Question

Temp. of black body is $3000K$ when black body cools. Then change in wavelength $\Delta \lambda =9$ micron corresponding to maximum energy density. Now temp. of black body is:

• A. $300K$
• B. $2700K$
• C. $270K$
• D. $1800K$

Answer 1

The correct option is A $300K$

Wien's displacement law

${\lambda }_1{T}_1={\lambda }_2{T}_2=b=2.8\times {10}^{-3}k$

$\Rightarrow 3000{\lambda }_1=T_2{\lambda }_2\cong 3\times {10}^{-3}km$

${\lambda }_1=1\mu m$ & $({\lambda }_2-{\lambda }_1)=9\mu$

${\lambda }_2=10mum$

$T_2=300K$