# What is the lowest number of polarimeters

## Polarimeter

FACULTY OF PHYSICS, internship for minor subjects

Try 54

Polarimeter

1. The concentration of a cane sugar solution is to be determined polarimetrically.

2. Record the rotation dispersion curve of a quartz.

Basics:

The polarimetric concentration determination is based on the rotation of the plane of vibration linearly

polarized light when shining through an optically active solution. in the Polarimeter it becomes linear

polarized light produced with a NICOL prism (Fig. 1). It consists of two cemented together

Calcite halves that are designed so that the penetrating light due to the birefringence in

the ordinary (o) and the extraordinary (ao) light bundle is split, both of which are linearly polarized.

The ordinary light hits the calcite-cement interface at an angle of incidence α that is greater than

the critical angle of total reflection and is thus eliminated from the beam path.

in the Polarimeter (Fig. 3) the linearly polarized light coming from the polarizer P enters the tube R,

which is filled with the optically active solution. This rotates the plane of vibration of the linearly polarized

Light by an angle δ which is proportional to the concentration c and proportional to the irradiated

Layer thickness l is. For any optically active solution, therefore, is the ratio

δ

= Δ

l ⋅ c

λ, T

(1)

a characteristic material constant called the specific rotatory power and depends on the wavelength

λ of the incident light and the temperature T depends.

In the case of solids, the concentration c of the molecules is a material constant, so that for solids it is optically active

Substances applies:

δ Δ ⋅ l

(2)

= λ, T

The determination of the angle of rotation δ is based on the fact that a second NICOL prism, the analyzer A,

only lets through that component of linearly polarized light that lies in its plane of oscillation. Is

consequently the plane of vibration of the analyzer by ϕ compared to that of the incoming linearly polarized

When the light is rotated, linearly polarized light comes out of the analyzer with the component

'

E = E ⋅ cosϕ (see Figure 2)

'

With ϕ = 90 °, E = 0, i.e. H. with no optically active substance between the

Polarizer P and analyzer A, the field of view of observer B is dark,

when the plane of oscillation of the analyzer is opposite to that of the polarizer

ϕ = rotated 90 ° (crossed NICOLS). Optically active substances consist of

asymmetrically structured molecules, depending on the order of their ligands in the

Molecule the plane of oscillation of linearly polarized light to the left or to the left

Turn right. The direction of rotation, viewed from B, is determined

Execution:

In principle, the analyzer A is first used without optically active substance Polarimeter in the for

Polarizer P brought crossed position. Then you put the filled with the optically active substance

Tube R into the apparatus. The solution rotates the plane of oscillation of the one coming out of the polarizer linearly

polarized light so that the field of vision is brightened. To determine the angle of rotation δ, the

Analyzer A rotated in the direction of rotation of the optically active solution until the field of view is complete again

appears dark.

In order to be able to determine these two positions of the analyzer as precisely as possible, the

Polarization apparatus a third NICOL prism H as a so-called penumbra device between the

Polarizer P and the tube R attached (Fig.3). It divides the field of view of the observation telescope F into

two halves. Compared to the polarizer, the oscillation level of this auxiliary NICOL is insignificant

turned. If you adjust the analyzer so that its plane of oscillation corresponds to that of the polarizer or to the

of the auxiliary NICOL is crossed, one of the two halves of the field of view appears dark and the other

lightened. Between these two positions of the analyzer there is a third one with the same,

weakened brightness of both halves of the field of view, so that the line separating the field of vision disappears Because

the eye reacts particularly sensitively to this, this so-called penumbra setting becomes the determination

of the angle of rotation δ used.

The monochromatic light required for the measurement is produced with a yellow filter G. The

Light source Q is to be shifted along the optical axis until the brightness of the visual field is visible to the eye

appears pleasant. The telescope F is in focus on the field of view separation line caused by H.

to adjust. The analyzer A is now rotated so that both halves of the field of view are equally attenuated

Brightness appear.

This penumbra setting is the zero point for the measurements. Its mean value α 0 is made from at least

10 repeatedly executed settings of the penumbra position are determined.

To 1.): One of the tubes filled with cane sugar solution is inserted into the channel of the Polarimeters used that

Cover of the Polarimeterhousing closed again and the telescope again on the field of view dividing line

focused. Now turn the analyzer into the new half-shadow position α and form from 10

Settings the mean value α

With δ = α - α 0, the concentration of the solution can be determined from relation (1).

With the second tube containing the same solution at the same concentration, the proportionality is

between δ and l.

To 2.): For each of the four color filters, the rotation δ caused by a quartz plate I is determined with the aid of the

to determine the appropriate penumbra settings. The following applies in general to δ:

(α - α 0

) + z ⋅ °

δ = 180, (3)

where z is an integer (> 0), since with this Polarimeter z. B. the rotation angles 20 ° and 200 ° not

can be distinguished. The same measurements are to be carried out with the second quartz plate II. Out

δ

δ

I.

II

l

=

l

I.

II

(4)

- 2 -

z I and z II can be determined if one tries starting with z = 0.

The graphic representation of

δ = f (λ) (5)

is the rotational dispersion curve sought.

Details:

Cane sugar solution

Layer thicknesses of the quartz

Δ λ, r = 6.64 ° cm 2 g -1 l I

= 398 mm

at λ = 589nm l II

= 598 mm

T = 293K

Length of pipes

Filter wavelengths

l 1

= 10cm red λ = 650nm

l 2

= 20cm yellow λ = 590nm

green λ = 530nm

blue λ = 480nm

You will need graph paper for this experiment!

Literature:

Standard textbooks in experimental physics.

________________

Version: May 10

- 3 -

FACULTY OF PHYSICS, internship for minor subjects Experiment 54 Polarimeter Tasks: 1. The concentration of a cane sugar solution is to be determined polarimetrically. 2. Record the rotation dispersion curve of a quartz. Basics: The polarimetric concentration determination is based on the rotation of the plane of oscillation of linearly polarized light when shining through an optically active solution. In the polarimeter , the linearly polarized light is produced with a NICOL prism (Fig. 1). It consists of two calcite halves cemented to one another, which are designed in such a way that the penetrating light is split into ordinary (o) and extraordinary (ao) light bundles due to birefringence, both of which are linearly polarized. The ordinary light hits the limestone-cement interface at an angle of incidence α that is greater than the critical angle of total reflection and is thus eliminated from the beam path. In the polarimeter (Fig. 3), the linearly polarized light coming from the polarizer P enters the tube R, which is filled with the optically active solution. This rotates the plane of oscillation of the linearly polarized light by an angle δ, which is proportional to the concentration c and proportional to the layer thickness l through which the radiation passes. For every optically active solution, the ratio δ = Δ l ⋅ c λ, T (1) is a characteristic material constant that is called the specific rotation capacity and depends on the wavelength λ of the incident light and the temperature T. In the case of solid substances, the concentration c of the molecules is a material constant, so that for solid optically active substances the following applies: δ Δ ⋅ l (2) = λ, T The determination of the angle of rotation δ is based on the fact that a second Nicol prism, the analyzer A , only lets through that component of linearly polarized light that lies in its plane of oscillation. If the oscillation plane of the analyzer is rotated by ϕ compared to that of the incoming linearly polarized light, linearly polarized light with the component 'E = E ⋅ cosϕ (see Fig. 2)' with ϕ = 90 ° would therefore be E = 0, d. H. Without an optically active substance between the polarizer P and the analyzer A, the field of view of the observer B is dark if the plane of vibration of the analyzer is rotated by ϕ = 90 ° with respect to that of the polarizer (crossed NICOLS). Optically active substances consist of asymmetrically structured molecules which, depending on the sequence of their ligands in the molecule, rotate the plane of oscillation of linearly polarized light to the left or to the right. The direction of rotation, viewed from B, is determined

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