Verified Solution • 2025–26 Session
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QJEEAdv16Ph6ddb: JEE Advanced 2016 Physics - Class 12 JEEAdv16Ph6ddb Solution: An incandescent bulb has a thin filament of tungsten that is…
An incandescent bulb has a thin filament of tungsten that is heated to high temperature by passing an electric current. The hot filament emits black-body radiation. The filament is observed to break up at random locations after a sufficiently long time of operation due to non-uniform evaporation of tungsten from the filament. If the bulb is powered at constant voltage, which of the following statement(s) is (are) true?
Multiple Choice Options
- A The temperature distribution over the filament is uniform
- B The resistance over small sections of the filament decreases with time
- C The filament emits more light at higher band of frequencies before it breaks up
- D The filament consumes less electrical power towards the end of the life of the bulb
Step-by-Step Verified Solution
Because of non-uniform evaporation at different section, area of cross-section would be different at different sections.
Region of highest evaporation rate would have rapidly reduced area and would become break up cross-section.
Resistance of the wire as whole increases with time. Overall resistance increases hence power decreases.
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At break up junction temperature would be highest, thus light of highest band frequency would be emitted at those cross-section.