SSC JE Electrical Engineering 2014 Set 2 Paper

Question : 180 of 200

Marks: +1, -0

Two electric bulbs have tungsten filament of same thickness. If one of them gives 60 W and the other gives 100 W, then :

Solution:

∵

ρ = {RA}/l

Providing same voltage V

P =V^2/ R

∴

P={V^2A}/{ρl}

∴

l={V^2A}/{ρp}

(∵ Both the filament have same thickness. So ‘A’ will be same)
∴

l∝ 1/p

Hence filament of low power will have longer length.

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