An electric bulb has a solid cylindrical filament of length `l` and radius `r` and it consumes power P when connected to a power source. Another bulb having cylindrical filament of same material, operating at same voltage and emitting the same spectrum of light consumes `8 P` power. find length and radius of the new filament. Assume that the filaments do not radiate from the flat ends and radiation is the only source of heat loss from the filaments.

Answer

`2l,4r`