Question

how is normal incidence position adjusted

Answer 1

The preliminary adjustments of the spectrometer are made. The grating is set for normal incidence. The slit is illuminated by mercury vapour vamp. The telescope is brought in a line with the collimator and the direct image of the slit is made to coincide with the vertical cross wire. The readings of one vernier are noted. The vernier table is firmly clamped. Now, the telescope is rotated exactly through 90° and is fixed in this position. The grating is mounted vertically on the prism table with its ruled surface facing the collimator. The vernier table is released and is slowly rotated till the reflected image coincides with the vertical cross wire. The leveling screws are adjusted so that the image is at the centre of the field of view of the telescope. The prism table is fixed and after making fine adjustments with the tangential screw, the readings of the vernier are noted. Now, the angle of incidence is 45°. The vernier table is then released and rotated exactly through 45° in the proper direction so that the surface of the grating becomes normal to the incident light. The vernier table is firmly clamped in this position.

Answer 2

ok here is ur ans ok