A very small hole in an electric furnace is used for heating metals. The hole nearly acts as a black body. The area of the hole is 200 ~mm ^2 . To keep a metal at 727^ C , heat energy flowing through this hole per sec, in joules is ( =5.67 10⁻⁸ Wm ⁻² ~K ⁻⁴ )

Step-by-step solution

By Stefan's law If the absolute temperature of a black body is T , then the energy E emitted per second per unit surface area of the body aligned & E T^4 & E= A T^4 aligned Given, aligned & =5.67 10⁻⁸ ~W / m ^2 ~K ^4 T & =727+273=1000 ~K A & =200 10⁻⁶ ~m E & =5.67 10⁻⁸ (200 10⁻⁶ ) (1000)^4 & =5.67 2 10⁻¹² 10¹² & =11.34 ~J / s aligned