Question

Certain substance emit only the wavelength ${\lambda }_1,{\lambda }_2,{\lambda }_{3}and{\lambda }_4$ when it is at a high temperature. When this substance is at a colder temperature, it will absorb only the following wavelength :

• A. ${\lambda }_1$
• B. ${\lambda }_2$
• C. ${\lambda }_1$ and ${\lambda }_2$
• D. ${\lambda }_1,{\lambda }_2,{\lambda }_3$ and ${\lambda }_4$

Answer 1

Answer: (D)

${\lambda }_1,{\lambda }_2,{\lambda }_3$ and ${\lambda }_4$

With the help of kirchhoff's law we can say that $\epsilon =\alpha$
$\epsilon =emissivity$
$\alpha =absorptivity$
so kirchhoff's law state that total emissivity of body is equal to total absorptivity.
so ${\lambda }_1,{\lambda }_2,{\lambda }_3,{\lambda }_4$ will be absorbed.