Explanation
According to Wien’s displacement law.
Since the curved surface of the conductor is thermally insulated, therefore, in steady state, the rate of flow of heat at every section will be the same. Hence the curve between H and x will be straight line parallel to x-axis.
In steady state the temperature decreases exponentially from heat end to cold end. Also the temperature decreases more rapidly near hot end and goes down to slow towards cold end.
Energy incident is to be absorbed, so choices (a) and (b) are correct. As temperature increases, energy emitted in the form of visible light, so choice (c) is correct. Reflection depends on the nature of surface which is independent of temperature, so choice (d) is correct.
During the day when water is cooler than the land, the wind blows off the water onto the land (as warm air rises and cooler air fills the place). Also at night, the effect is reversed (since the water is usually warmer than the surrounding air on land). Due to this wind flow the temperature near the sea coast remains moderate.
Heat is carried away from a fire sideways mainly by radiations. Above the fire, heat is carried by both radiation and by convection of air. The latter process carries much more heat.
Woolen fibres enclose a large amount of air in them. Both wool and air are the bad conductors of heat and the coefficient of thermal conductivity is small. So, they prevent any loss of heat from our body.
Hollow metallic closed container maintained at a uniform temperature can act as source of black body. It is also well-known that all metals cannot act as black body because if we take a highly metallic polished surface. It will not behave as a perfect black body.
We know that to measure thermal conductivity of liquids experimentally, they must be heated from the top i.e., upper layer is kept hot and lower layer is kept cold, so as to prevent convection in liquids.
The thermal conductivity of brass is high i.e., brass is a good conductor of heat. So, when a brass tumbler is touched, hear quickly flows from human body to tumbler. Consequently, the tumbler appears colder, on the other hand wood is a bad conductor. So, heat does not flow from the human body to the wooden tray in this case. Thus it appears comparatively hotter.
Light radiations and thermal radiations both belong to electromagnetic spectrum. Light radiations belong to visible region while thermal radiation belong to infrared region of EM spectrum. Also, EM radiations requires no medium for propagation.
When the temperature of the atmosphere reaches below OC, then the water vapours present in air, instead of condensing, freeze directly in the form of minute particles of ice. Many particles coalesce and take cotton-like shape which is called snow. Thus snow contains air packets in which convection currents cannot be formed. Hence snow is a good heat insulator. In ice there is no air, so it is a bad insulator.
When water leaves the body through perspiration energy content of molecules remained in body decreases, therefore temperature also decreases.
Both Assertion and Reason are true but Reason is not’correctly explaining the Assertion.
The 98.4°F is the standard body temperature of a man. If a man touches an iron or wooden ball at 98.4°F, no heat transfer takes place between ball and man, so both the halls would feel equally hot for the man.
It is not necessary that all black coloured objects are black bodies. For example, if we take a black surface which is highly polished, it will not behave as a perfect black body.
A perfectly black body absorbs all the radiations incident on it.
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