Which one of the following heat transfers is an example of convection ?
- A.Heating of food in a microwave oven
- B.Boiling water in a pot on a gas stove
- C.Feeling the warmth in sun
- D.Heating a brass rod at one end and observing the temperature rise at the other end
Correct answer
Explanation
The correct answer is B, Boiling water in a pot on a gas stove. The water at the bottom warms, becomes lighter and rises, while cooler water sinks to take its place, and these convection currents carry heat through the pot.
Convection is the transfer of heat by the actual movement of a fluid, a liquid or a gas. It needs gravity and a difference in density between warm and cool parts. Sea breezes, land breezes, the circulation of air in a room heater and the rising of hot air in the atmosphere are all convection. Conduction, by contrast, passes heat from particle to particle in a solid without the material moving, and radiation carries heat as electromagnetic waves, even through a vacuum.
Option A is wrong because a microwave oven heats food by microwaves, a form of radiation that makes water molecules vibrate. Option C is wrong because the Sun's warmth reaches us by radiation across empty space. Option D is wrong because heat travels along a brass rod by conduction.
Exam tip: conduction in solids, convection in liquids and gases, radiation through vacuum.
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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