Twinkling of a star is due to :
- A.Interference of light
- B.Refraction of light
- C.Polarization of light
- D.Diffraction of light
Correct answer
Explanation
The correct answer is B, Refraction of light. Starlight is bent again and again by layers of air of changing density, so its path and brightness keep shifting and the star seems to twinkle.
The Earth's atmosphere is not uniform: its temperature and density change from layer to layer and from moment to moment. Light from a star bends each time it enters a layer with a different refractive index. Because a star is so far away that it acts as a point source, these small shifts change the amount of light reaching the eye, and it flickers. Planets are much closer and look like small discs, so the changes average out and planets do not twinkle.
A is wrong: interference is the overlap of two coherent waves, as in soap films, not the cause of twinkling.
C is wrong: polarisation is about the direction of vibration of light and has nothing to do with twinkling.
D is wrong: diffraction is bending around small obstacles or slits, not bending in the air.
Exam tip: twinkling of stars, the advance sunrise and delayed sunset, and the apparent flattening of the Sun all come from atmospheric refraction.
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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