5. Answer any two of the following items. You may include equations if you want,
ID: 1769845 • Letter: 5
Question
5. Answer any two of the following items. You may include equations if you want, but do not derive them. You may answer in point form if you wish but be sure to make your answers clear, relevant and sufficiently detailed to answer the question. (a) Briefly describe the difference in properties between polar and non- (b) Briefly explain how one can use the Hall effect to demonstrate that the (c) Briefly describe the difference between paramagnetism and diamag- polar dielectrics, and the meaning of the term "polarizability". charge carriers in a metal are negatively charged. netism (d) Briefly describe what is meant by the “displacement current" term in Ampere's Law as modified by Maxwell, and why it is necessary to include this term (8 marks)Explanation / Answer
Answer a)
POLAR DIELECTRICS
Polar dielectrics/polar molecules, these are molecules whose positive and negative centers are separated and hence have an intrinsic permanent dipole moment.When an electric field is applied, the dipoles are oriented by rotation and aligned in the direction of the electric field so that one type of bound charges (+ve or -ve) appear on one surface and the opposite type on opposite surface. Example of polar dielectrics are water, ammonia
NON POLAR DIELECTRICS
In non polar molecules, the centers of the positive and negative charges coincide with each other and hence has no intrincisc dipole moment. But when an electric field is applied, the electron cloud is slightly distorted because the positive and the negative charges get attracted in the opposite directions thus giving rise to some induced polarisation. Examples: Carbon dioxide molecules, H2
Under the effect of an external electric field, when either a polar or a non polar dielectric develops a net dipole moment, this dipole moment per unit volume is called polarizibility. For isotropic linear dielectrics
P = E, dipole moment is P. is polarizibility, E is the electric field
Answer C)
PARAMAGNETISM / PARAMAGNETIC MATERIALS
This is exhibhited by those materials whose atoms have unpaired electrons in their partially filled oribitals. Under the action of an external magnetic field, the magnetic moments of these unpaired electrons, partially align in the same direction as that of the field thus producing a net positive magnetization and a positive susceptibility. Most common examples are iron bearing minerals.
DIAMAGNETISM/DIAMAGNETIC MATERIALS
These are materials whose atoms have no unpaired electrons. Thus these atoms have no intrinsic magnetic moments. But under the action of an external magnetic field the induced magnetization is negative and thus even is the susceptibility. Diamagnetism is a property which is weakly present in almost all types of materials. Examples: Quartz, calcite.
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