A tube of length `l = 26 cm` is filled with benzence and placed in a longitudinal magnetic field of a solenoid positioned between two Polaroids. The angle between the principle directions of the Polaroids is equal to `45^(@)`. Find the minimum strength of the magnetic field at which light of the wavelength `589 nm` propagates through that system only in one direction (optical value). What happens if teh idrection of the given magnetic field is changed to the opposite one?

Explanation

There must be a faraday rotation by `45^(@)` in the opposite direction so that light could pass through the second polariod. Thus
`Vl H_(min) = pi//4`
or `H_(min) = (pi//4)/(Vl) = (45 xx 60)/(2.59 xx 0.26) (A)/(m)`
`=4.01 (kA)/(m)`
If the direction of magnetic field is changed then the sense of rotation will also change. Light will be complately quenched in the above case.