Which one of the following is not a property of 'graphene'?
- A.It is the thinnest material known so far.
- B.It is almost completely transparent.
- C.It is highly conducting.
- D.It is a wide band-gap semiconductor.
Correct answer
Explanation
The correct answer is D. Graphene is not a wide band-gap semiconductor; it has practically zero band gap and behaves like a semimetal.
Graphene is a single layer of carbon atoms arranged in a honeycomb lattice, first isolated from graphite in 2004 by Andre Geim and Konstantin Novoselov, who received the Nobel Prize in Physics in 2010. Being one atom thick, it is the thinnest material known. A single sheet absorbs only about 2.3% of visible light, so it is nearly transparent. Its electrons move very fast, which makes it an excellent conductor of electricity and heat, and it is also extremely strong.
A is wrong as a choice: being one atom thick, graphene is indeed the thinnest material.
B is wrong as a choice: it lets through almost all visible light.
C is wrong as a choice: it conducts electricity very well.
Exam tip: graphene means one atom thick, strong, transparent, highly conducting, zero band gap; Nobel 2010 to Geim and Novoselov.
Practice Questions
View allWhich of the following properties is true for a tooth paste?
- A.It is acidic
- B.It is neutral
- C.It is basic
- D.It is made up of Calcium phosphate, the material of tooth enamel
Show answer
Toothpaste is mildly basic so that it can neutralise the acid that causes tooth decay. Bacteria in the mouth break down sugar and food particles left on the teeth and produce acids.
Read the full explanation →A stainless steel chamber contains Ar gas at a temperature T and pressure P. The total number of Ar atoms in the chamber is n. Now Ar gas in the chamber is replaced by CO₂ gas and the total number of CO₂ molecules in the chamber is n/2 at the same temperature T. The pressure in the chamber now is P'. Which one of the following relations holds true? (Both the gases behave as ideal gases)
- A.P' = P
- B.P' = 2P
- C.P' = P/2
- D.P' = P/4
Show answer
For an ideal gas in a fixed volume at a fixed temperature, pressure is proportional to the number of molecules, so half the molecules give half the pressure.
Read the full explanation →In which of the following pairs are the ions isoelectronic?
- A.Mg²⁺, Ar
- B.Na⁺, O²⁻
- C.Al³⁺, Cl⁻
- D.K⁺, Ne
Show answer
Both have 10 electrons, the same number as a neon atom, so they are isoelectronic. Isoelectronic species have the same number of electrons.
Read the full explanation →A solid disc and a solid sphere have the same mass and same radius. Which one has the higher moment of inertia about its centre of mass?
- A.The disc
- B.The sphere
- C.Both have the same moment of inertia
- D.The information provided is not sufficient to answer the question
Show answer
About an axis through the centre, a solid disc has I = ½MR² while a solid sphere has I = ⅖MR², and ½ is larger than ⅖.
Read the full explanation →Numerically two thermometers, one in Fahrenheit scale and another in Celsius scale shall read same at
- A.−40°
- B.0°
- C.−273°
- D.100°
Show answer
At this one temperature the Celsius and Fahrenheit scales show the same number. The two scales are linked by F = (9/5)C + 32.
Read the full explanation →