Shape memory effect It is the phenomenon in which the shape memory alloy apparently deforms at lower temperature and returns to its original shape (former shape) when heated at higher temperature. Let us consider a shape memory alloy for which the temperature is decreased. Due to decrease in temperature, phase transformation takes place from austenite
Characteristics of SMAs – Shape Memory Alloy Read More »
Definition : Shape memory alloys are special type of alloys that have the ability to return to a original defined shape when heated. Shape memory alloys are also called as smart materials (or) intelligent materials (or) active materials. The shape memory transformation was first observed by Chang and Read in 1932. Examples of SMA’s a)
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Since the atoms in the metallic glasses are disordered, they have some peculiar properties as follows. a) Structural properties Metallic glass have tetrahedral closely packed (TCP) structure rather than hexagonal closely packed (HCP) structure. They do not have any crystal defects such as grain boundaries, dislocations, etc. b) Mechanical (or) General properties The metallic glasses
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1. Calculate the intrinsic carrier concentration in germanium at 300 K. Given that me *=1.09 m0, mh *=0.31 m0 and Eg = 0.68 eV. Given T = 300 K, k=1.38×10-23 Jk-1, h=6.626×10-34 Js, m0 = 9.11×10-31 Kg, Eg = 0.68 eV = 0.68×1.6×10-19 J, me *=1.09 m0 = 9.929×10-31 Kg, mp* = 0.31 m0 =
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1. A uniform silver wire has a resistivity of 1.54 × 10-8 Ωm at room temperature, for an electrical field along the wire of 1 V/cm. Compute the drift velocity of electron assuming the there are 5.8 × 1028 Conducting electrons/m³. Also calculate the mobility. Given ρ = 1.54 × 10-8 Ωm, E = 1
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1. If an ionic crystal is subjected to an electric field of 1000 V/m and the resulting polarization is 4.3 × 10-8 cm², Calculate the relative permittivity of the crystal. Given E = 1000 V/m, ε0 =8.85×10-12 F/m, P = 4.3 × 10-8 C/m², εr = ? Solution :- [latex] \begin{aligned} P & =\varepsilon_{\mathrm{o}}\left(\varepsilon_{\mathrm{r}}-1\right) \mathrm{E} \\
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Ferro-electricity When a dielectric material exhibits electric polarization even in the absence of external field, it is known as ferro-electricity and these materials are termed as ferro-electrics. Ferro-electric Ferro-electrics are anisotropic crystals which exhibit spontaneous polarization, i.e., they exhibit polarization even in the absence of external electric field. Examples (i) Rochelle salt. (ii) Barium titanate
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If N be the number of molecules per unit volume and α the molecular polarizability then Total polarization [latex] \quad \mathrm{P}=\mathrm{N} \alpha \mathrm{E}_{\mathrm{int}} [/latex] eqn, (10) [latex] \therefore \quad E_{\text {int }}=\frac{\mathrm{P}}{\mathrm{N} \alpha} [/latex] Further, we know that [latex] \begin{aligned} \mathrm{D} & =\varepsilon \mathrm{E}=\varepsilon_{0} \mathrm{E}+\mathrm{P} \\ \left(\varepsilon-\varepsilon_{0}\right) \mathrm{E} & =\mathrm{P} \\ \mathrm{E} & =\frac{\mathrm{P}}{\varepsilon-\varepsilon_{0}} \end{aligned} [/latex]
Clausius – Mossotti Equation Read More »
When a dielectric material is placed in an external electric field, it exerts a dipole moment in it. The total electric field at the atom site of the dielectric kept in an applied electric field is called the internal field. It is given by the sum of the applied field (E) and the electric fields
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When a dielectric material is subjected to an alternating field, the polarisation varies with time. The polarization p(t) as a function of time t is given by P(t) = P[1- exp (-t/tr)] where, P is the maximum polarization attained on prolonged application of a static field and tr is the relaxation time for the particular
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