Consider the following statements : An ordinary light bulb has a rather short life because the I. filament wire is not uniform. II. bulb cannot be evacuated completely. III. wires supporting the filament melt at high temperatures. Which of the above statements are correct ?

An ordinary incandescent bulb fails early chiefly because of weak spots in the filament and effects of residual gases. Non-uniformities or microscopic thin spots in the filament cause local overheating and breakage (leading to short life). Also, bulbs cannot be evacuated perfectly; residual gas and imperfect evacuation accelerate tungsten loss/oxidation and bulb blackening, shortening life—hence inert or halogen fills and getters are used to reduce these effects [1]. The supporting lead-in wires are typically made of high‑temperature metals (e.g., molybdenum) designed to retain strength at filament temperatures, so melting of support wires is not a primary cause of ordinary bulb failure [2]. Therefore statements I and II are correct, III is incorrect.

Sources

1. [1] https://www.e-education.psu.edu/egee102/node/2035
2. [2] https://physlab.org/wp-content/uploads/2016/03/Planck_ref8.pdf