Which one of the following waves is used for detecting forgery in currency notes ?
- A.Ultraviolet waves
- B.Infrared waves
- C.Radio waves
- D.Microwaves
Correct answer
Explanation
The correct answer is A, Ultraviolet waves. Genuine currency notes carry security features printed with fluorescent inks that glow only under ultraviolet light, so a UV lamp quickly exposes a fake. Banknote paper is also made without the optical brighteners found in ordinary paper, so under UV light a real note stays dull while many forged notes glow all over. Ultraviolet rays have shorter wavelengths than visible violet light and make certain substances fluoresce; the same property is used to check documents, passports and works of art. Option B is wrong because infrared waves are felt as heat and are used in remote controls, night-vision cameras and heating, not in the standard note check. Option C is wrong because radio waves are used for broadcasting and communication. Option D is wrong because microwaves are used in microwave ovens, radar and satellite links. Exam tip: UV = fake-note detection and sterilisation; IR = remote control and night vision.
Practice Questions
View allEqual volumes of all gases, under the same conditions of temperature and pressure, contain an equal number of molecules. This statement is known as
- A.Avogadro's law
- B.Boyle's law
- C.Charles's law
- D.Dalton's law of partial pressures
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It is the reason one mole of every gas occupies the same 22.4 litres at standard temperature and pressure, and it allowed chemists to settle the formulae of gases such as hydrogen and oxygen as having two atoms each.
Read the full explanation →Carbon forms two oxides, carbon monoxide and carbon dioxide, in which twelve grams of carbon combines with sixteen grams and thirty two grams of oxygen respectively. This illustrates
- A.The law of conservation of mass
- B.The law of constant proportions
- C.The law of multiple proportions
- D.Avogadro's law
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When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other bear a simple whole number ratio, and here the oxygen masses of sixteen and thirty two grams for the same twelve grams of carbon are in the ratio…
Read the full explanation →How many moles are present in 36 grams of water?
- A.One mole
- B.Two moles
- C.Three moles
- D.Half a mole
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The molecular mass of water is eighteen unified atomic mass units, two hydrogen atoms of 1 u each and one oxygen atom of 16 u, so one mole of water weighs eighteen grams.
Read the full explanation →One unified atomic mass unit, written as u, is defined as
- A.The mass of one hydrogen atom
- B.One twelfth of the mass of one atom of carbon twelve
- C.One sixteenth of the mass of one atom of oxygen
- D.The mass of one electron
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This standard was adopted so that the atomic masses of all elements could be compared on one relative scale, and on it hydrogen comes out as about 1 u, oxygen as 16 u and chlorine as 35.5 u. Option A is wrong because the hydrogen atom was the standard in…
Read the full explanation →At standard temperature and pressure, the volume occupied by one mole of any gas is
- A.11.2 litres
- B.22.4 litres
- C.24.4 litres
- D.1 litre
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It follows from Avogadro's law: since equal volumes of all gases at the same temperature and pressure contain an equal number of molecules, one mole of hydrogen, of oxygen or of carbon dioxide all take up the same space at standard temperature and pressure, even though their masses are two…
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