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BH Curve

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Published in: Physics
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BH Curve

Durga S / Chandigarh

4 years of teaching experience

Qualification: M.Sc (d.a.v college - 2017)

Teaches: Chemistry, Mathematics, Physics

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  1. MAGNETIC FIELD AROUND A CONDUCTOR When a current is passed through a conductor it modifies a space around it i.e. Magnetic field is produced Current Carrying C on du ctor Convention al Compass Needle Electron Paper Electr omagn etic Field (Clockwise) Co nventional Lines of Magnetic Electron FIO'W Electromagnetic Field (Anti clockw ise Fig. 1.1 Magnetic Field around a conductor
  2. TERMINOLOGY MAGNETIC INTENSITY:- For magnetic field Bo in the vaccum MAGNETIZATION:- Units-A/m Magnetic moment per unit volume , given by- Units-A/m M =magn. mom/V MAGNETIC INDUCTION:- Sum of magnetic field Bo and magnetic field gol produced due to magnetization of substance- MAGNETIC SUSCEPTIBILITY:- Units-Tesla Measure of aptness to acquire magnetism , given by x = M/H MAGNETIC PERMEABILITY:- Measure of conducting power towards passage of magnetic lines of induction , given by Units-Tm/A
  3. MAGNETIC DOMAINS A magnetic domain is a region within a magnetic material in which the magnetization is in a uniform direction. This means that the individual magnetic moments of the atoms are aligned with one another and they point in the same direction. Fig.1.2 Arrangement Magnetic Domains in materials
  4. MAGNETIC SUBSTANCES All the substances are magnetised when placed in a magnetic field, however the behaviour of different substances is different in an external magnetic field. Thus the substances are divided into three classes:- Diamagnetic Substances. O Paramagnetic Substances. O Ferromagnetic Substances. O The properties of the each of the described substances are as discussed further.
  5. DIAMAGNETIC SUBSTANCES These are the substances which in strong external O magnetic field, acquire a feeble magnetism opposite to the direction of applied magnetic field. O O cccno cccio O O O O O Repelled feebly by a magnet. No unpaired electrons in them. They do not obey Curies Law M has slightly negative value. has small negative value. o cccco Relative permeability(gr) is less than I o cccco Fig1.3 Alignment of domains in Diamagnetic on applying B Examples of Diamagnetic Substances:- Copper(Cu), Silve(Ag), Gold(Au), Antimony(Sb), etc
  6. O O O O O O O O PARAMAGNETIC SUBSTANCES These are the substances which when placed in a strong magnetic field acquire a feeble magnetism in the same direction as the applied magnetic field In Absence of Magnetic Field In Presence of Magnetic field Attracted feebly by the magnet. Unpaired electrons are present in them. They follow Curiexs Law- =C/T M has slightly positive value. is slightly positive. Relative permeability(gr) is slightly positive. Examples of paramagnetic substances are:- Aluminium(Al), Sodium(Na), Platinum(Pt) Manganese(Mn), etc Paramagnetism Fig1.4. Alignment of Domains in Paramagnetic on Applying B
  7. O O O O O O O O FERROMAGNETIC SUBSTANCES These substances are those which acquire strong magnetism in the direction of applied magnetic field. Attracted strongly by the magnet. In Presence of Magnetic Field These have randomly oriented domain In Absence of Magnetic Field They do not obey Curiexs law. M has large positive value. has large positive value. Ferromagnetism Fig. 1.5 Relative permeability(gr) has large positive value. Alignment of Domains in ferromagnetic on applying B Examples of the ferromagnetic materials are:- Iron(Fe), Cobalt(C0), Nickel(Ni) steel, etc
  8. DURING THE PROCESS OF MAGNETIZATION THERE ARE Two TYPES OF LOSSES:- •Hystersis loss •Eddy Currents losses
  9. HYSTERSIS The lagging of magnetic induction x BX or intensity of magnetisation NM x behind the magnetising force NH producing it when a ferromagnetic material is taken through a cycle of magnetisation.
  10. HYSTERSIS LOOP B Flux Density Retentivity Saturation Magnetizing Force Coercivity Magnetizing Force In Opposite Direction Saturation In Opposite Direction Flux Density -B In Opposite Direction Fig 1.6 B-H loop
  11. DESCRIPTION OF LOOP At O,H=O and M=0,when H increases , M also increases O till a, i.e. saturation point. Decrease H,M decreases slowly . At b , H=O but B has O some value , known as remanence or retentivity. Decreasing H in negative value, at c, B=o but H has a O negative value, known as coercivity. Further decreasing H , saturation point is again reached O at d. Now decrease H to zero , we get point e, at which again O Now on increasing H,the cycle is repeated back and we O reach at point a. Closed curve abcdefa is hystersis curve. O
  12. HYSTERSIS LOOP The graph showing how M or B increases with H O from zero to maximum in one direction and then back through a zero to a maximum in opposite direction and finally back again through zero to the first maximum. The area under the curve gives the energy loss O Fig1.7 B-H Curve Circuit Globe
  13. CALIBRATION Calibration is the process of configuring an instrument to O provide a result for a sample within an acceptable range. Eliminating or minimizing factors that cause inaccurate measurements is a fundamental aspect of instrumentation Here we calculate calibration constants and hence O retentivity and coercivity.
  14. COMPARISON Steel is better for permanent magnets than soft iron since O the retentivity of the iron is little greater than that steel is completely outweighed by its much smaller coercivity which makes it easy to demagnetise. Soft itm B) Steel Fig1.8 B-H Curves for soft Iron and Steel
  15. CONCLUSIONS Electric coercivity, is the minimum external electric O field required to destroy the residual magnetism is called the coercivity. Retentivity is the value of intensity of magnetisation O retained by the ferromagnetic substance when the magnetising field is switched off. Materials used to make permanent magnets should O have high value of retentivity and coercivity. Material used to make electromagnets high retentivity O and low coercivity

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