# Rotation of PPL by opticaly active compounds (mathematical feeling)

 P: 69 i read formulae in textbook : [α]λt°C = Θ/L*C ........(i) where Θ is rotation in light and L is length of tube and C is concentration in gm/litre if we consider tube of lenth L and cross section area 'A' then C= M/A*L M is mass of sample so (i) becomes [α]λt°C = Θ/[M/A] so are scientist so blind to observe or i am doing something wrong.
 Sci Advisor Thanks PF Gold P: 1,908 This appears to be a variation on Verdet's equation for measuring the concentration of an optically active substance, allowing for temperature variations. You have neatly removed the variable for concentration.
 Sci Advisor P: 3,593 To blind to observe what? Your formula is correct, however, I doubt that it is more practical. The point is that you would have to fill the sample of the given mass in a tube which has precisely the cross section you sprecified. Have you tried to fill a tube with precisely the amount of substance you want and to put glass windows on it without neither liquid spilling out or gas bubbles remaining inside?
P: 69
Rotation of PPL by opticaly active compounds (mathematical feeling)

 Quote by DrDu To blind to observe what? Your formula is correct, however, I doubt that it is more practical. The point is that you would have to fill the sample of the given mass in a tube which has precisely the cross section you sprecified. Have you tried to fill a tube with precisely the amount of substance you want and to put glass windows on it without neither liquid spilling out or gas bubbles remaining inside?
DO IMPROVIZE MY LAST STATEMENT I WANT TO ASK:
the older equation has a feeling that if length of tube is increased one of factor will have to change and my equation marks that rotation(θ) and [α] are both independent of length of tube. I am just a bit confused for example help out with this

Q) if length of tube is doubled what will be the effect on Θ?
 Sci Advisor P: 3,593 Depends on what you hold constant. If M is constant, nothing, if c is constant, theta will double.

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