PHYSICS EXPERIMENT 1

EXPERIMENT NO. 1

Object: - To determine the specific rotation of cane sugar solution with the help of polarimeter.

Apparatus Required: - Polarimeter, a balance, measuring cylinder, beaker, source of light and   polarimeter tube.

Formula used: - The specific rotation of the plane of polarization of sugar dissolved in water can be determined by the following formula.

                                               

                                    Where, q = rotation produced in degrees.

                                                   = length of tube in decimeter.

                                                 m = mass of sugar in gms dissolved in water.

                                                 V  = volume of sugar solution.

Figure

                                                                                             

Procedure: -

1.      If the polarimeter is employing a half shade device, a monochromatic source should be used and if bi quartz device is used then white light can be used.

2.      Take the polarimeter tube and clean well both the sides such that it is free from dust. Now fill the tube with pure water and see that no air bubble is enclosed it. Place the tube in its position inside the Polarimeter.

3.      Switch on the source of light and look through the eyepiece. Two halves of unequal intensity is observed. Rotate the analyzer until two halves of the field appears equal bright. Take the reading of main scale as well as vernier scale and find out the total reading.

4.      Prepare the sugar solution of unknown strength. The procedure for preparing it can be seen under the heading observations.

5.      Take the polarimeter tube and remove the pure water and fill it with the prepared sugar solution and again place it in the polarimeter.

6.      Rotate the analyzer to obtain the equal intensity position, first in clockwise direction and then in anti-clockwise direction.

[When the tube containing sugar solution is placed in the path of the polarized light, the plane of polarization is rotated which disturbs the previous position.] 

Note down the position of the analyzer on main and vernier scales in the two directions. Find the mean reading. The difference between this and previous reading gives the specific rotation.

7.      Repeat the experiment with the sugar solutions of different concentrations.

8.      Measure the length of the tube in centimeters and change it in decimeters.

Observation: -            1.    Least count of polarimeter = 0.1 deg

                                   2 .   Length of polarimeter tube = 2.1 dm

                                               

Analyzer reading with pure water
Clockwise			Anticlockwise			A= (X+Y)/2 deg
M.S.	V.S.	Total X deg	M.S.	V.S.	Total Y deg

Concentra-tion of sugar solution	Analyzer reading with sugar solution
	Clockwise			Anticlockwise			B = (X'+Y')/2 deg	q=A~B
	M.S.	V.S.	Total X' deg	M.S.	V.S.	Total Y'        deg

Calculations: -

                                = ---------------deg/dm/kg/m³

Result: - The specific rotation for cane sugar at a room temperature using monochromotic light is ----------

Percentage error:

                                                                                                                                                                                (Standard value~ Observed Value) X 100

                  % ERROR =

                                                                    Standard Value

Precaution:-  

                             1.   The polarimeter tube should be well cleaned.

2.      Whenever solution is changed, rinse the tube with the new solution under   examination.

3.      The position of analyzer should be set accurately.

4.      The temperature and wavelength of light used should be stated.

5.      Reading should be taken when halves of the field of view becomes equally illuminate.

Viva Questions

Ques 1 . What do you mean by polarization?

Ans.  The lack of symmetry about the direction of propagation of light is known as the polarization of light.

Ques 2. What are optical rotations?

Ans .   The rotations produced by a decimeter long column of the liquid containing 1 gm of active substance in 1 cc of the solution.

 Ques 3, What is Brewster’s law of polarization?

 Ans. The tangent of the polarizing angle is mathematically equal to the refractive index of the     material i.e µ = tan (i_p)

 Ques 4.  Define plane of vibration and plane of polarization.

 Ans. The plane of polarization is that plane in which no vibrations occur and the plane in which vibrations occur known as plane of vibration. The vibrations occur at the right angle to the plane of polarization.

Ques 5. What do you mean by double refraction?

Ans. When a ray of light is refracted by a crystal of calcite it gives two refractive rays .this phenomenon is known as double refractions.

 Ques s6. What is nicol prism?

 Ans. It is an optical device which is made by calcite crystal to produce and analyze the plane polarized light .

 Ques 7. What do you mean by Snell’s law?

 Ans. The sine of the angle of incidence to sine of the angle of refraction is equal to the refractive   index of the material.

Ques 8.What is mean by plane polarized and unpolarized light?

Ans. The plane polarized light is the light in which the vibrations take place only along one straight line perpendicular to the direction of propagation of light while in unpolarized light vibrations take place along all possible straight lines perpendicular to the direction of propagation of light.

Ques9. What are the ordinary and extra ordinary lights?

Ans .Ordinary light obeys Snell’s law while extra ordinary doesn’t obey the Snell’s law.

Ques10. Define refractive index.

Ans. It is the ratio of velocity of light in vacuum to the velocity of light in any medium.

µ = c / v