The Solid State

Question 169

Explain the following with suitable examples:

Ferromagnetism: few substances like iron, cobalt, nickel, gadolinium and CrOare strongly attracted by a magnetic field. Such substances are known as ferromagnetic substances. These substances can be permanently magnetised with the help of strong electrostatic field.  The metal ions of ferromagnetic substances are grouped together into small regions called domains in solid state. So that each domain acts as a tiny magnet. The domains of  un magnetized piece of a ferromagnetic are randomly oriented so that their magnetic moments get cancelled out. When such substance is placed in a magnetic field, all the domains get oriented in the direction of the magnetic field  and a strong magnetic effect is produced. This ordering of domains remains same  even when the magnetic field is removed and the ferromagnetic substance becomes a permanent magnet.

Fig.  Schematic alignments of magnetic moments in ferromagnetism.

Question 170

Explain the following with suitable examples:


few substances like O2, Cu2+, Fe3+, Cr3+  are weekly attracted by a magnetic field.
These substabces are magnetised in a magnetic field in the same direction. When we remove magnetic field ,they lose their magnetism. paramagnetism is takes place due to presence of one or more unpaired electrons. These unpaired electron are attracted by the magnetic field.
Question 171

Explain the following with suitable examples:


This effect is observed when the magnetic moments of the domains in the substance are aligned in parallel and anti–parallel directions in unequal numbers. Ferrimagnetic substances are weakly attracted by magnetic field as compared to ferromagnetic substances. Magnetite like Fe
3O4  and ferrites like MgFe2O4 and ZnFe2O4 are examples 

Question 172

Explain the following with suitable examples:
Piezoelectric effect (or pressure electricity)


Piezoelectric effect (or pressure electricity):
The word piezoelectricitymeans electricity resulting from pressure.
Insulators do not conduct electricity be the electrons present in them are held tightly to the individual atoms or ions and do not move. However, when an electric field is applied polarisation takes place and newly formed dipoles may align themselves in an ordered manner so that such crystals have a net moment.
When mechanical stress is applied on a polar crystals so as to deform them, electricity produced due to displacement of ions. This is known as piezoelectric effect and electric so this produced is known as Piezo electricity or pressure electricity. Example are : titanium, barium and lead, lead zirconate (PbZrO3), ammonium dihydrogen phosphate and quartz.

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