An old lightbulb draws only 50.0 W, rather than its original 60.0 W, due to evaporative thinning of its filament. By what factor is its diameter reduced, assuming uniform thinning along its length? Neglect any effects caused by temperature differences.
The final diameter or radius becomes 0.91 times the initial diameter. So it is reduced by,
Reduction in diameter = (1-0.912) 100%
Hence, the final diameter is reduced by 8.8 %