Thermal Propert...

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Assertion : A body that is a good radiator is also a good absorber of radiation at a given wavelength.

Reason : According to Kirchhoff's law the absorptivity of a body is equal to its emissivity at a given wavelength.

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Assertion : Temperatures near the sea coast are moderate.

Reason : Water has a high thermal conductivity.

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Assertion : Bodies radiate heat at all temperatures.

Reason : Rate of radiation of heat is proportional to the fourth power of absolute temperature.

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Assertion : The equivalent thermal conductivity of two plates of same thickness in contact (series) is less than the smaller value of thermal conductivity.

Reason : For two plates of equal thickness in contact (series) the equivalent thermal conductivity is given by

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Assertion : If the temperature of a star is doubled then the rate of loss of heat from it becomes 16 times.

Reason : Specific heat varies with temperature.

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Assertion : Blue star is at high temperature than red star.

Reason : Wein's displacement law states that T∝(1/λ_m).

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Assertion : A brass tumbler feels much colder than a wooden tray on a chilly day.

Reason : The thermal conductivity of brass is less than that of wood.

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Assertion : For higher temperature, the peak emission wavelength of a black body shifts to lower wavelengths.

Reason : Peak emission wavelength of a blackbody is proportional to the fourth power of temperature.

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Assertion : It is hotter over the top of a fire than at the same distance on the sides.

Reason : Air surrounding the fire conducts more heat upwards.

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Assertion : Woolen clothes keep the body warm in winter.

Reason : Air is a bad conductor of heat.