Why a black body at 1000K is red hot whereas it is white hot at 2000K. 

Red hot: 1000K, the peak wavelength emitted by a black body falls within visible red range making the black body appear red hot.

White Hot: At 2000K, the black body produces a mixture of peak wavelengths with colors in the visible spectrum including red, yellow, green, and blue, which combine to produce white light. Thus, the black body appears white hot.

Thanks

Dr. Bbosa Science