Q. The density of a gas filled electric lamp is $0.75\ kg/m^{3}$. After the lamp has been switched on, the pressure in it increases from $4 \times 10^{4}$ Pa to $9 \times 10^{4}$ Pa. What is increases in $U_{rms}$?
A) 100
B) 300
C) 200
D) 400
Explanation
(c)
$u_{1} = \sqrt{\frac{3p}{d}}$
$\therefore\ \mathrm{\Delta}u_{rms} = \sqrt{\frac{3}{d}} \times (\sqrt{p_{2}} - \sqrt{p_{2}})$
$= \sqrt{\frac{3}{0.75}} \times (300 - 200)$
$= \sqrt{4} \times 100 = 200$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.