Question

Calculate the rate of energy emitted from an incandescent tungsten halogen light bulb as a function of wavelength (W/m2 per µm versus wavelength in µm). Assume the tungsten filament has a temperature of 3300 K.

c. What fraction of the total energy emitted by the bulb produces light that we can see and what fraction is wasted as heat (λ > 800 nm)?

d. Compare total area under your emissive power plot to theoretical area. Given the total power emitted (area under curve) estimate the surface area of the tungsten filament if the bulb is rated for 100 watts

Answer 1

, where

Where is emissivity ; h= plancks constant.c = velocity of light ;T= temerature in K ; k = boltzman constant

The factor = 3.74 X 10^(-16) W/m^2 and C2 = 1.44 X 10^(-2) mK

Applying these values we find on excel sheet values of Emissivity for various values of Wave-length in micro-meters

The area under can also be found by

= 5.67 X 10^(-8) W/m^2 K X (3300)4 = 6.72 X 10^6 watts/m^2

In comparison the area under curve we get is 2.55 X 10^9 watts/m^2

6.72 X 10^6 X Area of filament = 100 watts

Area = 100 w/6.72 X 10^6 = 14.9 X 10^ (-6) m^2