In the visible region of the spectrum the rotation of the place of polarization is given by `theta=a+(b)/(lambda^2)`. The optical rotation produced by a particular material is found to be `30^@` per mm at `lambda=5000Å` and `50^@` per mm at `lambda=4000Å`. The value of constant a will be

Options

A. (a) `+(50^@)/(9)`permm
B. (b) `-(50^@)/(9)`permm
C. (c) `+(9^@)/(50)`permm
D. (d) `-(9^@)/(50)`permm

Answer

B

Explanation

`theta=a+(b)/(lambda^2)`
`30=a+(b)/((5000)^2)` and `50=a+(b)/((4000)^2)`
Solving for a, we get `a=(50^@)/(9)per mm`