Question

Consider the following statements: 

 An ordinary light bulb has a rather short life because the: 

1. filament wire is not uniform. 

2. bulb cannot be evacuated completely. 

3. wires supporting the filament melt at high temperatures. 

Which of the above statements are correct? 

(a) 1 and 3 (b) 2 and 3 (c) 1 and 2 (d) 1, 2 and 3

Answer 1

(d) The electric light bulb uses a glowing wire filament heated by electrical resistance to white to generate light (a process known as thermal radiation). The 'bulb' is the glass enclosure which keeps the filament in a vacuum or low-pressure noble gas. Complete evacuation of bulb is not possible. A small quantity of gases left behind which expands on heating by heat through filament. Moreover, the wires supporting the filament sometimes melt due to high heat generated as a result of high resistance of filament. Thus, these factors leads to short life span of ordinary bulb.