B- H curve presentation..pptx

A detailed presentation on Magnetic Hysteresis including everything like experiments also.

1. Magnetic hysteresis

2. PRESENTATION ON B-H CURVE TOPICS-: Introduction MAGNETIC SUBSTANCES B-H CURVE SOME TERMS RELATED TO B-H CURVE APPLICATIONS OF B-H CURVE

3. INTRODUCTION B H Curve:- The BH curve is a plot of the Magnetic flux density(B) vs Magnetic field Strength(H). The curve tells us about the change in the flux density of a material as the magnetic field strength is gradually increased or decreased. The complete BH curve is usually described as a Hysteresis loop.

4. MAGNETIC SUBSTANCES All the substances are magnetized when placed in a magnetic field, however the behavior of different substances is different in an external magnetic field. Those substances can be divided into three classes:- Diamagnetic substances Paramagnetic substances Ferromagnetic substances Their properties are discussed further:-

5. DIAMAGNETIC SUBSTANCES Diamagnetic substances are those substances which are feebly repelled by a magnet. When placed in magnetic field , the lines of the force tend to avoid the substances. When placed in strong external magnetic field, they acquire feeble magnetism opposite to the direction of applied magnetic field. These have relative permeability (µ r ) slightly less than the unity. Susceptibility has small negative value. EXAMPLES- Copper, Silver, Gold , Bismuth etc.

6. PARAMAGNETIC SUBSTANCES Paramagnetic substances are those substances which are feebly attracted by a magnet. The lines of the force prefer to pass through the substances rather than the air. In strong magnetic field, they acquire a feeble magnetism in the same direction as the applied magnetic field. Relative permeability (µ r ) is slightly greater than unity. Susceptibility has small positive value. EXAMPLE- Aluminum,Oxygen , Platinum,Chromium etc.

7. FERROMAGNETIC SUBSTANCES Ferromagnetic substances are those substances which are strongly attracted by a magnet. The lines of the force tend to crowd into a specimen. These substances acquire strong magnetism in the direction of applied magnetic field. Relative permeability (µ r ) is much greater than unity. Susceptibility has large positive value. EXAMPLE- Cobalt , Nickel , Iron etc.

8. TERMINOLOGY MAGNETIC FIELD INTENSITY:- It is a measure of how strong or weak any magnetic field is. S.I. UNIT OF H:- Ampere/meter (A/m). MAGNETIC INDUCTION:- Capability of a material to induce the number of lines of magnetic field. S.I. unit of B- Tesla or Weber per meter square. FACTORS ON WHICH MAGNETIC INDUCTION DEPENDS ARE:- Permeability(µ) Susceptibility

9. PERMEABILITY :- It is the ability of a material to support the formation of a magnetic field within itself. In other words , it provides the permission to the magnetic lines of force to enter into the particular substances. In addition , Relative permeability (µr) is the ratio of the permeability of the material to the permeability of free space. SUSCEPTIBILITY :- It is the degree to which a material can be magnetized in an external magnetic field. In other words, its capacity to get magnetized when placed in magnetic field.

10. definition : Hysteresis means “lagging”. The lagging of intensity of magnetisation (B) behind the intensity of magnetic field (H). For unique value of H, I is not unique. I depends on history of sample

11. HYSTERESIS curve EXPLANATION : A graph is drawn between the intensity of Magnetization (B) and intensity of magnetic field (H). When the intensity of magnetic field H is increased from zero , the intensity of magnetism is also increased. Further increasing the value of H , the B value is also increased and finally reaches the saturation point A in figure i.e., B is constant. Then decreasing the value of H , the B value is also decreased. But at the point H=0 , But B is not equal to zero . Now the material retains some amount of magnetism is known as Retentivity ( or) Residual magnetism. ( point B in fig.)

12. Further decreasing the value of H in negative value , the B value is also deceased at point C the material is fully demagnetized . The force is required for remove the residual magnetism is called as Coercive force.( point C in fig.). The cycle is continue in opposite direction as shown in fig D is saturation point , E is retentivity and F is the coercive force in negative direction . The cycle is completed , it make the hysteresis loop.

13. Experiment Aim : To study the B —H curves for a given ferromagnetic material (iron) by the use of a cathode ray oscilloscope . Apparatus : An anchor ring of iron with primary and secondary coil windings on it, a resistance box (range 0-5000 ohm), a fractional resistance box (0 — 10 ohm), cathode ray oscilloscope, capacitor, tracing paper, graph paper etc.

14. Formula Used :- According to Steinmetz law the energy loss per cycle of magnetisation in a ferromagnetic material is given by: W=h(B max) k Here h is the Steinmetz coefficient and it is a constant whose value varies from material to material. The exponent k varies between 1.4 and 1.8 and for the various ferromagnetic material the accepted value of k is 1.6.

15. Circuit diagram:-

16. Observation: Calculate the area(a) of B-H curve by counting the number of squares inside the loop. Also measure the value of ( B max ) of the loop. Now plot a graph taking log(B max ) along X-axis and log(a) along Y-axis. The graph come out to be a straight line. The slope of this line is equal to k occurring in Steinmetz law. Result:( i ) The B-H loops drawn for the given Ferromagnetic material are enclosed herewith. (ii) The Steinmetz law for energy loss in hysteresis cycle is verified.

17. FACTORS AFFECTING THE HYSTERESIS LOSS:- Volume of the material. Area enclosed by the Hysteresis Loop. Area of Hysteresis Loss:- The hysteresis loss is directly proportional to the area under the Hysteresis Loop. For the loss material the Hysteresis Loop is narrow.

18. Which material is better for Permanent magnet? It should have:- i ) High retentivity ii)High coercivity iii)High permeability iv)Large area of Hysteresis loop Though soft iron has a bit large retentivity than steel yet due to other factors in which soft iron is for behind .Hence steel is a better choice. Which material is better for use in coil of generator or core of transformer? It should have:- i ) Low retentivity ii) Low coercivity iii) Small area of Hysteresis loop So, soft iron is better choice.

19. PRESENTED BY :- riya , ROLL NO :-22 vaishali , ROLL NO :-23 anjali , ROLL NO :-24