## Saturday, June 29, 2019

### Question from Material Science (Summer 2019) AMIE Exam

At room temperature, the electrical conductivity of PbS is 25 (Ω.m)-1, whereas the electron and hole mobilities are 0.06 and 0.02 m2/V.s, respectively. Calculate the intrinsic carrier concentration for PbS at room temperature. (AMIE, Material Science, Summer 2019)

Solution
$\begin{array}{l}\sigma = 25{(\Omega m)^{ - 1}}\\{\mu _e} = 0.06{m^2}/Vs\\{\mu _h} = 0.02{m^2}/Vs\end{array}$
In the intrinsic region
$n = p = {n_i}$
So, $\sigma = {n_i}\left| e \right|({\mu _e} + {\mu _h})$
$\therefore {n_i} = \frac{\sigma }{{\left| e \right|({\mu _e} + {\mu _h})}} = \frac{{25}}{{1.6x{{10}^{ - 19}}(0.06 + 0.02)}} = 1.95x{10^{21}}{m^{ - 3}}$

Study material for AMIE Exams

## Friday, June 28, 2019

### A numerical from Material Science (Summer 2019 AMIE Question paper)

Find the equilibrium concentration of vacancies in aluminium at 300 K and 900 K. Given ΔH= 68 kJ/mol (AMIE, Material Science, Summer 2019, 10 marks)

Solution

At 300 K
$\frac{{{N_v}}}{N} = \exp \left( {\frac{{68x{{10}^3}\Delta {H_f}}}{{8.314x300}}} \right) = \exp ( - 27.26) = 1.45\,x\,{10^{ - 12}}$

## Thursday, June 27, 2019

### Short Answer Questions from "Design & Manufacturing" (Summer 2019 AMIE Exams)

What is Organizational need?
An organizational needs analysis helps you to compare the current skills in your company with the skills you need to meet future business objectives. If, for example, you want to move into a market that demands high levels of after-sales service, you must ensure that you have people with the skills to deliver service.

What is concurrent engineering?
Concurrent engineering, also known as simultaneous engineering, is a method of designing and developing products, in which the different stages run simultaneously, rather than consecutively. It decreases product development time and also the time to market, leading to improved productivity and reduced costs.

For what Carbon dioxide casting is used for?
This process is used for the production of large moulds from wooden patterns, and for small repetition castings to a high standard of surface finish and close dimensional tolerance thus acting as a substitute for shell moulding.

What is the effect of temperature in metal forming?
There are three basic temperature ranges at which the metal can be formed, cold working, warm working, and hot working.

• Cold working, (or cold forming), is a metal forming process that is carried out at room temperature or a little above it. In cold working, plastic deformation of the work causes strain hardening.
• Warm working, (or warm forming), is a metal forming process carried out above the temperature range of cold working, but below the recrystallization temperature of the metal.
• Hot working, (or hot forming), is a metal forming process that is carried out at a temperature range that is higher than the recrystallization temperature of the metal being formed. When above its recrystallization temperature a metal has a reduced yield strength, also no strain hardening will occur as the material is plastically deformed. Shaping a metal at the hot working temperature range requires much less force and power than in cold working. Above its recrystallization temperature, a metal also possesses far greater ductility than at its cold worked temperature.

Define oblique cutting.
In oblique cutting,  the cutting edge of wedge shape-cutting tool makes an angle except for right angle to the direction of tool motion. In oblique cutting, chip flow deviates from the orthogonal plane. The tool is presented to the workpiece at an acute angle (θ < 90°) to the tool feed motion.

Honing is used for?
Honing is an abrasive machining process that produces a precision surface on a metal workpiece by scrubbing an abrasive stone against it along a controlled path. Honing is primarily used to improve the geometric form of a surface, but may also improve the surface texture.

Carburizing flame is used for welding which type of materials?
A carburizing flame is advantageous for welding high carbon steel and hard facing such nonferrous alloys as nickel and Monel.

Define AS & RS.
An automated storage and retrieval system (ASRS or AS/RS) consists of a variety of computer-controlled systems for automatically placing and retrieving loads from defined storage locations.

The function of dielectric in EDM.
EDM dielectric fluid serves two main purposes. First, it acts as a semiconductor between the electrode and workpiece to facilitate a stable and controlled spark gap ionization condition. Second, it also acts as a flushing agent to wash and remove the eroded debris from the spark gap area.

Define Robust design
Robust product design is a concept from the teachings of Dr Genichi Taguchi, a Japanese quality guru. It is defined as reducing variation in a product without eliminating the causes of the variation (environmental variation during the product’s usage, manufacturing variation, and component deterioration). In other words, making the product or process insensitive to variation.

Study material for AMIE exams