An optical illusion which occurs mainly in deserts during hot summer is based on the principle of
- A.Reflection
- B.Interference
- C.Dispersion
- D.Total internal reflection
Correct answer
Explanation
The correct answer is D, Total internal reflection. A mirage forms when light from the sky bends through hot, less dense air near the ground and is finally totally internally reflected.
On a hot day the air close to the sand is much hotter, and so optically rarer, than the air above. Light from a distant tree or the sky travelling downward passes from denser to rarer layers, bending away from the normal each time. When it meets a layer at an angle greater than the critical angle, it is reflected upward into the observer's eye. The eye sees an inverted image below the object, which looks like a pool of water. The same effect makes hot roads look wet.
A is wrong: ordinary reflection needs a reflecting surface; there is no water or mirror on the sand.
B is wrong: interference produces bright and dark bands, as in thin oil films, not mirages.
C is wrong: dispersion splits white light into colours, as in a prism or rainbow.
Exam tip: mirage, sparkling diamond and optical fibre all work on total internal reflection; rainbow uses dispersion, refraction and internal reflection.
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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