Which of the following statements is true/correct
Medium
Download our app for free and get startedPlay store
(b) During clear nights object on surface of earth radiate out heat and temperature falls. Hence option $(a)$ is wrong.

The total energy radiated by a body per unit time per unit area $E \propto T^4$. Hence option $(c)$ is wrong.

Energy radiated per second is given by $\frac{Q}{t} = PA\varepsilon \sigma {T^4}$

==> $\frac{{{P_1}}}{{{P_2}}} = \frac{{{A_1}}}{{{A_2}}}.{\left( {\frac{{{T_1}}}{{{T_2}}}} \right)^4} = {\left( {\frac{{{r_1}}}{{{r_2}}}} \right)^2}.{\left( {\frac{{{T_1}}}{{{T_2}}}} \right)^4} = {\left( {\frac{1}{4}} \right)^2}\left( {\frac{{4000}}{{200}}} \right) = \frac{1}{1}$
 $\because P1 = P2$ , hence option $(d)$ is wrong.

Newton's law is an approximate form of Stefan's law of radiation and works well for natural convection. Hence option $(b)$ is correct.

art

Download our app
and get started for free

Experience the future of education. Simply download our apps or reach out to us for more information. Let's shape the future of learning together!No signup needed.*

Similar Questions

  • 1
    The amount of radiation emitted by a perfectly black body is proportional to
    View Solution
  • 2
    A body takes $5$ minutes to cool from $90^oC$ to $60^oC$. If the temperature of the surroundings is $20^oC$, the time taken by it to cool from $60^oC$ to $30^oC$ will be ...... $\min.$
    View Solution
  • 3
    Variation of radiant energy emitted by sun, filament of tungsten lamp and welding arc as a function of its wavelength is shown in figure. Which of the following option is the correct match
    View Solution
  • 4
    Three rods made of the same material and having same cross-sectional area but different lengths $10\,\,cm$, $\,\,20 cm$ and $30\,\,cm$ are joined as shown. The temperature of the joint is  ....... $^oC$ 
    View Solution
  • 5
    A black coloured solid sphere of radius $R$ and mass $M$ is inside a cavity with vacuum inside. The walls of the cavity are maintained at temperature $T_0$. The initial temperature of the sphere is $3T_0$. If the specific heat of the material of the sphere varies as $\alpha T^3$ per unit mass with the temperature $T$ of the sphere, where $\alpha $ is a constant, then the time taken for the sphere to cool down to temperature $2T_0$ will be ( $\sigma $ is Stefan Boltzmann constant)
    View Solution
  • 6
    Variation of radiant energy emitted by sun, filament of tungsten lamp and welding arc as a function of its wavelength is shown in figure. Which of the following option is the correct match
    View Solution
  • 7
    The wavelength of radiation emitted by a body depends upon
    View Solution
  • 8
    Which factor does not affect convection?
    View Solution
  • 9
    The ratio of the diameters of two metallic rods of the same material is $2 : 1$ and their lengths are in the ratio $1 : 4$ . If the temperature difference between their ends are equal, the rate of flow of heat in them will be in the ratio
    View Solution
  • 10
    When $p$ calories of heat is given to a body, it absorbs $q$ calories; then the absorbtion power of body will be
    View Solution