The phenomenon used in optical fibre for transmission of light energy is
- A.Total internal reflection
- B.Diffraction
- C.Scattering
- D.Refraction
Correct answer
Explanation
The correct answer is A, Total internal reflection. When light travels from a denser medium to a rarer one and strikes the boundary at an angle greater than the critical angle, it does not pass out at all but is reflected completely back. An optical fibre uses exactly this. It has a thin glass or plastic core of higher refractive index, covered by a cladding of lower refractive index, so light entering one end keeps bouncing off the walls and travels long distances, even around bends, with very little loss. That is why fibres carry internet and telephone signals and are used in endoscopes to see inside the body. The Indian-born physicist Narinder Singh Kapany is called the father of fibre optics. Option B is wrong because diffraction is the bending of light around small obstacles or through narrow slits. Option C is wrong because scattering spreads light in many directions, which makes the sky look blue. Option D is wrong because refraction is only the bending of light as it enters a new medium, while a fibre works by stopping light from escaping. Exam tip: optical fibre, mirage and a sparkling diamond all work by total 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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