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

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