The 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
Correct answer
Explanation
The correct answer is C, Johannes Kepler. In 1609 Kepler showed that the planets move around the Sun in elliptical orbits, with the Sun at one focus of the ellipse.
Working with the precise observations of the Danish astronomer Tycho Brahe, Kepler studied the orbit of Mars and found that no circle fitted it. His first law says that orbits are ellipses. His second law says that the line joining a planet to the Sun sweeps out equal areas in equal times, so a planet moves faster when it is nearer the Sun. His third law, of 1619, links the square of a planet's period to the cube of its average distance. Newton later explained all three with his law of gravitation.
Option A is wrong because Galileo supported the Sun-centred model with his telescope but still believed in circular orbits. Option B is wrong because Martin Luther was a religious reformer, not an astronomer. Option D is wrong because Copernicus placed the Sun at the centre in 1543 but kept circular orbits.
Exam tip: Copernicus = Sun at the centre (1543); Kepler = elliptical orbits (1609); Newton = gravitation (1687).
Practice Questions
View allWhich 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.
Read the full explanation →The Hooke's law is valid for
- A.only proportional region of the stress-strain curve
- B.entire stress-strain curve
- C.entire elastic region of the stress-strain curve
- D.elastic as well as plastic region of the stress-strain curve
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Hooke's law says stress is directly proportional to strain, and that holds only up to the proportional limit, where the curve is a straight line.
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