27 * Stefan Boltzmann law is applicable for heat transfer by (1 ) Radiation O Conduction and radiation combined O Conduction O Convection O 28 The ratio of the emissive power and absorptive power of all bodies is the same and is equal to * the emissive power of a perfectly black body. This statement is known as (1 ) Planck's law Krichoff's law Wien' law O Stefan's law temperature Fourth power of temperature Fourth power of absolute temperature 26 * In free convection heat transfer, Nusselt number is function of (1 ) .Prandtl no. and Reynold no Grashoff no. and Reynold no .Grashoff no. and Prandtl no Grashoff no.. Prandtl no and Reynold no 27 *Stefan Boltzmann law is applicable for heat transfer by (1 )