Question

Light passes successively through two polarimeter tubes each of length $0.29m$. The first tube contains dextro rotatory solution of concentration, $60kg{m}^{-3}$ and specific rotation $0.02rad{m}^{2}k{g}^{-1}$ . The second tube contains laevo rotatory solution of concentration $30kg{m}^{-3}$ and specific rotation $0.02rad{m}^2{k}^{-1}$. The net rotation produced is

• A. $0^o$
• B. ${15}^o$
• C. ${10}^o$
• D. ${20}^o$

Answer 1

Answer: (A)

$0^o$

$\text{Dextrorotatory}$ means a compound that rotates the plane of polarized towards right or clockwise.

$\text{Laevorotatory}$ means a compound that rotates the plane of polarized towards left or anti-clockwise.

Rotation produced $\theta =S\times l\times c$
where $\theta$ is rotation angle measured in degree, $S$ is specific rotation, C is the concentration of the solution.

Net, rotation produced

${\theta }_r={\theta }_1-{\theta }_2=l(S_1{c}_1-S_2{c}_2)$

$=0.29\times [0.01\times 60-0.02\times 30]=0$

Hence, net rotation produced is zero.