Q. Specific rotation of sugar solution is 0.01 SI units. $200kgm^{- 3}$ of impure sugar solution is taken in a polarimeter tube of length $0.25m$ and an optical rotation of $0.4\ rad$ is observed. The percentage of purity of sugar is the sample is
A) 80%
B) 89%
C) 11%
D) 20%
Explanation
(a) Specific rotation
$(\alpha) = \frac{\theta}{lc} \Rightarrow c = \frac{\theta}{\alpha l} = \frac{0.4}{0.01 \times 0.25} = 160kg/m^{3}$
Now percentage purity of sugar solution
$= \frac{160}{200} \times 100 = 80\%$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.