by a body depend on?
(b
Wildl happens to radiant heat when it falls on a body? What u
b) 4. (a) Mention one difference between the transfer of heat by conduction and that by radiation.
pat by conduction and that by convection.
Answers
Answer:
Page No 60:
Question 1:
What determines the direction of flow of heat between two objects in contact?
ANSWER:
The difference in temperature of the bodies determines the direction of flow of heat. Heat flows from a body at higher temperature to one at a lower temperature.
Page No 60:
Question 2:
In a solid being heated at one end, by which mode does heat travel from the hot end to the cold end?
ANSWER:
Heat travels via process of conduction from the hot end to the cold.
Page No 60:
Question 3:
Name two good conductors and two insulators of heat.
ANSWER:
Iron and copper are the two good conductors of heat. Whereas wood and plastic are the two insulators of heat.
Page No 60:
Question 4:
Are most liquids good or bad conductors of heat?
ANSWER:
Most liquids are bad conductors of heat.
Page No 62:
Question 1:
In the process of convection, how is heat carried from the hot to the cold part?
ANSWER:
In the process of convection, heated molecules of a liquid or gas move themselves to carry heat from the hot to the cold region.
Page No 62:
Question 2:
Why are convection currents seen in liquids and gases, and not in solids?
ANSWER:
In solid molecules are tightly bound with each other, they can vibrate but can not move to carry heat from one region to another region. That's why convection currents are seen in liquids and gases but not in solids.
Page No 62:
Question 3:
Name one natural phenomenon that occurs due to convection currents in air.
ANSWER:
Sea and land breezes in coastal areas are actually convection currents. The flow of breeze from the sea to the land or from the land to the see occurs due to the process of convection.
Page No 64:
Question 1:
Which of these does not require a medium–conduction, convection or radiation?
ANSWER:
Radiation does not require any medium. Through the process of radiation, the heat can be transferred even in the vacuum.
Page No 64:
Question 2:
Which is the fastest method of heat transfer–conduction, convection or radiation?
ANSWER:
In radiation, heat is transferred by electromagnetic waves traveling at the speed of light. Hence, radiation is the fastest method of heat transfer.
Page No 64:
Question 3:
Which of these are better absorbers of radiant heat–dark-coloured or light-coloured objects?
ANSWER:
Dark-coloured objects absorb and radiate more heat than light-coloured objects.
Page No 64:
Question 4:
Which of these are better radiators of radiant heat–dark-coloured or light-coloured objects?
ANSWER:
Dark coloured objects are better absorber and better radiator than light-coloured objects.
Page No 64:
Question 5:
Name a device that prevents loss (or gain) of energy by conduction, convection and radiation.
ANSWER:
A thermos flask is a household device which does not allow heat to flow in or out of its system. Hence, it prevents loss of energy by conduction, convection or radiation.
Page No 66:
Question 1:
Conduction takes place in
(a) solid only
(b) liquids only
(c) gases only
(d) in solids, liquids and gases
ANSWER:
(a) solid only
In conduction, the molecules vibrate and hit each other to transfer the heat energy between them. The molecules need not to travel from one end to other. Therefore, it is only possible in solids in which the molecules do not move but vibrate on heating.
Page No 66:
Question 2:
In which method of transfer of heat do the molecules travel from the hot the cold protion?
(a) conduction
(b) convection
(c) radiation
(d) all of the above
ANSWER:
(b) Convection
In the convection method, molecules travel from the hotter region to the colder region. The case is the same when water is heated.
Explanation:
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