Which one of the following is not a semiconductor?
- A.Silicon
- B.Germanium
- C.Quartz
- D.Gallium arsenide
Correct answer
Explanation
The correct answer is C, Quartz. Quartz is crystalline silicon dioxide (SiO₂), an electrical insulator, not a semiconductor.
A semiconductor has a conductivity between that of a conductor and an insulator, and its conductivity rises with temperature or when impurities are added (doping). In quartz the gap between the valence and conduction bands is very wide, so almost no electrons can carry current. Quartz is, however, piezoelectric: it produces a voltage when pressed and vibrates at a steady frequency in an electric field, which is why quartz crystals keep time in watches and clocks.
A is wrong: silicon is the most widely used semiconductor, the base of computer chips and solar cells.
B is wrong: germanium is an elemental semiconductor that was used in the first transistors.
D is wrong: gallium arsenide is a compound semiconductor used in LEDs, lasers and high-speed electronics.
Exam tip: elemental semiconductors = Si, Ge; compound = GaAs, CdS; quartz (SiO₂) = insulator and piezoelectric, used in watches.
Practice Questions
View allWhich one of the following cell organelles contains DNA?
- A.Golgi apparatus
- B.Mitochondrion
- C.Lysosome
- D.Endoplasmic reticulum
Show answer
Mitochondria carry their own small, circular DNA and their own ribosomes. Mitochondria are the powerhouses of the cell, where aerobic respiration makes ATP.
Read the full explanation →Which set of vegetables is underground stem or modified stem of a plant?
- A.Potato, artichoke, round gourd
- B.Onion, garlic, carrot
- C.Potato, onion, garlic
- D.Potato, garlic, turnip
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All three are underground modified stems: the potato is a stem tuber, and onion and garlic are bulbs. A stem can be told from a root by its nodes and buds.
Read the full explanation →A sound wave having frequency of 300 Hz is travelling in an unknown medium. Its wavelength is not known. It travels a distance equal to 150 times its wavelength in time t. The value of t is :
- A.0.5 s
- B.1 s
- C.1.5 s
- D.2 s
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A wave moves forward by one wavelength in each cycle, so 150 wavelengths take 150 cycles, and 150 cycles at 300 per second take half a second.
Read the full explanation →A body floats in a liquid if the buoyant force is :
- A.equal to its weight.
- B.less than its weight.
- C.greater than its weight.
- D.zero.
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A floating body is in equilibrium, so the upward buoyant force exactly balances its weight. By Archimedes' principle, a body in a liquid is pushed up by a force equal to the weight of the liquid it displaces.
Read the full explanation →Which of the following are the different parts of a human brain ?
- A.Forefront brain, Standard brain and Hind brain
- B.Fore brain, Median brain and Rear brain
- C.Fore brain, Mid brain and Hind brain
- D.Precursor brain, Mean brain and Hind brain
Show answer
These are the three main divisions of the human brain. The fore brain is the largest part.
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