Water boils at a lower temperature at high altitudes, because
- A.the air pressure is less
- B.outside temperature is less
- C.latent heat is less
- D.None of the above
Correct answer
Explanation
The correct answer is A, the air pressure is less. A liquid boils when its vapour pressure equals the pressure of the air pressing on its surface, so lower air pressure means a lower boiling point. At sea level the atmosphere presses with about 101 kilopascals and water boils at 100 degrees Celsius. On a hill station the column of air above is shorter, the pressure falls, and water may boil at 90 degrees or less, which is why rice and pulses cook slowly in the mountains and a pressure cooker, which raises the pressure inside, is used to cook them faster. Option B is wrong because the surrounding temperature only decides how long heating takes, not the temperature at which boiling begins. Option C is wrong because the latent heat of vaporisation is a property of water and does not shrink with altitude. Option D is wrong because option A already states the correct reason. Exam tip: boiling point rises with pressure and falls with altitude; that single rule explains both the cooker and the hill station.
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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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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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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