Why are equivalent bulbs filled with chemically inactive nitrogen or argon gas?
(b) The resistance of a wire of 0.01cm radius is `10 Omega`. If the resistivity of the material of the wire is `50 times 10^-8 Omega.m` Find the length of the wire.

Explanation

Electric bulbs are generally filled with some inert gas like nitrogen or argon. This enables to prolong the life of the filament of electric bulb.
(b) Here radius of wire r=0.01 cm =`0.01 times 10^-2 m` resistance R=`10 Omega` and resistivity `rho=0 times 10^-8 Omega.m`
As `R=(rho L)/A=(rho L)/( pi r^2)`, hence length `L=(R pi r^2)/( rho)`
`implies L= (10 times 22 times (0.01 times 10^-2)^2)/(7 times 50 times 10^-8)=22/35 m=0.629m or 62.9 cm`