NEET Physics by SufalPhysicsForum - Dailymotion

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00:00Then here comes, before doing theory law, I discuss very small comparison between diapera

00:13and ferro.

00:14Actually, now I am to cover up thorough comparison between these three types of magnetic materials.

00:28For your purpose, already I have arranged very important screenshots.

00:35Some I am to discuss here and some more I will be sharing while doing video editing.

00:44Let us come to these four screenshots first.

00:48Here firstly, behavior.

00:52In context to behavior, in non-uniform magnetic field, how these three types of magnetic materials

01:00behave.

01:01It moves from stronger to weaker magnetic field.

01:05See north and south, pole, strength, diamagnetic substances are going away.

01:14It completely went away from pole strength, whereas paramagnetic, now see, they have accumulated

01:25towards pole strength, very close.

01:29Then ferromagnetic, strongly they have approached towards pole strength.

01:35Then this was weak field, now strong field, again they went away.

01:42Strong field, they have accumulated near to stronger field and here strongly, stronger

01:51accumulation because of ferromagnetic.

01:55Then after that, when we have any diamagnetic liquid in U-tube, then this diamagnetic liquid

02:06will be, will have tendency to go away from the stronger field, whereas for paramagnetic

02:16substances, now this liquid is approaching towards stronger field, right?

02:25Then chi-m-t curve, that means graphical analysis, criteria of comparison is graphical analysis

02:35between susceptibility to temperature.

02:40For diamagnetic, it is simply straight line, that means it is independent.

02:49Here for paramagnetic substances, susceptibility is inversely proportional to temperature.

02:55We have already read this law under the Heading Curie law for paramagnetic.

03:02Then for ferromagnetic, again chi-m is inversely proportional to temperature only, provided

03:12this T-c line is the barrier, that means, in this region, there is no variation beyond

03:27this T-c only, this analysis.

03:31And remember, this T is absolute temperature in both these situations and T-c was Curie

03:38temperature.

03:41Now fourth parameter, that is relative magnetic permeability.

03:46For diamagnetic, it lies between 1 and 0, right?

03:53Here for paramagnetic substances, permeability lies between 2 and 1 and here relative magnetic

04:09permeability is very large as compared to 1.

04:13Why?

04:14Because it has to demonstrate strong responses towards external magnetic field in which ferromagnetic

04:25substances are kept.

04:27For example, copper, nickel, cobalt, they have mu r in the order of 1000, 2000, 3000,

04:354000 like this.

04:37And fifth parameter, magnetic moment of single atom.

04:44Atoms do not have any permanent magnetic moment.

04:47This magnetic moment we discussed under the heading Bohr magneton.

04:53If you remember, we analyzed mathematically that M is 1 by 2 e omega r square, right?

05:07If you want, I can show you, but this we covered in third video, we may not be able to access

05:15here.

05:16Yeah, we can't have because fourth video we started with.

05:21For the time being, you remember and so in context to that only, atoms do not have any

05:30permanent magnetic moment whereas atoms have permanent magnetic moment which are randomly

05:37oriented that is for paramagnetic and ferromagnetic again permanent magnetic moment which are

05:47organized in domains and next parameter when rod of material is suspended between poles

05:55of magnet, diamagnetic substance will be aligned like this perpendicular.

06:04That means they are not to support this strong magnetic field whereas paramagnetic will be

06:11aligning along this magnetic field and here ferromagnetic will be strongly aligning.

06:21And next magnetic moment of substance in presence of external magnetic field value

06:28M is very less and opposite to H and here value M is low but in direction of H. H means

06:39magnetic intensity or magnetizing force or magnetizing field.

06:45All the three are for same M is very high in for diamagnetic M was very less for paramagnetic

06:55M is low but in direction of H but here M is very high and in direction of H and these

07:03are the examples you can note it down for your reference.

07:10Second part is iron, cobalt, nickel all their alloys and then this GD is gadolinium and

07:20this is Elnico.

07:22So these are important and second last and last substances placed in uniform magnetic

07:31field.

07:32How do they respond when they are placed in uniform magnetic field?

07:38Here in case of diamagnetic they prefer not to not to let them enter all these field lines

07:46are trying to go outside but for paramagnetic a lot of magnetic field lines will be trying

07:56to enter through the paramagnetic while it is passing through the paramagnetic substance

08:03and paramagnetic they behave very friendly all the field lines are trying to go and pass

08:17through the paramagnetic substance only they prefer not to go out all the lines will try

08:26to enter through the paramagnetic.

08:43And last IH curve I means intensity of magnetization versus magnetic intensity small negative varies

08:55linearly with field this shows the graph is in fourth quadrant it shows it is negative

09:04but linear variation but for paramagnetic it is linear variation only but positive.

09:11What we could conclude negative that means they behave negatively towards external magnetic

09:19whereas paramagnetic behave positive and ferromagnetic they behave exponentially that

09:29means they are to respond very very positively towards external magnetic field.

09:36So in general we have discussed all even then I will be sharing few more screenshots when

09:46you will be going through the video.

09:55So very slight discussion what is hysteresis?

10:00Hysteresis let us first know what is in terms of definition what is hysteresis?

10:08Basically hysteresis is the variation of B and H it is the variation of B and H.

10:20B that means magnetic field induction H means magnetic intensity all together

10:29for any magnetic sample when it is subjected for magnetization and demagnetization.

10:41And what is the definition?

10:43Phenomenon of lagging of I or B behind H you would not be able to understand this

10:54language of definition unless and until I draw the diagram total graph.

11:01So wait for a while I am reaching behind H when a specimen of magnetic material

11:12subjected to a cycle of magnetization is called hysteresis.

11:21Lagging of I or B behind H now this is H max this was H ampere per meter this was

11:34here B that means Tesla this is H max from the diagram you could very easily observe

11:44that as H increases B also increases but proportionately as H increases B could not

11:57increase at that speed that means it is something is lagging otherwise graph could be

12:06like that also.

12:07But intentionally variation became curvy and because of this curvy thing in definition

12:18we had phenomenon of lagging of I or B behind H whether we consider I or B along

12:32along y axis and H along x axis when a specimen.

12:39So basically this whole graph is graphical variation between B and H magnetic field

12:51magnetic field induction and magnetizing force or magnetic intensity.

12:59Right and when any magnetic material is subjected to magnetization and demagnetization

13:08this whole graph talks about the cycle of magnetization and demagnetization.

13:16That means see it is process of as my cursor is going this is process of magnetization.

13:26Here now demagnetization process begin and it will be going till this point

13:39then after that again magnetization process starts.

13:44So this whole thing is studied under this graph now I am to discuss two two physical

13:53quantities namely residual magnetism or retentivity.

14:00For this I must mention the definition retentivity or residual magnetism.

14:11Residual magnetism means in the graph I am going to show you what is that

14:18what is that this bold blue line is residual magnetism or retentivity.

14:45Residual magnetism how do we define the value of magnetic induction

14:54B left in the specimen when the value of magnetic induction B left in the specimen

15:03when the magnetizing force is reduced to 0 is called retentivity of the material.

15:16Now I am going to explain in the graph let us see what our language says the value of

15:22magnetic induction B left in the specimen when the magnetizing force is reduced to 0 is called

15:29retentivity. Let us come to the graph C now if we want to decrease this H to 0.

15:42Let us see how variation proceeds as this graph is proceeding finally at this point

15:51where my cursor is static now H has become 0 and at this position still

16:00this much B is left that means in absence of any cause of external magnetic field

16:10still our magnetic sample consists of this much magnetic field even we have removed our

16:19source of external magnetic field might be there might be some strong magnets

16:26which we have removed for now that's why H has become 0 that is residual magnetism

16:34and for that only I have mentioned the definition so this was our keyword

16:42magnetizing force that means H is 0 then here comes coercivity for coercivity also

16:51now if we want to decrease this B also to 0 but then we need to apply from external source

17:03external magnetic field in opposite direction so this was positive H now negative H we need to

17:14impose and this much negative H is needed for decreasing this B to 0 now which color I should

17:27this green is coercivity that means negative value of H needed for decreasing this B

17:39to 0 now proper definition for coercivity value of magnetizing force in opposite direction

17:50to reduce the residual magnetism to 0 is called the coercivity negative H to reduce the residual

18:03magnetism to 0 then one more energy dissipation due to hysteresis energy dissipation during

18:15hysteresis basically this topic is similar to the resistor when any current is made to pass

18:26through the resistor then resistor offers some resistance and because of that resistance

18:33because of that obstruction heat is dissipated across the resistor same way when any magnetic

18:41material is subjected for magnetization then it also offers some resistance towards magnetization

18:52then then during magnetization some negligible amount of heat is dissipated

18:58and during demagnetization obviously heat should be absorbed so that is the point

19:07now I will be associating this fact while comparing soft iron and steel that means

19:17that means electromagnets and permanent magnets area of hysteresis loop is equal to the energy

19:29dissipation during magnetization and comparison of steel and iron.

19:38Iron means soft iron we are to think for now very interesting steel will have fat and bulky

19:49hysteresis loop why an iron will have very thin slim and trim this is what's the significance

20:01fat and bulky what's the significance behind this mu for soft iron and this is steel for soft iron

20:14mu r is maximum that means whenever this material is kept in uniform magnetic field

20:23or external magnetic field it absorbs maximum number of field lines more effectively vigorously

20:33without any effort so that means it it is offering least resistance towards magnetization

20:42and since it is offering least resistance that's why energy dissipation will be also very less

20:51that's why very slim trim and thin whereas on the other hand for steel its mu r is not that much

21:01high so it has to offer greater resistance towards magnetization hence it will be

21:11dissipating great amount of heat as compared to soft iron thereby fat and bulky and that

21:19is the reason of steel is used for permanent magnets whereas soft iron core is used for

21:30electromagnets so I am going to paste one screenshot having comparative study between

21:40permanent magnets and electromagnet salts that means what are the characteristics

21:45needed for permanent magnets and electromagnets respectively for that question purpose you may

21:54learn that table hence our discussion is has to be ended here only thanks for viewing and

22:05enjoying my video keep on working all the best see you in next video bye take care

22:27you

Magnetism & Matter 05 | Magnetic Materials | Hysteresis Curve #jee

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