18-05-2012, 12:47 PM
Engineering Physics Laboratory Manual For B.E. III Semester.pdf (Size: 491.99 KB / Downloads: 794)
1 Diffraction grating
2 Transistor characteristics
3 Zener diode characteristics
4 Stefan?s law
5 Fermi energy
6 Series and Parallel LCR Circuits
7 Planck?s constant
8 Energy gap of a semiconductor
9 Dielectric constant
10 B-H Curve
11 Ultrasonic interferometer(Demo)
Diffraction Grating
Aim:
To determine the wavelength of the prominent spectral lines of the mercury spectrum using a diffraction grating.
Apparatus: Spectrometer, spirit level, mercury lamp, grating, magnifying lens etc.
Formula: The wavelength of a spectral line is given by,
m
n
D CSin ÷
ø
ö
çè
æ
= 2
2
l
l : wavelength of the spectral line (m)
N : number of lines per meter on grating
C : grating constant = 1/ N (m)
D: angle of minimum deviation for a spectral line (degree)
n : order of the spectrum ( n = 1)
Procedure: Preliminary adjustments are done for the spectrometer. The spectrometer is
placed in front of the sodium vapor lamp and its position is so adjusted that the collimator slit is
illuminated with sodium light which is confirmed by viewing the slit through the collimator. The
telescope is brought in line with the collimator. The rack and pinion arrangement of the
collimator is adjusted until clear image of the slit is seen through the telescope. The grating is
mounted on the grating table using grating holder. The telescope is rotated either to the right
or to the left until the spectral lines of first order spectrum are seen. Now the grating is set to
the minimum deviation position. The vertical crosswire of the telescope is set to one of the
edges of Yellow2 line. The spectrometer reading is noted. The same is repeated for Yellow1,
Green, Blue and Violet lines by adjusting the crosswire for the same side edges ®. The Central
Bright Maximum is focused. The vertical cross wire is set on the Central Bright Maximum and
the reading is noted (the Direct Reading R0). The readings are tabulated. The difference in the
reading R and R0 for the each color gives the angle of minimum deviation (D) for the
corresponding color. The grating constant is determined given the value of number of lines per
meter on the grating. The wavelength of the spectral line is calculated using the formula.