KEAM 2015 Physics and Chemistry Paper

Total energy emitted per second by a unit area of a body is proportional to the fourth power of its absolute temperature.
i.e. ‌‌E=σT4
where, σ is a universal constant called Stefan Boltzmann constant.
Given, ‌‌T1=127∘C
=127∘+273=400K
T2=527∘C=800K
and ‌‌r1=8cm⇒r2=2cm
We know that total energy.
E=σAT4
In the first condition,
E1=σ1A1T14
In the second condition.
E2=σ2A2T24
On dividing Eq. (i) by Eq. (ii), we get ∣∴σ1=σ2]
=‌

82

22

×‌

(400)4

(800)4

⇒‌‌‌

E1

E2

=42×‌

1

24

⇒‌‌‌

E1

E2

=‌

1

1

‌‌ or 1: 1