PRISM SPECTROMETER

 

What is a prism-spectrometer?

A prism spectrometer is an optical spectrometer that uses a dispersive prism as its dispersive element. The prism refracts light into its different colors (wavelengths). The dispersion occurs because the angle of refraction is dependent on the refractive index of the prism's material, which in turn is slightly dependent on the wavelength of light that is traveling through it.

Aim of this practical : 

1. Determine the value of the minimum deviation angle of a given prism.

2. Calculate the prisms' refractive index.

Objectives of this practical :

1. Introduce the prism-spectrometer

2. How to calibrate a spectrometer

Let's begin the practical :

Here is the quiz :

BACK TO SCHOOL QUESTIONNAIRE

BEFORE THE VIDEO

  1. Have you seen a Prism-Spectrometer? Yes/No

  2. Where have you seen this apparatus then?

Internet

At school lab

  3. Have you done this practical that was included for your syllabus?  

 Yes/No

  4. Which way as mentioned below?

Chalk & board

Powerpoint presentation

None of the above

  5. What the practical was about? (Name only)

 

After the video

1.     What the practical was about? (Name only)

2.     Name the steps of the calibration. (3 main steps)

3.     Give a brief description (In 5 0r 7 sentences)

4.     i)  How do you get the readings? (In 3 sentences)

             ii) Calculate & get the final 2 angles

 

Prism angle:

Position 1		Position 2
L.H.S	R.H.S	L.H.S	R.H.S
3600 ± 25¢	1600 ± 9¢	1780 ± 32¢	1380 ± 24¢

 

Straight line:

L.H.S	R.H.S
2000 ± 10¢	(200 ± 8¢)+3600

 

Minimum Deviation angle:

L.H.S	R.H.S
1200 ± 8¢	3400 ± 6¢

 

            5.     Draw the graph pattern below.

MODEL ANSWERS (AFTER THE VIDEO)

            1.  Determine the minimum deviation angle & the refractive index of a given prism.

            2. Telescope focusing, Height setting, Table setting

            3.      1)  Focus the telescope – align the telescope with the collimator & obtain a 

                       clear slit

                        2) Do the height setting – adjust the table height until the slit image can’t 

                      be seen & lock the table.

                   3) Do the table setting – adjust the 3 screws on the table & until the slit 

                       image coincides with the cross wires.

                   4) Take the telescope readings for prism angle.

                   5) Place the prism on the table’s center. Get a clear slit image by focusing the 

                       telescope & the collimator, multiple times.

                   6) Obtain the minimum deviation moment by rotating both the telescope & the

                       table to the same direction at the same time.

                   7) Calculate the prism angle & minimum deviation angle by the readings.

         4. i)  1)  Rotate the telescope until the cross wires coincide with the slit image.

                        2) Lock the telescope by the telescope lock screw.

                        3) Take the reading with the minimum error values as well.

                                280° ± (1¢ x 20)  =  280° ± 20¢

             ii) Prism Angle: 

                  Minimum Deviation Angle:

              Refractive index:

                A - Prism angle

                Dm - Minimum Deviation Angle 

                n - Refractive Index of the prism