Which one of the following statements about the refractive index of a material medium with respect to air is correct?
- A.It can be either positive or negative
- B.It can have zero value
- C.It is unity for all materials
- D.It is always greater than one
Correct answer
Explanation
The correct answer is D, It is always greater than one. Light travels fastest in vacuum and almost as fast in air, so in any material medium it moves more slowly than in air, and the ratio of the two speeds is greater than one. The refractive index of a medium with respect to air is the speed of light in air divided by the speed of light in that medium. Because the speed in a material is always lower, the index is always more than one. Typical values are about 1.33 for water, 1.5 for ordinary glass and 2.42 for diamond, which bends light the most and so sparkles. Option A is wrong because a ratio of two speeds of ordinary materials is positive; negative values belong only to specially engineered metamaterials, not ordinary media. Option B is wrong because a zero index would mean infinite speed, which is impossible. Option C is wrong because an index of one would mean the medium slows light no more than air does, which is true only of air itself. Exam tip: n = c/v; the higher n, the denser the medium optically.
Practice Questions
View allThe fact that the planets move around the Sun, not in circles but in ellipses, was first demonstrated by
- A.Galileo
- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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In 1609 Kepler showed that the planets move around the Sun in elliptical orbits, with the Sun at one focus of the ellipse.
Read the full explanation →Which one of the following statements is correct?
- A.Urea is produced in liver.
- B.Urea is produced in blood.
- C.Urea is produced from digestion of starch.
- D.Urea is produced in lung and kidney.
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Liver cells turn the toxic ammonia released from the breakdown of amino acids into urea through the ornithine cycle, also called the urea cycle.
Read the full explanation →Which one of the following is the correct sequence of passage of light in a compound microscope?
- A.Condenser-Objective lens-Eyepiece-Body tube
- B.Objective lens-Condenser-Body tube-Eyepiece
- C.Condenser-Objective lens-Body tube-Eyepiece
- D.Eyepiece-Objective lens-Body tube-Mirror
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Light passes through the condenser to the specimen, is picked up by the objective lens, travels up the body tube and reaches the eye through the eyepiece.
Read the full explanation →Which one of the following statements regarding haemoglobin is correct?
- A.Haemoglobin present in RBC can carry only oxygen but not carbon dioxide.
- B.Haemoglobin of RBC can carry both oxygen and carbon dioxide.
- C.Haemoglobin of RBC can carry only carbon dioxide.
- D.Haemoglobin is only used for blood clotting and not for carrying gases.
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It binds oxygen at its iron-containing haem groups and carries some carbon dioxide on its protein chains. Each haemoglobin molecule has four polypeptide chains and four haem groups, and each haem iron can hold one oxygen molecule, forming oxyhaemoglobin in the lungs.
Read the full explanation →Which one of the following statements regarding histone proteins is correct?
- A.Histones are proteins that are present in mitochondrial membrane.
- B.Histones are proteins that are present in nucleus in association with DNA.
- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
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They are the proteins around which DNA winds to form chromatin in the nucleus of eukaryotic cells. Histones are small basic proteins, rich in the positively charged amino acids lysine and arginine, which attract the negatively charged phosphate groups of DNA.
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