A metal rod at a temperature of 150 degree Celsius, radiates energy at arate of 20W. If its temperature is increased to 300 degree celsius,then it will radiate at a rate of about?
1. 40.8 W
2. 17.5 W
3. 68.3 W
4. 37.2 W
Please explain the answer as well.

Asked by mamalinanda1998 | 15th May, 2016, 04:27: PM

Expert Answer:

begin mathsize 12px style According space to space the space Stefan apostrophe straight s space law comma space straight E space equals space straight sigma space straight T to the power of 4
When space the space temperature space of space the space body space is space raised space from space straight T space to space straight T apostrophe comma space then space the space new space rate space of space emission space will space be space
straight E apostrophe space equals space straight sigma apostrophe space straight T apostrophe to the power of 4 space
fraction numerator straight E apostrophe over denominator straight E end fraction equals fraction numerator straight T apostrophe over denominator straight T end fraction
fraction numerator straight E apostrophe over denominator 20 space straight W space end fraction equals fraction numerator left parenthesis 573 right parenthesis to the power of 4 space straight K over denominator left parenthesis 423 right parenthesis to the power of 4 space straight K end fraction
On space solving space we space get
straight E apostrophe space equals space 67.3 space straight W end style

Answered by Yashvanti Jain | 16th May, 2016, 07:17: PM