Question

The filament of 40 W electric lamp of length 0.1m and diameter 0.1mm is kept at a temperature of 2773 K. Calculate the emissive power if all the heat is lost by radiation. σ = 5.67 × 10^-8 Wm^-2 K^-4 ].

Answer 1

P = 40 W,

l = 0.1 m,

r = 0.05 mm

T = 2773 K

e = ?

Area = 2π rl =3.142 x 10^-5 m²

Energy emitted by a source in t sec

E = e A σ T⁴ t

\(\frac{E}{t}\)= e A σ T⁴

P = e A σ T⁴

= 0.3798