Question

An electric bulb with tungsten filament having an area 0.3 cm² is raised to a temperature of 2727°C, when a current passes through it. Calculate the electric power being consumed n watt if the emissivity of the filament is 0.35. stefan's constant,σ = 5.67 x 10^-5 erg cm^-1 s^-1 K^-4. Given 1ω = 107 ergs s^-1.

Answer 1

Area, A = 0.3 cm² = 0.3 x 10^-4 m²

Temperature, T = (2727 + 273) K = 3000 K

σ = 5.67 x 10^-5 erg cm^-2 s^-1 K^-4

= 5.67 x 10^-8 Jm^-2 s^-1 K^-4.

Power consume = Area = σT⁴

= 0.3 x 10^-4 x 0.35 x 5.67 x 10^-8 x (3000)⁴ Js^-1 or W.

= 48.22 W.