Plus Two Physics Chapter Wise Previous Questions Chapter 5 Magnetism and Matter is part of Kerala Plus Two Physics Chapter Wise Previous Questions and Answers Kerala. Here we have given Plus Two Physics Chapter Wise Questions and Answers Chapter 5 Magnetism and Matter.
Kerala Plus Two Physics Chapter Wise Previous Questions and Answers Chapter 5 Magnetism and Matter
The B – H curve of a ferromagnetic material is as shown in figure:
a. What do you mean by ferromagnetic material? Write any two properties of it.
b. Identify the values of retentivity and coercivity from the figure.
c. A solenoid has a core of a material with relative permeability 400. The windings of the solenoid are insulated from the core and carry a current of 2A. If the number of turns is 1000 per metre, calculate magnetic – intensity (H) and magnetic field (B). [March-2018]
a. Ferromagnetic substances are those which gets strongly magnetised when placed in an external field. They get strongly attracted to a magnet.
They have high susceptibility
b. Retentivity – ob
Coercivity – oc
c. H = nl = 1000 x 2 = 2000 A/m
Explain hysteresis and draw hysteresis curve for a ferromagnetic substance. [March-2017]
The relation between B and H in ferromagnetic materials is complex. It is often not linear and it depends on the magnetic history of the sample.Figure depicts the behaviour of the material as we take it through one cycle of magnetisation. Let the material be unmagnetised initially. We place it in a solenoid and increase the current through the solenoid. The magnetic field B in the material rises and saturates as depicted in the curves Oa.
This behaviour repressent the alignment and merger of domains until no further enhancement is possible. It is pointless to increase the current (and hence the magnetic intensity H) beyond this. Next, we decrease H and reduce it to zero. At H = 0, B≠0.This is represented by the curve ab. The value of B at H = 0 is called retentivity or remdnence.
In Fig BR~1.2 T, where the subscript R denotes retentivity. The domains are not completely randomised even though the external driving field has been removed. Next, the current in the solenoid is reversed and slowly increased. Certain domains are flipped until the net field inside stands nullified. This is represented by the curve be.
The value of H at c is called coercivity. In Fig. As the reversed current is increased in magnitude, we once again obtain saturation. The curve cd depicts this. The saturated magnetic field Bs~ 1.5 T. Next, the current is reduced (curve de) and reversed (curve ea). The cycle repeats R itself. Note that the curve Oa does not retrace itself as H is reduced.’ For a given value of H, B is not unique but depends on previous history of the sample. This phenomenon is called hysterisis. The word hysterisis means lagging behind.
a. State Gauss’ law for magnetism.
b. How this differs from Gauss’ law for electrostatics ? [March-2016]
c. Why is the difference in the two cases ?
a.Gauss’s law for magnetism states that the net magnetic flux through any closed surface is zero, i.e.,
b. Gauss’s law in electrostatics states that the total flux through a closed surface is 1/ε0 times the net charge enclosed by the closed surface.
c. Because magnetic monopole does not exists, magnetic field lines forms closed path, net flow is zero in magnetism and net flow is q/ε0 in electrostatics for closed surface.
i. Permanent magnets should have
a. high retentivity and low coercivity
b. low retentivity and high coercivity
c. high retentivity and high coercivity.
d. low retentivity and low coercivity.
ii. Distinguish between para, ferro and diamagnetism. [March-2015]
i. c. high retentivity and high coercivity.
Paramagnetism. Feebly magnetise along applied field.
Diamagnetism : Feebly magnetise opposite to magnetic field.
Ferromagnetism : Strongly magnetise along magnetic field
A bar magnet free to rotate in a vertical plane aligns itself with its axis vertical at a certain places on earth.[Model-2014]
a. What are the values of dip and horizontal component of earth’s magnetic field at the place?
b. Name the magnetic element of earth which is not mentioned here.
a. Dip is the angle between magnetic field and horizontal component of magnetic field. Angle of dip will have more value at northern hemisphere than southern hemisphere. The value of horizontal component depends on the total field strength and angle of dip.
b. Declination is the angle between Magnetic Meridian and Geographic meridian.
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