Answer
64.8k+ views
Hint: To solve this question, we need to use the Stefan’s law to find the absolute temperature in terms of the wavelength for the two objects. Then these have to be substituted in the Wien’s displacement formula for the radiant power from where the required ratio can be calculated.
Formula used: The formulae used in solving this question are given by
${\lambda _{\max }} = \dfrac{b}{T}$, here ${\lambda _{\max }}$ is the maximum wavelength at the absolute temperature $T$, and $b$ is a constant.
\[{P_R} = \sigma {T^4}\], here \[{P_R}\] is the radiant power at the absolute temperature $T$, and $\sigma $ is the Stefan-Boltzmann constant.
Complete step-by-step solution:
Let the power emitted by the source ${O_1}$ be ${P_1}$ and that emitted by the source ${O_2}$ be ${P_2}$.
We know from the Stefan’s law that the radiant power is proportional to the fourth power of the absolute temperature. So it is given by
\[{P_R} = \sigma {T^4}\]
If the temperature of the source ${O_1}$ is equal to ${T_1}$, then the radiant power emitted by it is given by
${P_1} = \sigma {T_1}^4$........... (1)
Also, if the temperature of the source ${O_2}$ is equal to ${T_2}$, then the radiant power emitted by it is given by
${P_2} = \sigma {T_2}^4$...............(2)
Dividing (2) by (1) we get
$\dfrac{{{P_2}}}{{{P_1}}} = \dfrac{{\sigma {T_2}^4}}{{\sigma {T_1}^4}}$
\[ \Rightarrow \dfrac{{{P_2}}}{{{P_1}}} = {\left( {\dfrac{{{T_2}}}{{{T_1}}}} \right)^4}\]........(3)
Now, from the Wien’s displacement law we know that the maximum wavelength of the radiation emitted by an object is inversely proportional to its absolute temperature. So it is given by
${\lambda _{\max }} = \dfrac{b}{T}$
$ \Rightarrow T = \dfrac{b}{{{\lambda _{\max }}}}$
If ${\lambda _1}$ is the maximum temperature of the object ${O_1}$ then its absolute temperature is
${T_1} = \dfrac{b}{{{\lambda _1}}}$.........(4)
Also, if the maximum temperature of the object ${O_1}$ then its absolute temperature is
${T_2} = \dfrac{b}{{{\lambda _2}}}$.........(5)
Putting (4) and (5) in (3) we get
\[\dfrac{{{P_2}}}{{{P_1}}} = {\left( {\dfrac{{b/{\lambda _1}}}{{b/{\lambda _2}}}} \right)^4}\]
\[ \Rightarrow \dfrac{{{P_2}}}{{{P_1}}} = {\left( {\dfrac{{{\lambda _2}}}{{{\lambda _1}}}} \right)^4}\]
According to the question, ${\lambda _1} = 200{\text{nm}}$ and ${\lambda _2} = 600{\text{nm}}$. Substituting these above we get
\[\dfrac{{{P_2}}}{{{P_1}}} = {\left( {\dfrac{{600}}{{200}}} \right)^4}\]
On solving we get
\[\dfrac{{{P_2}}}{{{P_1}}} = 81\]
Thus, the ratio of the power emitted per unit area by source ${O_1}$ to that of source ${O_2}$ is equal to $81:1$.
Note: We have been asked to find out the ratio of the power emitted per unit area, but we have evaluated the ratio of power. This is because the two ratios will be equal as the area will get cancelled from both the numerator and the denominator.
Formula used: The formulae used in solving this question are given by
${\lambda _{\max }} = \dfrac{b}{T}$, here ${\lambda _{\max }}$ is the maximum wavelength at the absolute temperature $T$, and $b$ is a constant.
\[{P_R} = \sigma {T^4}\], here \[{P_R}\] is the radiant power at the absolute temperature $T$, and $\sigma $ is the Stefan-Boltzmann constant.
Complete step-by-step solution:
Let the power emitted by the source ${O_1}$ be ${P_1}$ and that emitted by the source ${O_2}$ be ${P_2}$.
We know from the Stefan’s law that the radiant power is proportional to the fourth power of the absolute temperature. So it is given by
\[{P_R} = \sigma {T^4}\]
If the temperature of the source ${O_1}$ is equal to ${T_1}$, then the radiant power emitted by it is given by
${P_1} = \sigma {T_1}^4$........... (1)
Also, if the temperature of the source ${O_2}$ is equal to ${T_2}$, then the radiant power emitted by it is given by
${P_2} = \sigma {T_2}^4$...............(2)
Dividing (2) by (1) we get
$\dfrac{{{P_2}}}{{{P_1}}} = \dfrac{{\sigma {T_2}^4}}{{\sigma {T_1}^4}}$
\[ \Rightarrow \dfrac{{{P_2}}}{{{P_1}}} = {\left( {\dfrac{{{T_2}}}{{{T_1}}}} \right)^4}\]........(3)
Now, from the Wien’s displacement law we know that the maximum wavelength of the radiation emitted by an object is inversely proportional to its absolute temperature. So it is given by
${\lambda _{\max }} = \dfrac{b}{T}$
$ \Rightarrow T = \dfrac{b}{{{\lambda _{\max }}}}$
If ${\lambda _1}$ is the maximum temperature of the object ${O_1}$ then its absolute temperature is
${T_1} = \dfrac{b}{{{\lambda _1}}}$.........(4)
Also, if the maximum temperature of the object ${O_1}$ then its absolute temperature is
${T_2} = \dfrac{b}{{{\lambda _2}}}$.........(5)
Putting (4) and (5) in (3) we get
\[\dfrac{{{P_2}}}{{{P_1}}} = {\left( {\dfrac{{b/{\lambda _1}}}{{b/{\lambda _2}}}} \right)^4}\]
\[ \Rightarrow \dfrac{{{P_2}}}{{{P_1}}} = {\left( {\dfrac{{{\lambda _2}}}{{{\lambda _1}}}} \right)^4}\]
According to the question, ${\lambda _1} = 200{\text{nm}}$ and ${\lambda _2} = 600{\text{nm}}$. Substituting these above we get
\[\dfrac{{{P_2}}}{{{P_1}}} = {\left( {\dfrac{{600}}{{200}}} \right)^4}\]
On solving we get
\[\dfrac{{{P_2}}}{{{P_1}}} = 81\]
Thus, the ratio of the power emitted per unit area by source ${O_1}$ to that of source ${O_2}$ is equal to $81:1$.
Note: We have been asked to find out the ratio of the power emitted per unit area, but we have evaluated the ratio of power. This is because the two ratios will be equal as the area will get cancelled from both the numerator and the denominator.
Recently Updated Pages
Write a composition in approximately 450 500 words class 10 english JEE_Main
![arrow-right](/cdn/images/seo-templates/arrow-right.png)
Arrange the sentences P Q R between S1 and S5 such class 10 english JEE_Main
![arrow-right](/cdn/images/seo-templates/arrow-right.png)
What is the common property of the oxides CONO and class 10 chemistry JEE_Main
![arrow-right](/cdn/images/seo-templates/arrow-right.png)
What happens when dilute hydrochloric acid is added class 10 chemistry JEE_Main
![arrow-right](/cdn/images/seo-templates/arrow-right.png)
If four points A63B 35C4 2 and Dx3x are given in such class 10 maths JEE_Main
![arrow-right](/cdn/images/seo-templates/arrow-right.png)
The area of square inscribed in a circle of diameter class 10 maths JEE_Main
![arrow-right](/cdn/images/seo-templates/arrow-right.png)
Other Pages
Excluding stoppages the speed of a bus is 54 kmph and class 11 maths JEE_Main
![arrow-right](/cdn/images/seo-templates/arrow-right.png)
In the ground state an element has 13 electrons in class 11 chemistry JEE_Main
![arrow-right](/cdn/images/seo-templates/arrow-right.png)
Electric field due to uniformly charged sphere class 12 physics JEE_Main
![arrow-right](/cdn/images/seo-templates/arrow-right.png)
A boat takes 2 hours to go 8 km and come back to a class 11 physics JEE_Main
![arrow-right](/cdn/images/seo-templates/arrow-right.png)
According to classical free electron theory A There class 11 physics JEE_Main
![arrow-right](/cdn/images/seo-templates/arrow-right.png)
Differentiate between homogeneous and heterogeneous class 12 chemistry JEE_Main
![arrow-right](/cdn/images/seo-templates/arrow-right.png)