Electrical Engineering Materials — Part 1 MCQs with Explanations

The resistivity $$ \rho $$ of a material depends on multiple factors, and all of the mentioned options contribute to it: Resistance of the conductor: The resistivity is directly related to the resistance through the formula $$ R = \rho \frac{L}{A} $$, where $$ R $$ is the resistance, $$ \rho $$ is the resistivity, $$ L $$) is the length of the conductor, and $$ A $$ is the area of the conductor section. Area of the conductor section: The area of the conductor section $$( A )$$ is present in the denominator of the resistance formula. As the area increases, the resistance decreases, and vice versa. Length of the conductor: The length of the conductor $$( L )$$ is also present in the numerator of the resistance formula. As the length increases, the resistance increases, and vice versa. Therefore, the correct answer is Option D: All of the above .

Selenium is an intrinsic semiconductor. An intrinsic semiconductor is one that is pure and contains no significant dopants or impurities. In the case of selenium, it is an intrinsic semiconductor when it is in its pure form. Intrinsic semiconductors have equal numbers of electrons and holes, allowing for the flow of current under certain conditions. Extrinsic semiconductors, on the other hand, are those that have been intentionally doped with impurities to alter their electrical properties. These can be further categorized into N-type and P-type semiconductors based on the type of doping introduced. Therefore, the correct spelling of the term is intrinsic , making Option B the correct

H.R.C. stands for High Rupturing Capacity. This means the fuse can safely interrupt very high fault currents. Fuses are designed to protect electrical circuits from overcurrents. Option A is correct: H.R.C. fuses typically have a ceramic body for insulation and heat resistance, and metal end caps to connect it to the circuit. Option B is incorrect: Platinum is expensive and not typically used in fuses. Option C is incorrect: A heavy cross-section of copper or aluminum would carry a lot of current without blowing, defeating the purpose of a fuse. Fuses need a specifically designed element that melts. Option D is incorrect: Carbon rods are generally used in resistance applications, not as fuse elements in H.R.C. fuses. Also, carbon has a relatively high resistance, unlike fuse elements that need a very low resistance.

In a simple cubic structure, each particle or atom is in contact with six nearest neighbors. This arrangement leads to a coordination number of 6 for a simple cubic lattice. Therefore, the correct answer is Option D: 6 .

Superconductors are materials that exhibit zero electrical resistance and expel magnetic fields below a certain critical temperature. Strong magnetic fields are generated in applications like MRI machines, particle accelerators, and fusion reactors by using superconducting coils. These coils can carry extremely high currents without any energy loss due to their superconducting properties, enabling the generation of very strong magnetic fields. Other options like generating electrostatic fields or regions free from magnetic fields are not related to the primary applications of superconductors. Therefore, Option A is the correct answer.

Temperature coefficient of resistance (TCR) indicates how much the resistance of a material changes with temperature. A material with a low temperature coefficient shows very little change in resistance when temperature varies, which is desirable for precision resistors and measuring instruments. Constantan has an extremely low and nearly zero temperature coefficient of resistance compared to other resistive materials listed. Nichrome and Kanthal have higher temperature coefficients and are mainly used for heating elements where resistance change is acceptable. Molybdenum is a metal with a relatively high positive temperature coefficient of resistance. Therefore, the resistive material with the lowest temperature coefficient of resistance is Constantan .

The conductivity of an extrinsic semiconductor (doped semiconductor) changes with temperature. It is influenced by the number of charge carriers (either electrons or holes) and their mobility within the material. The behavior of conductivity with temperature depends on the type of extrinsic semiconductor: In an n-type extrinsic semiconductor (where the majority charge carriers are electrons), as the temperature increases, more electrons are promoted from the valence band to the conduction band, resulting in increased electron concentration. This leads to an increase in conductivity with temperature. In a p-type extrinsic semiconductor (where the majority charge carriers are holes), as the temperature increases, more holes are generated in the valence band, contributing to an increase in hole concentration. This also results in an increase in conductivity with temperature. So, for both n-type and p-type extrinsic semiconductors, the conductivity increases with temperature.

Ultrasonic waves is the correct answer to “Piezoelectric materials serve as a source of ________ .”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

Unit cell is the correct answer to “The tiny block formed by the arrangement of a small group of atoms is called the”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

2 is the correct answer to “The number of atoms per unit cell in B.C.C. structure is”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

Pure annealed copper is the correct answer to “Which of the following variety of copper has the best conductivity”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

Less than that of unbounded electron is the correct answer to “The kinetic energy of a bounded electron is”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

Application of magnetic field is the correct answer to “Super conductivity can be destroyed by”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

Decreasing its temperature is the correct answer to “The conductivity of a conductor can be increased by”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

A metal liquid is the correct answer to “Mercury as an electric contact material is”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

Cast iron is the correct answer to “________ has the best damping properties.”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

Electric field is the correct answer to “The conductors have transport phenomena of electrons due to”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

Electron is the correct answer to “Is a negatively charged particle present in an atom.”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

The amplitude of vibration of the atoms varies with temperature is the correct answer to “The resistivity of a metal is a function of temperature because”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

Copper-zinc is the correct answer to “_______ is a hard solder.”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

Critical current density is the correct answer to “The structure sensitive property of a super conductor is”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

Porcelain is the correct answer to “Spark plug makes use of which of the following materials for insulation”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

Manganin is the correct answer to “Which of the following materials is used for making coils of standard resistances”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

Temperature is the correct answer to “The minority carrier concentration is largely a function of”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

All of the above is the correct answer to “High resistivity materials are used in”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

All above applications is the correct answer to “Low resistivity materials are used in”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

Cubic is the correct answer to “Most of the common metals have _________ structure.”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

Metals is the correct answer to “Which of the following materials does not have covalent bonds”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

0.7eV is the correct answer to “For germanium the forbidden energy gap is”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

Vacuum tubes is the correct answer to “Thermonic emission occurs in”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

All of the above is the correct answer to “Copper, even though costly, finds use in the windings of electrical machines because”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

Manganin is the correct answer to “_______ has zero temperature co-efficient of resistance.”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

Silicon is the correct answer to “Which of the following is a semiconductor material”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

Copper and nickel is the correct answer to “Constantan contains”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

SiO2 is the correct answer to “__________ is the main constituent of glass.”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

Both A and B is the correct answer to “In a superconductor the value of critical density depends upon”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

Electrons and holes is the correct answer to “The conduction of electricity, in semiconductors, takes place due to movement of”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

Electrons only is the correct answer to “In conductors conduction of electricity takes place due to movement of”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

All of the above is the correct answer to “A highly conductive material must have”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.

An acceptor is the correct answer to “Is an element used in semiconductors whose atoms have three valence electrons.”. This question is standard in competitive examination syllabi for Electrical Engineering Materials.