Question

A 120 watt filament lamp loses all its energy by radiation from its surface. The emissivity of the surface is 0.6. The area of the surface is 3.53 × 10⁻³ m². Calculate the temperature of the filament.

Answer 1

Given: P = 120 W

A = 3.53 × 10⁻³ m²

e = 0.6

σ = 5.67 × 10⁻⁸

To find: T = ?

Formula: Energy radiated per unit area is:

`Q/At = eσT^4`

`Q/t = AeσT^4`

`T^4 = Q/(tAeσ)`

= `120/(3.53 xx 10^-3 xx 0.6 xx 5.67 xx 10^-8)`

= `120/(12.0 xx 10^-13)`

= `120/(120 xx 10^-12)`

= 10⁻¹²