Switch On/Off Light : Used to switch on/off the light.
Place Prism/Remove Prism : This switch used to place the prism on the prism table or remove prism from the prism table.
Slit focus : This slider used to focus the slit while looking through telescope.
Slit width : Using this slider, width of the slit can be adjusted.
Telescope: Using this slider one can move the telescope from its position.
Vernier Table: Vernier table can be rotate using this slider.
Fine Angle adjustment
Telescope: This is used to fine adjust the telescope.
Vernier Table: Using this slider , we can rotate fine angle.
Here we get the zoomed view of vernier I and II by placing mouse pointer over it.
- Focus Telescope on distant object.
- When focus is correct, start button is activated. Then click Start button.
- Switch on the light by clicking Switch On Light button.
- Focus the slit using Slit focus slider.
- Adjust the slit width using Slit width slider.
- Coincide the slit with cross wire in the telescope.
Performing Real Lab:
- Turn the telescope towards the white wall or screen and looking through eye-piece, adjust its position till the cross wires are clearly seen.
- Turn the telescope towards window, focus the telescope to a long distant object.
- Place the telescope parallel to collimator.
- Place the collimator directed towards sodium vapor lamb. Switch on the lamp.
- Focus collimator slit using collimator focusing adjustment.
- Adjust the collimator slit width.
- Place prism table, note that the surface of the table is just below the level of telescope and collimator.
- Place spirit level on prism table. Adjust the base leveling screw till the bubble come at the centre of spirit level.
- Clamp the prism holder.
- Clamp the prism in which the sharp edge is facing towards the collimator, and base of the prism is at the clamp.
Least Count of Spectrometer
One main scale division (N) =................minute
Number of divisions on vernier (v) = ................
L.C = = .......................minute
Procedure for Real lab
The telescope is brought in line with the collimator and the image of the slit is viewed through it. The telescope is adjusted to make the vertical cross wire coincides with the image of the slit. The readings of anyone of the verniers is taken. To set the prism for angle of incidence i of the telescope is rotated through an angle θ = (180-2i) from the direct reading position and clamped. The prism is mounted on the prism table with its grounded face towards the clamp and is rotated so that its reflecting edge is turned away from the collimator.
Looking through the telescope, the vernier table is rotated as that reflected image of the slit coincides with the vertical crosswire. Now the angle of incidence is equal to I. The vernier table is then fixed.
The telescope is released and is rotated so that the refracted image of the slit is obtained at the vertical cross-wire. The telescope is then fixed in this position. Looking through the telescope with vernier table is rotated in such a direction that the refracted image moves towards the minimum deviation position and then returns to the vertical crosswire. Now, the deviation is the same as before: but the angle of incidence is i’. The vernier is clamped. The telescope is released and rotated to obtain the reflected image of the slit at the crosswire. The telescope is fixed and the reading of both the verniers are taken. The telescope is released and is brought to obtain the direct image at its cross wire. The readings of both verniers are taken. The difference between the reflected reading and direct reading θ2 is found. Now θ2 = (180-2i’). Thus
The experiment is repeated for various values of I and I’ is calculated in each case.
A graph is drawn with angle of incidence i along X-axis and the angle of emergence i' along Y-axis. The graph is a rectangular parabola. from it, angle of incidence corresponding to minimum deviation is calculated.
Observations and Calculations
The angle of emergence i' for various angle of incidence = .........................