Mock Test

Conductivity

by Anish
Updated On:

Conductivity

Total Questions: 26

11. The highest temperature attained by a superconductor is: [U.P. Lower Sub. (Pre) 2013]

Correct Answer: (e) none of the above
Solution:When superconductivity was discovered in 1911, it was found only at temperatures close to absolute zero (-273.15°C). But since then, researchers have steadily uncovered materials that superconduct at higher temperatures.

In recent years, scientists have accelerated that progress by focusing on hydrogen-rich materials at high pressure. In 2019 it was discovered that lanthanum hydride (LaH) becomes a superconductor at around 250-260 K under a pressure of 170 gigapascals.

In 2020, a near room-temperature superconductor (around 15°C or 288 K) made from hydrogen, carbon and sulphur under pressures of around 270 gigapascals was described in a paper in research magazine Nature. This is currently the highest temperature at which any material has shown superconductivity.

12. The newly discovered high temperature superconductors are - [Uttarakhand P.C.S. (Pre) 2006 U.P.P.C.S. (Pre) 2000]

Correct Answer: (c) Ceramic oxides
Solution:Ceramic oxides play a vital role in the field of research and discovery towards superconductivity. Ceramic super conductive materials contain Mercury (Hg)/Thallium (Tl), Barium (Ba), Calcium (Ca) and Copper oxide (CO). Its discovery was first reported in 1993 and its transition temperature (T) was between 94K -135K.

13. At which temperature superconductivity can be of tremendous economic interest saving billions of rupees? [U.P.P.C.S. (Pre) 2000]

Correct Answer: (c) at room temperature.
Solution:If we could achieve superconductivity at room temperature then we can save billions of rupee through electric transmission without any power loss.

14. The conductivity of a semiconductor at zero Kelvin is [RAS/R.T.S. (Pre) 1999-2000]

Correct Answer: (d) zero
Solution:The materials (Germanium, Silicon) whose electrical conductivity varies between conductors and dielectric are called semiconductors. At absolute zero temperature, a semiconductor behaves like a perfect dielectric or insulator.

15. The resistance of a semiconductor on heating: [U.P.P.C.S.(MAINS) 2015]

Correct Answer: (b) Decreases
Solution:With the increase in temperature, the conductivity of the semiconductor material increases. As with increase in temperature, outermost electrons acquire energy and hence by acquiring energy, the outermost electrons leave the shell of the atom.

Hence, with an increase in temperature, number of carriers in the semiconductor material increases. Which leads to increase in the conductivity of the material. So we can say that the semiconductor material has negative temperature coefficient i.e. with an increase in temperature resistance decreases.

16. On heating, the resistance of a semiconductor: [66 B.P.S.C. (Pre) 2020]

Correct Answer: (b) decreases
Solution:With the increase in temperature, the conductivity of the semiconductor material increases. As with increase in temperature, outermost electrons acquire energy and hence by acquiring energy, the outermost electrons leave the shell of the atom.

Hence, with an increase in temperature, number of carriers in the semiconductor material increases. Which leads to increase in the conductivity of the material. So we can say that the semiconductor material has negative temperature coefficient i.e. with an increase in temperature resistance decreases.

17. Electric conduction in a semiconductor takes place due to- [Uttarakhand P.C.S. (Pre) 2016]

Correct Answer: (c) Both electrons and holes.
Solution:When electric field is applied across a semiconductor, the current conduction takes place by free electrons and holes. The free electrons are produced due to the breaking up of some covalent bonds by thermal energy. At the same times holes are created in the covalent bonds. Under the influence of electric field, conduction takes place by these free electrons and holes.

18. Which of the following technique cannot be used for generating electron-hole pairs in electronic devices? [M.P.P.C.S.(PRE) 2022]

Correct Answer: (d) Impurity injection
Solution:Generation of electron-hole pairs in semiconductors in electronic devices can be achieved by thermal excitation (by increasing temperature), impact ionization (by which one energetic charge carrier can loose energy by the creation of other charge carriers) or photo excitation (by utilizing the photoelectric effect).

Impurity injection is done for doping of semiconductors for the purpose of modulating its electrical, optical and structural properties. This process doesn't generate electron-hole pairs.

19. At absolute zero temperature, the electric resistance in semiconductor is- [R.A.S/R.T.S. (Pre) 1992]

Correct Answer: (a) Infinite
Solution:The electrical conductivity of a semiconductor at absolute zero temperature is zero and they behave like an insulator. At this temperature their electric resistivity becomes infinite.

20. Which one of the following metals is used as semiconductor in transistors? [44th B.P.S.C. (Pre) 2000]

Correct Answer: (b) Germanium
Solution:Germanium and silicon are the main elements which are used as a semiconductor in transistors. Their conductivity on the normal/room temperature lies between the conductivity of conductors and insulators.

Anish

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