:51]Ninth one wire joining.

[00:12:56]So here you can see this is for 12th grade current electricity.

[00:13:04]Okay. cell, battery, open switch, closer switch, resistor, riost, ammeter, voltmeter, wire joining and uh 10th one is wire crossing, wire crossing and 11th one is bulb.

[00:13:25]Okay. So electrical bulb understood or not? So this electrical bulb is it symbol for electrical bulb is it clear or not? So cell cell battery open switch closed switch resistor. Here we are to discuss about resistor.

[00:13:46]Resistor is a device which is used to oppose electric current. Resistor is a device which is used to oppose the electric current in an electric circuit.

[00:13:56]Okay. Resistance is the phenomena of opposing the electric current.

[00:14:01]Resistance is the phenomena of opposing electric current. So here you can see resistor.

[00:14:12]So one by one we will discuss So now now we'll discuss about uh resistor resistor So resistor is a device. Resistor is a device which is used to oppose electric current. Okay. Here three points you have to remember. One is resistor.

[00:15:11]Second one is resistance.

[00:15:15]Resistance.

[00:15:18]And the third one is ohm.

[00:15:21]And the fourth one is symbol. Okay. So first one you can see resistor is a device which is used to oppose electric current. Resistor is a device which is used to oppose the electric current in an electric circuit. Resistance is the phenomena of opposing the electric current. Resistance is the phenomena of opposing the electric current. And coming to the S unit of resistance is oh sit of resistance is oh and a symbol for resistance symbol for resistance. So this is about resistor. Coming to Rio start coming to RI start.

[00:16:05]So Rio start I'm discussing. So this are your start.

[00:16:11]Rio start either you can draw like this or like this also we can take it.

[00:16:20]Okay. Rio start.

[00:16:25]So what is the use of RIO start? Rioart is a device which is used to regulate the current. Rio start is a device which is used to regulate the current without changing the voltage source without changing the voltage source. So that is about riost and coming to the ammeter.

[00:16:45]Ameter is a device. Okay. So I'm taking ameter.

[00:16:53]So once again amter and voltmeter will be connected together. ammeter and sorry amter and voltmeter I will explain together not connected together so this ammeter a meter and coming to the voltmeter so amter is a device amter is a device which is used to measure electric current okay is a device which is used to measure electric current in an electric circuit Okay. Amempter will be connected in series combination. Coming to the voltmeter. Voltmeter is a device which is used to measure potential difference. Okay. The difference in electrical pressure. The difference in electrical pressure is called potential difference. So that also we can say work done to bring unit positive charge from one point to another point within the conductor. Okay. So those points also we'll discuss. So here potential difference. So what is the potential difference? Potential difference.

[00:18:00]Potential difference.

[00:18:05]Okay. Work done to bring. So I'm taking here is the conductor point A to point B. So positive charge is there. We are doing work. So positive charge is there.

[00:18:16]We are doing some work. Okay. Work done to bring unit positive charge from one point to another point within the conductor. within the conductor is called potential difference. V = W by Q.

[00:18:29]So S of potential is volt. SI of work is J. Sate of charge is kum. So one volt is defined as one volt is defined as one J of work is done to bring one kum of charge from one point to another point.

[00:18:44]One point another point that is potential difference within the conductor. Within the conductor. Coming to the electrical potential.

[00:18:52]Electrical potential.

[00:18:57]Electrical potential.

[00:19:02]Electrical potential is nothing but so positive charge is there infinity. So we are doing some work. So this the required field. So we are doing some work to bring unit positive charge. We are doing some work to bring unit positive charge from minifinity to the required field. from infinity to the required field is called electrical potential. Understood or not? Potential difference is nothing but work done to bring unit positive charge from one point to another point within the conductor is called potential difference. Work done to bring unit positive charge from infinity to the required field is called electrical potential. Electrical potential.

[00:19:42]Understood or not? So, voltmeter is a device which is used to measure the potential difference. Volto is a device which is used to measure the potential difference. Is it clear or not?

[00:19:55]Is it clear or not? Yes or no?

[00:20:01]So here two more points I'll discuss.

[00:20:04]Two more point I'll discuss. So voltmeter will be connected in series combination. Sorry. Voltter will be connected in par combination. Ameter will be connected in series combination.

[00:20:16]Okay. ammeter will be connected in series combination. So because so when you connect in parall combination. So if ammeter is connected in parall combination amter has some fixed reading. Okay. So in voltter different appliances operate at different voltage.

[00:20:35]Okay. So more current is required. Then what happens? So different potential difference different uh current. Okay.

[00:20:44]So uh different appliances operate at different currents understood or not. So when uh extra current goes than its required limit or then it is fixed limit then it measures limit. Okay then what happens amter gets slightly heated slightly gets heated. Is it clear or not? So that's why amter is not connected in parall combination. So whereas voltmeter so voltmeter will be connected in parall combination voltmeter will not be connected in series combination. Why voltmeter measures potential difference.

[00:21:20]Voltter measures potential difference.

[00:21:23]If voltmeter is connected in series combination in series combination throughout the path current is same.

[00:21:29]Right? In series combination throughout the path current is same. So how it will measure same current is flowing some difference must be there okay some difference must be there then only voltmeter measures the potential difference okay so that's enough that is the reason we are not connecting ammeter in par combination voltmeter in series combination okay so next we will discuss about next we will discuss about electric circuit electric circuit here convention current and electric current. We'll discuss electric circuit.

[00:22:08]So here is the bulb. Here is the bulb.

[00:22:11]Bulb and amter.

[00:22:15]Okay. So here is the battery switch.

[00:22:22]So current is passing like this.

[00:22:27]Pass to terminal bulb is glowing.

[00:22:31]Okay. So point number one here we are to discuss about two points one is conventional current and electric current. Conventional current.

[00:22:43]Conventional current and electric current.

[00:22:47]Second one is electric current.

[00:22:51]Electric current.

[00:22:54]So what about conventional current?

[00:22:56]Conventional current is nothing but so flow positive charges. The direction of flow of positive charges will be taken as direction of conventional current that is nothing but positive charges are moving from positive charges are moving from positive terminal to negative terminal. So positive charges are moving from high potential to low potential that is nothing but positive terminal to negative terminal. Whereas electrons are moving from negative terminal to positive terminal. Electrons are moving from negative terminal to positive terminal that is low potential to high potential that is negative terminal to positive terminal. Understood or not? So this is about conventional current and electric current. Conventional current and electric current. Is it clear or not? Once again observe carefully. So conventional current is nothing but the flow of positive charges. Okay. So the flow of positive charges direction is taken as the uh direction of conventional current and the flow of electrons flow of electrons is taken as electric current. The flow of electrons direction is taken as convent electric current direction. Electric current direction understood or not? So I hope it is very clear. So next one we will discuss about Next one we will discuss about.

[00:24:32]So DC and AC first one is DC and AC.

[00:24:41]Okay. So DC is nothing but direct current. AC is nothing but alternative current. Okay. So DC in DC both the magnitude and direction of current does not change with respect to time. Both magnitude and direction does not change with respect to time that is called DC.

[00:25:07]So coming to AC both magnitude and direction changes with respect to time.

[00:25:13]both magnitude and direction changes with respect to time. Okay. So example for uh DC one is cell cell battery cell battery and DC dynamo DC dynamo. Coming to the AC AC dynamo AC dynamo understood or not? Yes. So now you can see here alternative current.

[00:25:46]Alternative current. Okay. So now you can see if the charge is moving a circular path. So charge is moving in a circular path with frequency F. If charge is moving in a circular path with frequency F. I = QF. I = QF. Understood or not? So DC is nothing but direct current. So in direct current both magnitude and direction does not change with respect to time example cell battery and DC dynamo. Coming to the alternative current in alternative current okay like AC so both the magnitude and direction changes with respect to time with respect to time is it clear or not so that's why uh example for AC is AC dynamo if the charge is moving a circular path if the charges move a circular path so current will be taken I equal to QF I= to QF Is it clear or not?

[00:26:53]Next. So coming to the next one.

[00:26:57]Coming to the next one that is.

[00:27:09]So I'll discuss about drift velocity and relaxation time.

[00:27:16]Drift velocity and relaxation time. So let's discuss about it. Drift to velocity.

[00:27:24]Drift to velocity.

[00:27:32]Drift to velocity and relaxation time.

[00:27:43]So here you can see this the conductor.

[00:27:47]So this is the conductor. Understood or not? This is a conductor. So current is passing in this direction. So electrical field will be there in this direction.

[00:27:58]So electrons are moving opposite to the electrical field. Electrons are moving opposite to the electrical field. That is a drift velocity. Electrons are moving opposite to the electrical field.

[00:28:11]So that is a drift velocity. Is it clear or not? So now when electrons are moving in an electrical field when electrons are moving in an electrical field it experience some force. Is it clear or not? When electrons are moving in an electrical field it experience some force. So that is FB = Q R E. Understood or not? So when electrons are experiencing experiencing some force then automatically produce acceleration.

[00:28:48]When electrons are moving in an electrical field it experience some force. So that force will produce acceleration. Yes. So that is F= M A F = M A. So M A = Q R E. So a = q by m that is e by m understood or not? So I hope it is very clear. I hope it is very clear now. So next we will see here drift velocity and relaxation time. We have to discuss drift to velocity and relaxation time. So point number one drift to velocity drift to velocity and relaxation time.

[00:29:41]Drift to velocity and relaxation time.

[00:29:45]Is it clear or not?

[00:29:48]Is it clear? Drift to velocity and relaxation time. Relaxation.

[00:29:56]Relaxation time.

[00:29:59]So coming to driftive velocity normally electrons are moving in an electric circuit like uh in the conductor electrons are moving in the conductor.

[00:30:16]Okay. So normally if if place is there if space is there so people can move happily. So uh in that way so the way which they are going that is very less space okay so very less space so we have to go in a particular direction that to in a less space in a less space right suppose if you are taking like this okay this is the way so I'm moving in this way so in this way very less space is there very less space okay more number of more number of Students are moving more number of people are moving in one direction then what happens? So there must be classes here. If electrons are moving in a closed enclosure within a less space then what happen for initially electron is moving some velocity like 2 m like suppose you are taking some velocity you can take. So this electron is moving some velocity. This electron is moving some velocity and this electron is moving like that. So each electron having different velocity I know. So different velocity each electron has different velocity. What happens this anyway they are moving in a closed enclosure in a closed path in one direction then one electron will eat another electron. One electron will eat another electron that electron is going to eat another electron like that. Keep on bombardment takes place. Keep on collisions will takes place. SO keep on collisions will takes place. This electron is going to hit this electron.

[00:32:01]This electron is going to 10 electron.

[00:32:04]Like see before the electron has some velocity. Okay. So electron has some velocity. After collision the velocity will vary. The velocity will change. Yes or no? Yes. So the average velocity of an electron moving in a conductor the average velocity we have to take suppose in a class. So one student got 25 marks, one student got 30 marks, one student got uh 50 marks, one student got 40 marks out of 40 only one student got uh like at like we can say 45 marks, one student got 37 marks like that. So every people so students are getting different marks. If you take average so average of those uh number then for person how much we'll get that is the average of the particular student okay average total average so in a class so here also we are taking when electron is moving to some velocity after collision so the velocity of an electron changes initially early morning we'll wake up with so much energy right so we'll do all the works all the works so like homework class work listening writing reading preparing writing exams we do so much works at the end we lose energy we lose that speed we lose that velocity okay so we will be tied in the end of the day so at the end of the day we are tired so here also before collisions the velocity of electron will be different.

[00:33:52]After collision the velocity will be different. Yes or no? Before collision velocity will be different. After collision velocity will be different.

[00:34:00]The average velocity of an electron moving in an moving in a conductor.

[00:34:06]Okay. So that is called drift velocity.

[00:34:10]Drift to velocity sir. Okay sir. Drift to velocity we understood. What about relaxation time? So you said relaxation time. Relaxation time is nothing but so normally you can see as I mentioned so electrons are moving in a closed conductor within less space that in one direction. Okay. So collisions will takes place. Average velocity of an electron moving in a conductor is called drift velocity that we know that. Now we have to talk about relaxation time. SN relaxation time. So uh I'm moving in a conductor. So I I hit the one electron, right? So like so electron is going to hit another electron. So after that one more collision after that one more collision like that collisions will takes place. So will this collisions takes place at regular intervals of time? Okay. So early morning electron should wake up. So do the brush, do the broth. Okay.

[00:35:15]Do eat the tiffen and so get ready for the collisions like that electron will think and get ready for the collision.

[00:35:24]So yes, exactly. So like we are going to college like exactly 8:30 p.m. 8:30 a.m.

[00:35:32]8:30 a.m. I have to be in the college like that electron will think. Yes. No.

[00:35:36]Now I so I have to go and hit the electron in present in the conductor. So I should get up and do brush and do bathing do everything. Okay. So and do dress up neatly and take the bag and go and hit the other electron present in the conductor. Will it do that? No.

[00:35:55]Right? So it won't happens on regular intervals. Right? It won't happens on regular intervals. So it will happens on random intervals. Nothing. So how it will be? So get up and go and eat the another electron. That's enough. So in in a conductor one electron is going to eat another electron. That's enough. Randomly it takes place. Collisions will takes place randomly. It won't takes place regularly. Okay. So randomly takes place but between one collision to another collision some gap will be there right.

[00:36:30]So between one collision to another collision. So uh electron is going to another electron after that immediately.

[00:36:37]So going to another electron. So some gap must be there right. So there is a time gap between one collision to another collision. One collision to like uh so our periods are there right? So 45 minutes after that uh again next period after that again after that after lunch time again next like that there is a time gap yes I know there is a time so here also we'll see so between one collision to another collision there is a time gap there is a time gap yes I know so that the average time gap between two successive collisions okay so we should not take so this the first collision after there 75th collision after that 86 collision I have to take the time. No, we should not take like that. So the average time gap between two successive collisions, one collision to another collision. So like that we have to take like that we have to take.

[00:37:30]Understood or not? So that is the relaxation time. Relaxation time. Is it clear or not? So these points are very very important. These points are very very important. So now we'll discuss about one more that is so current and drift to velocity current and drift to velocity current and drift. drift velocity. Okay, let's discuss about it. Current current and drift velocity, current and drift velocity. Okay. So this is a conductor. I'm taking the conductor like this. This is the conductor and area of the cross-section is A.

[00:38:44]And here also area of the cross-section is A and here we are taking this length of the conductor Length of the conductor. So only within this this area of the cross-section area of the cross-section area of the cross-section and here the time interval is there. So time interval delta t time interval delta t. So electrons are moving in the conductor anyway current is moving in this direction. So electrical field will be there and electrons are moving in the conductor like this. So through this cross-sectional area W D I'm taking here W D understood or not? So VD I'm taking now S and O electrons are moving in the conductor. So normally velocity equal to what is the formula? V = L by T. So here here we are taking V D W D = L into deltaT. So length equal to V D into delta T. Is it clear? Length of the conductor. So this length of the conductor is L = W D into delta T. So W D into delta T. Is it clear? So what about volume? So volume what is the volume formula? Volume= to length into area of the cross-section. Volume= to length into area of the cross-section.

[00:40:25]Length is how much? W D into delta T into A. This is the volume volume of this particular conductor. Okay. So from A to A. Understood or not? Now what about electrons? Number of electrons present in the particular volume. Number of electrons present in the particular volume that is number of electrons.

[00:40:51]Number of electrons.

[00:40:54]Number of electrons.

[00:40:57]Okay. That is n is the free electron density. Small n is the free electron density. Is it clear or not? So now n into v d into delta t into a. Okay. So what about quantization of charge? Delta Q = delta Q = So N B D delta T into A into E quantization of charge. So now what about current? What about current?

[00:41:33]I = I = delta Q by delta T. I = delta Q by delta T. NV D delta T A E by delta T. So delta T delta T get cancel. So shall I cancel delta T delta T? Then what is the remaining? N E V D into A. So I = N A V D.

[00:42:04]Okay. So this the relation between current and drift velocity. Relation between current and drift velocity. Is it clear or not? So what about current density? So this formula is very very important. Relation between current and drift velocity.

[00:42:22]Okay. What about current density?

[00:42:25]Current density J = I by A. Current density J = I by A. Okay. So n e a v d by a. So shall I cancel a a? So I'm canceling a. So what is the current density final formula? Current density j = n e v. Is it clear or not? So this is the formula for current density.

[00:42:57]So one check one check here.

[00:43:02]Check the relation.

[00:43:28]Is it clear or not?

[00:43:32]Okay.

[00:43:34]So next one.

[00:44:26]So now we will discuss about okays.

[00:44:32]Let's discuss about.

[00:44:42]So, ohms law is nothing but the potential difference across the ends of the given metallic conductor.

[00:44:50]The potential difference across the ends of the given metallic conductor is directly proportional to current flowing through it. Is directly proportional to current flowing through it. So, I'm taking this resistor. So, across across we are connecting voltmeter.

[00:45:11]So current is flowing like this.

[00:45:15]Okay. So the potential difference the potential difference across the ends of the given metallic conductor is directly proportional to current flowing through it. V is directly proportional to I. V= I V = I. So what is R? R is the resistance.

[00:45:38]R is the resistance.

[00:45:41]understood or not? So this is very very important. Oh gives the definition of resistance. Ohmssila gives the definition of resistance. So very very important. So we will remember this point. So based on the resistance there are so many points we have to discuss.

[00:45:59]So R= V by I R= V by I is it clear or not? So next we will discuss about activity ohms activity we'll discuss ohms activating right so for that first materials required what are the materials required materials required materials required materials what are the what are the materials required for this first Four cells.

[00:46:38]Four cells 1.5 volt of each.

[00:46:43]And coming to the next one, nicro wire.

[00:46:49]Nicro wire of length 0.5 m length. Coming to the next one.

[00:46:57]Ameter voltmeter.

[00:47:00]ameter.

[00:47:05]So, fourth one voltmeter and the fifth one switch and the sixth one connecting wires.

[00:47:25]Okay. So, these are the materials required once again observe. So four cells. So 1.5 volts of each nikrome wire ammeter voltmeter switch connecting wires. Understood enough. So now we'll draw the circuit diagram. We'll draw the circuit diagram.

[00:47:48]Circuit diagram.

[00:48:14]So circuit diagram see four cells 1 2 3 4 a meter.

[00:48:33]So resistor switch to take here is a switch.

[00:49:24]Okay. So first one you have to connect one cell.

[00:49:31]First you have to connect one cell and note down reading of amter and voltmeter. First you have to connect one cell. Okay. So I have to connect one cell, one cell and wrote down the reading of ammeter and voltmeter.

[00:49:46]Ameter and voltmeter. Next one you have to connect two cells. Second one two cells you have to connect.

[00:49:55]Two cells you have to connect and note down the reading of a voltmeter. Two cells you have to connect and note down the reading of amter and voltter. meter and voltmeter. Coming to the so three and four. Repeat the same process.

[00:50:15]Repeat the same process for three and four. Understood or not? You have to connect you have to connect the cells.

[00:50:22]So first one, first you have to connect one cell. One cell you have to connect and note down the reading of a voltmeter. Second you have to connect to two cells. You have to connect to two cells. Again note down the reading of a ter and voltmeter and repeat the process for three and four. Repeat the process for three and four. Understood or not?

[00:50:43]After that you have to observe the reading of a and voltmeter. Okay. So those values you have to note down in the table column. So I'll drawing table column.

[00:50:57]So how to draw the graph?

[00:51:07]So table column you have to draw. So this is a table column.

[00:51:13]This is a table column like this.

[00:51:18]Serial number of cells am reading ultimate reading V by So serial number of cells omit reading ultimate reading V by that is R.

[00:51:37]So 1 2 3 and 4 1 2 3 4 1 2 3 4 Is it clear or not? So you have to observe the reading of amter and voltmeter. Ameter and voltmeter and mention in the table column mentioned in the table column. If you draw the graph, If you draw the graph for V and I. If you draw the graph for V and I. So you can see the graph I'm taking here. V on Yaxis I on X-axis. V on Yaxis I on X-axis. The graph is straight line. The graph is straight line for omic conductors. So what do you mean by omic conductors? The conductors which obey Ohm's law, the conductors which obey Ohm's law, those are called omic conductors. Okay. So the conductors which does not obey Ohm's law, those are called nonomic conductors. The conductors which obey Ohm's law, those are called omic conductors. For omic conductors, the graph is omic conductor.

[00:52:51]Omic conductors the graph is straight line. For nonomic conductors here you can see the graph is curve for nonomic conductors the graph is curve understood or not we on yaxis I on x-axis nonomic conductors nonomic nonomic conductors is it clear or not so what do we mean by omic conductors the conductors which obey Ohms those are called omic conductors. The conductors which does not obey Omla those are called nonomic conductors. The graph for nanomic conductor is curve. The graph for omic conductor is straight line. Is it clear or not? Yes. So now we'll discuss purely about resistance.

[00:54:04]Okay. So now we'll discuss about uh resistance.

[00:54:09]Okay. So after that we briefly discussed about difference between resistance and resistivity. After the temperature dependence of resistance everything then resistors are connected in series combination resistors are connected in parall combination everything we'll discuss. So here you can see so point A and point B. So ameter next battery.

[00:54:40]So switch current is flowing like this.

[00:54:50]I here you can observe between A and B so I'm taking nicro wire okay nicro wire first case first case is nicro wire of length L and area of the cross-section A so you have to take nicroire of length L and area of the cross-section A you have to connect between A and B and observe the reading of amter. So nicro is nic.

[00:55:31]So necroire of length L and area of the cross-section A you have to place between A and B and observe the reading of a meter. Okay. Coming to the next one. So I'm taking the twice of the length. Okay. So twice of the length and area of the cross-section is same same nicroally same necroyal twice of the length and area of the cross-section A.

[00:55:58]So connect between A and B connect between A and B observe the reading of 1 m. And coming to the third one so here you can observe area of the cross-section is twice twice of the area of the cross-section length is same. So area of the cross-section is twice length is same and you have to connect between A and B and observe the reading of a meter.

[00:56:25]Observe the reading of ammeter and coming to the fourth case. So in these three cases we are using nikrome wire.

[00:56:34]Okay. So in the first three cases we are using nicro wire. Coming to the fourth case we are taking the copper wire instead of nicrow.

[00:56:45]So I'm connecting copper wire.

[00:56:47]Understood or not? Copper wire.

[00:56:50]Copper wire. Is it clear or not? So length is same as I'm considering as I'm taking.

[00:57:00]So in the first case, so length L and area of the cross-section is A. Length is same area of the cross-section is L.

[00:57:09]Area of the cross-section is A only.

[00:57:11]Okay. So you have to connect between A and B. Observe carefully. Once again I'm explaining. So first you have to take nicro wire of length L and area of the cross-section A. You have to connect between A and B. A and B. Observe the reading of a meter. And neire of twice of length and area of the cross-section is A. connect between A and B and observe the reading of a meter and a nicire of twice of the area of the cross-section and length is L same length but area of the cross-section is doubled okay how to take area of the cross-section is twice of the initial one then you have to connect between A and B observe reading of a meter and the last case in the last case that is fourth case instead of nikrome wire you are taking the copper wire means M you're changing the material. You're changing the material. Understood or not? In the first case, so in the if you compare between two first and second, in the first two cases, we are changing the length. If you compare between one and three, we are changing the area of the cross-section. If you compare between 1 and four, we are changing the material also. Understood? Three cases. One is length we are changing area of the cross-section we are changing and material also we are changing so we can conclude that so by connecting all these four cases between A and B so we can observe the amit reading that is current reading understood or not that is current okay amid reading is current okay so by observing all these point we can conclude that we can conclude that so resistance is directly proportional to length of the conductor.

[00:59:11]Resistance is directly proportional to length of the conductor. So like as you increase the length resistance increases as you decrease the length resistance decreases. So that is resistance is directly proportional to length of the conductor. Resistance is inversely proportional to area of the cross-section. Resistance is inversely proportional to area of the cross-section. So R is directly proportional to L by A. R is directly proportional to L by A. So R = into L by A. R equ= to row into L by A.

[00:59:54]So what is row resistivity? What is the resistance? What is L length? What is a area of the cross-section?

[01:00:03]Understood or not? So this the resistance resistance row is a resistivity.

[01:00:16]Resistivity R is a resistance.

[01:00:20]R is the resistance. Row is the resistivity. L is the length of the conductor. A is area of the cross-section. A is the area of the cross-section. So now we will discuss the difference between differences between resistance and resistivity.

[01:00:49]So now we will discuss about differences between resistance and resistivity.

[01:00:55]Okay. So here resistance resistance and your resistivity.

[01:01:10]Resistivity resistance depends on length of the conductor and area of the cross-section.

[01:01:17]But resistivity does not depend on length and area of the cross-section. Is it clear or not? Yes. So now you can see here R is directly proport R is inversely proport area. R is directly proport A by L. So by seeing the formula by observing the formula we can get to know the we can get to know the definition of resistivity. By observing the formula by seeing the formula we can get the formula. We can get the definition we can get the definition of resistivity. So resistivity is equal to resistivity is equal to resistance of the conductor per unit length and unit cross-sectional area. Once again resistivity is equal to resistance of the conductor per unit length and unit cross-sectional area. That's enough by observing the formula only we can get to know the definition of resistivity. So generally so we will get confusion between resistance and resistivity. So what is the resistance? What is the resistivity? But both vary. So it vary according to the temperature. It vary according to the nature of the material.

[01:02:51]But what is the definition of resistance and resistivity. So and one more thing resistance depends on length and area of the cross-section. Resistivity does not depend this side is does not depend on length and area of the cross-section.

[01:03:04]And that is nothing but physical dimensions. It depends on temperature and area of nature of the material. So I'll discuss now. So check here. And assign it is very important. Assign it resistivity is very important. Here and symbol.

[01:03:25]And here you can see resistance depends on temperature.

[01:03:32]temperature and the resistance depends on nature of the material, nature of the material.

[01:03:47]Okay, coming to the resistivity row = row = m² by m. So meter meter get cancel row = m.

[01:04:01]So very important assignment of resistivity is very very important.

[01:04:06]Okay. So remember this point very very important. So starmax starax star. Okay. The assign of resistivity is meter.

[01:04:27]So coming to the nature, resistivity depends on temperature also. Resistivity depends on temperature and the resistivity depends on nature of the material.

[01:04:44]Nature of the material.

[01:04:49]Is it clear or not? Just check once all the points. All the points on subserve.

[01:04:57]all the points once observe here. So resistance depends on length of the conductor.

[01:05:06]Resistance depends on area of the cross-section.

[01:05:11]Resistance R = L by A R and assignate of resistance is ohm symbol. Resistance depends on temperature. Resistance depends on nature of the material.

[01:05:23]Coming to resistivity row = a by l. Resistivity row = a by l.

[01:05:33]Understood or not? Row = by l. Sinate of resistivity is ometer and resistivity depends on temperature. Resistivity depends on nature of the material.

[01:05:47]Nature of the material. Is it clear or not? Yes. So next one.

[01:06:18]So now one more point I'll discuss that is temperature dependence of resistance. So resistance and resistivity depends on temperature. Anyway if you change the metal automatically get but how temperature dependence.

[01:06:37]So I'll give two points. Point number one.

[01:06:42]So as soon as you increase the temperature of the conductor, the free electrons in the conductor increases, those free electrons will move with a greater amplitude.

[01:07:01]So they'll move the greater amplitude.

[01:07:05]So then what happens?

[01:07:07]Immediately if the electrons are moving with greater amplitude what happens?

[01:07:13]Immediately resistance and resistivity decreases. Resistance and resistivity decreases.

[01:07:20]Conductivity increases.

[01:07:23]Resistance and resistivity decreases.

[01:07:26]Conductivity increases.

[01:07:28]And when electrons are moving the greater amplitude, right, they're moving the greater amplitude. Well done. Good job. Great.

[01:07:38]Extraordinary, marvelous, amazing, mind-blowing everything, right? When electrons are moving with a greater amplitude where they are moving in the conductor that two very less space then remaining charges are there. Okay. So conductor wall is there. Then what happens? Those electrons and remaining electrons also there. One electron will eat another electron. That electron will let another great if they are moving to greater amplitude. What happens? Keep on collisions will takes place. By that what happens? Resistance and resistivity increases.

[01:08:21]Conductivity decreases. Resistance and resistivity increases.

[01:08:26]conductivity decreases. So by this we can conclude that by this we can conclude that as temperature increases resistance and resistivity also increases.

[01:08:43]Right? Yes. So that's enough. Now we'll discuss about resistors are connected in series combination. Resistors are connected in parallel combination. Okay.

[01:08:55]Resistors are connected in series.

[01:08:59]Resistors are Resistors are connected in series.

[01:09:06]connected in series combination.

[01:09:15]Combination resistors are connected in series combination.

[01:09:22]Yes or no?

[01:09:24]Now 1 2 3 R1 R2 R3 across R1 V_sub_1 across R2 V_sub_2 across R3 V3 three.

[01:09:55]So amter now current is flowing here.

[01:10:05]Switch.

[01:10:19]Yes. Observe here if resistors are connected in series combination.

[01:10:25]If resistors are connected in series combination throughout the path current is same throughout the path current is same.

[01:10:35]Understood or not? So I s = I1 = I2 = I3 = I.

[01:10:45]Current is same. Current is same throughout the path. All right. But potential difference is different.

[01:10:54]Potential difference is different across R1 V_sub_1 across R2 V_sub_2 across R2 V3.

[01:11:03]Yes or no? So that's why from what is the potential difference? V = I from ohms V = IR yes or no. So, V S = V S = V_sub_1 + V_sub_2 + V_sub_3 V S = V_sub_1 + V S = V_sub1 + V_sub_2 + V_sub3 from law from law V= I that is that is I S = I1 1 + I R2 + I R3.

[01:11:55]Is it clear or not? So IR is equal to I R1 + I R2 + I R3.

[01:12:02]Right? So I'm taking I common.

[01:12:06]So I am taking common that is R1 + R2 + R3.

[01:12:17]So I get cancel RS = R1 + R2 + R3.

[01:12:27]Is it clear?

[01:12:30]So RS = R1 + R2 + R3. If n number of resistors are connected in series combination. So once again observe carefully. R1 R2 R3 connected in series combination. So across R1 across R1 V_sub1 across R2 V2 across R3 V3. So current is flowing like this. So V = V1 + V_sub_2 + V3. I= I1 + I2 + I3.

[01:13:02]I I get I taking common I get cancel RS= R1 + R2 + R3. So RS = R1 + R2 + R3.

[01:13:11]Understood or not? Yes. So if n number of resistors are connected in series combination if n number of resistors are connected in series combination the time the time rs = nr rs = nr understood or not? So just check once.

[01:13:35]If n number of resistors are connected in series combination then RS equal to.

[01:13:59]Okay.

[01:14:01]So, observance.

[01:14:04]Observe once. Is it clear or not? Check once.

[01:14:10]Is it clear or not?

[01:14:14]So, if you have any doubts, you can ask me.

[01:14:18]So, I hope So if n number of resistors are connected in if n number of resistors are connected in If n number of resistors are connected in series combination, if n number of resistors are connected, so RS = NR RS= NR, Right.

[01:15:45]So I hope it is very clear. Just check once.

[01:15:50]So across R1 V1 across R2 V2 across R3 V3. So I= I1= I2= I3 I because throughout the path current is same throughout the path current is same.

[01:16:04]That's why V equal to V_sub_1 V_sub_2 V_sub3 because potential difference is different across V1 across R1 V1 across R2 V2 across R3 V3. So V= V1 + V2 + V3.

[01:16:18]So I R= I R1 + I R2 + I R3. So that's why so I'm taking I get cancel RS= R1 + R2 + R3 right? So I hope it is very clear. So coming to the next one, resistors are connected in parall combination.

[01:16:37]Resistors are connected in parall combination. So let's discuss about it.

[01:16:58]So parall combination Okay, resistors are connected in parallel combination.

[01:17:16]Then how it will be? We'll see.

[01:17:19]So I'm connecting like this. 1 2 3 a meter.

[01:17:58]R1, R2, R3 across R1, R2, R3. So I'm connecting voltmeter here.

[01:18:08]This is a voltmeter.

[01:18:14]So understood or not? So I'm connecting voltmeter across R1, R2, R3.

[01:18:22]Now current is different right? I1 I2 I3 I1 I2 I3 current is different through R1 I1 through R2 I2 through R3 I3 current is different. So potential difference is same. Potential difference is same.

[01:18:49]Current is different from Ohm's law V = I. So I = V by R. Right.

[01:18:58]So what is the Ohm's law formula? V = I = V by R. So then so VP = V_sub_1 = V_sub_2 = V_sub3 = V. So then I we have to take current current.

[01:19:19]Then IP IP = I1 + I2 + I3.

[01:19:31]I = I1 + I2 + I3.

[01:19:36]Understood or not? I = I1 + I2 + I3.

[01:19:42]Is it clear? Now shall I write V by RP = V by R1 + V by R2 + V by R3. So I'm taking V common 1x rp = v I'm taking common 1x r1 + 1x r2 + 1x r3 so v get cancel v get cancel understood or not so then can we take 1x rp = 1x r1 + 1x r2 2 + 1 by R3.

[01:20:32]Yes or no?

[01:20:37]If n number of resistors are connected in parall combination.

[01:20:42]If n number of resistors are connected in parallel combination to generally 1x rp = n by r = r by n.

[01:20:57]Okay.

[01:20:59]So rp = r by n.

[01:21:06]So that's enough.

[01:21:10]So this about resistors are connected in parall combination.

[01:21:16]Resistors are connected in series combination. All the point once again observe parall combination.

[01:21:23]So I'm taking R1 R2 R3. Okay. R1 R1 R2 R3 connected in parall combination.

[01:21:32]Okay. All one ends one side. all another ends one side. So what is connected at the ends like like this.

[01:21:47]So amter connected.

[01:21:50]Yeah, amter is connected. So current is passing. Now we can see potential difference is same across R1, R2, R3.

[01:22:00]Potential difference is same. Then IP equal to current is different I1 I2 I3 through R1 I1 through R2 I2 through R3 I3 current is different. So IP= I1 I1 + I2 + I3. So V by RP= V by R1 + V by R2 + V by R3. Is it clear or not? So now V I'm taking common then final answer 1x RP= 1x R1 + 1x R2 + 1x R3. So if n number of resistors are connected in parall combination if n number of resistors are connected in parall combination 1x rp= n by rp= r byn is it clear or not yes so that's enough this is about resistors are connected in par combination resistors are connected in parallel combination right yes so next So next one we will discuss generally.

[01:23:42]So all resistors cannot be uh reduced into simple series and parall.

[01:23:50]Okay. So all circuit cannot be reduced into simple series and parallel. Some circuit will be uh not able to reduce that time or deduct or solve or simplify. Okay, we can take any word. Now you uh if you are not able to do in series and parallel then we have to follow the kit laws.

[01:24:18]We have to follow the kit of laws. So here there are two laws are there. One is junction law, another one is loop law. So what is junction law? So junction law is nothing but kov loss.

[01:24:34]One is junction law.

[01:24:41]Second one is loopla. So junction law first I'll discuss later I will discuss about loopla. Okay. So k of last two one is junction another one is loop. Okay.

[01:24:53]First I'm discussing about junction law later we'll discuss about loop. So here you can see the algebraic sum of all the currents meeting at a junction equal to zero.

[01:25:06]Okay. So I1 I2 I3 and I4. So here you can see currents reaching to the junction equal to current leaving from the junction.

[01:25:23]Current reaching to the junction is equal to current leaving from the junction. So that is I1 + I2 = I3 + I4.

[01:25:36]The algebraic sum of all the currents reaching at a junction equal to zero. So this is a this is the first law of kit kit's first law. So coming to the junction loop law. Now we are talking now we are talking about junction law.

[01:25:52]So next one we are going to discuss about loop law. So what is loop? Okay.

[01:25:57]So in a closed enclosure in a circuit we are today we are taking one path in a closed path.

[01:26:13]So here you can see loopla. Second one is loopla loopla. Here four points you have to follow. Four points are to follow. So one is related to electromotive force that is cmf of the cell. So here sir uh we are to discuss about electromotive force. What is electromotive force? So maybe we'll get an we'll get doubt on it right. So I'll explain electromotive force then we'll go to the loop. So electromotive force is simple very easy only. So I'm taking the resistor like this like a cell and a resistor.

[01:27:03]So current anyway switch I'm taking. So if you want ameter okay positive terminal current is flowing like this.

[01:27:17]So normally when you on the switch when you on the switch what happens current will pass from positive terminal to negative terminal. We know that. Okay.

[01:27:29]When you on the switch immediately current will pass from positive termal to negative terminal. So positive charge that is a positive charge positive charge is moving from positive terminal to negative 10. So what about the charges there at negative 10 low potential. So who is doing work to bring positive charge from low potential to high potential from negative 10 to positive term.

[01:27:56]The work done to bring you need positive charge from lower potential to higher potential. The worker done to bring you need positive charge. So low potential to high potential. So positive charge at low potential in the cell within the cell. So the work done to bring unit positive charge from low potential to high potential from negative terminal to positive terminal from negative terminal to positive terminal. That is called electromotive force. The influence that makes the positive charge to move from positive negative terminal to positive terminal. The work done to bring unit positive charge from negative terminal to positive terminal is called emf electromotive force. So equal to = w by q v = a by q. So I hope you know we know that now. So emf is nothing but electromotive force. So of the cell of the cell okay work done by the cell or battery to move unit positive charge from negative terminal to positive terminal.

[01:29:08]Okay. So next coming to Loopla. Now you can see now we are taking yes loopla and a junction correct. So that only current and voltage. So loopla we are taking kov loopla kov kov loopla. So the point number one so you are moving through the across the cell from this the path path is very important in which direction you are moving in which direction you are moving that is very very important understood or not in which direction you are moving that is very very important so across the cell so here you are taking positive terminal negative terminal the emf of this cell is negative Because we are moving from ne positive to negative.

[01:30:11]So finally in which point you are reaching? Finally to which point you are reaching that is very important. Okay.

[01:30:18]So that point you have to take you are moving from positive to negative. So emf of this cell is negative. So coming to the next one. So you're moving from negative to positive.

[01:30:30]Negative to positive. The mf of this cell is positive. emf of this cell is positive. Coming to the next one, this resistor.

[01:30:40]Resistor. So R and I. So you are moving along the current direction. You're moving along the current direction. So what are the IR term? I term is negative. So V = minus I. So coming to the fourth one. So resistor.

[01:31:04]So you're moving opposite to the current direction.

[01:31:08]So the path is like this. So the dotted line represent path path and a path.

[01:31:17]Okay. So path is very very important in which direction you are moving that is very very important. Understood or not?

[01:31:24]So here you can see this is the path. So you're taking the current is opposite to the path. Then I term is positive.

[01:31:43]Is it clear or not?

[01:31:49]So these are very very important. These four points these four points are to follow. Okay. So while solving the circuit diagrams with the help of kit of loss with the help of kit of loss is it clear or not very very important make sure that you are following all the points right so next So generally when electron is flowing when electron Elect when electron is moving in the conductor moving in the cell it is passing through the electrolyte it is passing through the electrolyte it experience some resistance it experience some resistance. When electron is passing through the electrolyte it experience some resistance. So that is called internal resistance.

[01:33:09]Normally outside we are connecting the bulb like a fan AC those are external resistance. So inside of the cell when electrons are moving it experience some resistance voltage drop will be there V = minus I understood or not so that is called internal resistance that is called internal resistance.

[01:33:36]So here I'm taking the cell resistance B and here I'm taking like this A. So we are moving in this direction.

[01:33:52]Okay. So path MF of this cell is positive along the current direction we are moving I term.

[01:34:00]So internal resistance we are donating with the small letter R. external resistance capital R. So I and internal resistance R. The potential difference A and B is E minus I R.

[01:34:17]Okay. So electromotive force emf is positive internal resistance because we are moving in the same direction of current. Is it clear or not? Yes.

[01:34:34]Right. Yes. The next one.

[01:34:47]So we'll discuss about heating effect of electric current. So we'll discuss about heating effect of electric current.

[01:34:56]Okay. So let's discuss about it. Heating effect of Heating effects of electric current.

[01:35:07]Heating effects of electric current.

[01:35:16]So that is V = W by Q W = VQ as I said. So in the starting or in the previous concepts I mentioned one thing the potential difference potential difference is nothing but work done to bring unit positive charge from one point to another point within the conductor. Potential difference is nothing but work done to bring unit positive charge from one point to another point within the conductor. V = by Q. V= W by Q. Understood? So V = W by Q= VQ P = W by T. So we know rate of flow of charge. What is the rate of flow of charge? Electric current. What is the rate of flow of charge is called electric current? Q byt is I. Q byt is I. So P W = VQ by T that is P = V into Q byt is I. So P = VI P = VA. So then electrical energy electrical energy equal to P into T. So to find the electrical bill. So to find the electrical bill that time. So we'll use equal to P into T. So number of elements also we have to note down like N into P into T. So power they will give time they will give sometime they will give in hours sometime they will give in minutes so you have to convert sometime they will give like that so understood or not so you have to you have to convert into hours right now we can see uh P = what VA whatever the energy is given to the conductor that will become in the form of heat whatever the energies given to the conductor that will become in the form of heat so T I into T we know V = I V = I understood or not? So substitute in the place of V. So v = I then you can take now h = I into I into t then you'll get h = i² rt.

[01:37:46]Heat produced in the conductor.

[01:37:50]Okay. Heat produced in the conductor is directly proportional to square of current. Heat produced in the conductor is directly proportional to resistance.

[01:37:59]Heat produced in the conductor is directly proportional to time. So I hope it is very clear. So this is about heating effect of electric current.

[01:38:09]Heating effect of electric current.

[01:38:11]Right? Yes.

[01:38:33]So now we will discuss about it.

[01:38:37]Now we'll discuss about Yeah. Correct only Manish Kumar H= I² RT that is true now we'll discuss about cells are connected in series cells are connected in parallel right cells are connected in series cells are connected in parallel so let's discuss about it Cells are connected in series.

[01:39:32]Okay. cells are connected in series. Now you can see here Okay.

[01:40:20]Net emf. Net emf equal to net emf.

[01:40:29]Net emf = to any net internal resistance net internal resistance equal to nr.

[01:40:47]External resistance equal to external resistance is capital R and the total resistance equal to total resistance that is equal to NR + R.

[01:41:13]Then I = net emf by netf by total resistance that is what is netmf ne what is net total resistance n r + r Is it clear or not?

[01:41:49]Just check once.

[01:42:01]So this is about cells are connected in series. Now we'll discuss about cells are connected in parallel.

[01:42:09]Cells are connected in parallel.

[01:43:42]Okay.

[01:43:43]So now you can see here cells are connected in parall combination.

[01:43:50]Net emf.

[01:43:55]Net emf is a net internal resistance.

[01:44:03]Net internal resistance.

[01:44:09]It's actually n / r r by n uh total resistance total resistance is capital R or sorry external resistance. This is external resistance.

[01:44:34]external resistance.

[01:44:39]Now total resistance total resistance is R + R by N.

[01:44:53]So I = to net emf by net or net total resistance total resistance I I'm writing total resistance.

[01:45:20]So that is I = to E by R + R by N.

[01:45:35]So this about cells are connected in parallel combination.

[01:45:40]Cells are cells are yes these are emf is equal resistance also equal that's why okay equal I'm taking difference also you can take and do it okay so that's enough few problems we'll discuss So related to current we'll do few problems. Okay let's discuss.

[01:47:19]Okay, let's do one problem.

[01:47:25]They're doing Okay.

[01:48:36]Can you solve this question?

[01:48:43]Very simple. Vas only. Try to solve this one.

[01:49:46]So what the answer to this question?

[01:49:49]Anyone knows the answer? Let me know.

[01:50:28]So answer is so resistance given current is given or time is given R = 20 ohm I = 5 5 A time = 30 second then H = I² RT H= I² RT we can Follow right?

[01:51:00]H= I square R we can follow. So now uh 5 square uh 20 30 how much?

[01:51:24]So let me know the answer.

[01:51:27]15 or sorry 15 15 correct only.

[01:51:38]Yes J heat right.

[01:51:43]So thank you so much for joining attending and listening.

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