The operating temperature of a tungsten filament in an incandescent light bulb is 2450 K, and its emissivity is 0.350. Find the surface area of the filament of a 150 W bulb if all the electrical energy consumed by the bulb is radiated by the filament as electromagnetic waves. (Only a fraction of the radiation ap- pears as visible light.)

A = 2.1 × 10^(-4) m²

Explanation:

We are given;

Temperature; T = 2450 K

Emissivity; ε = 0.35

Bulb rating; H = 150 W

To calculate the surface area, we will use the formula;

H = AεσT⁴

Where σ is stephan boltzman constant with a value of 5.66 × 10^(−8) W/m²⋅K⁴

Making A the subject of the formula, we have;

A = H/εσT⁴

Plugging in the relevant values gives;

A = 150/(0.35 × 5.66 × 10^(−8) × 2450⁴)

A = 2.1 × 10^(-4) m²

the working equation for the angular size is the product of the physical size and 360 degrees divided by the product of two pi and distance from earth. the minimum size would be 0.559 degrees while the maximum size would be 0.49 degrees.