Spectro

Mahith Bhima

Physics Lab Report

23 Jan 2017

Spectrometer Aim: To determine the grating constant (N) of the diffraction grating and using that to determine the wavelength separation of the Sodium doublet. Apparatus Required: Spectrometer, sodium vapour lamp, transmission grating. Procedure: Unlock T1 so that the telescope is free to rotate. Direct the telescope to a distant object.Adjust the focus of the telescope until a clear sharp image of the object is obtained through the telescope.This ensures that the telescope is primed to receive the parallel beam of light from the collimator. Now align the telescope with the collimator.Place the collimator in front of the light source.Adjust the collimator until a clear sharp image of the slit aperture is visible through the telescope. Now mount the grating on the holder provided on the turntable.Place the grating perpendicular to the collimator. Align the telescope such that the cross hair of the telescope is centred to the slit.Note down IMT2015024

Page 1

Mahith Bhima

23 Jan 2017

Physics Lab Report

the readings from both left scale and right scales of the vernier scale. Now rotate the telescope right slowly and stop when you get the fringe with two lines. The inner one is for D2 and outer for D1.Take the readings for both.Repeat the process left side. For D2 line, Order (m)

MSR

LHS VSR

(degree)

(minute)

0

180

0

1

197.5

16

-1

162.5

9

θ1

MSR

RHS VSR

(deg+ min)

(degree)

(minute)

0

0

17 46

17.5

10

17 40 17 43

17 21

342.5

21

17 09 17 15

θ2

θavg

(deg+ (deg+mi min) n)

d sin(θ) = mλ N = sin(θ)/mλ

[ N = 1/d ]

N - Grating Constant (lines per inch) θ = 17.71 deg (for m = 1) θ = 17.25 deg (for m = -1) sin(θ) = 0.304 (for m = 1) sin(θ) = 0.296 (for m = -1) N1 = 516132 lines per metre N2 = 502550 lines per metre N = 509341 lines per metre IMT2015024

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Mahith Bhima

23 Jan 2017

Physics Lab Report

N = 12938 lines per inch

Error analysis: ΔN = √( - ^2) ΔN = √46117681 lines per metre ΔN = 6791 lines per metre ΔN = 173 lines per inch Therefore N = 12938 ± 173 lines per inch For D1 line, Order (m)

MSR

LHS VSR

(degree)

(minute)

0

180

0

1

197.5

19

-1

162.5

7

θ1

MSR

RHS VSR

(deg+m in)

(degree)

(minute)

0

0

17 49

17.5

12

17 42

17 45

17 23

342.5

18

17 12

17 17

θ2

θavg

(deg+mi (deg+m n) in)

For D2, θ = 17.71 deg (for m = 1) θ = 17.25 deg (for m = -1) θavg = 17.4833 deg For D1, IMT2015024

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Mahith Bhima

Physics Lab Report

23 Jan 2017

θavg = 17.5166 deg θ = 17.77 deg (for m = 1) θ = 17.30 deg (for m = -1) Δλ = d(sin(θ1)-sin(θ2))/m For m=1, Δλ = d(sin(17.77)-sin(17,71))/m Δλ = 20 Angstroms For m=-1, Δλ = d(sin(17.77)-sin(17,71))/m Δλ = 16 Angstroms Δλ(avg) = 18 Angstroms Standard Deviation for Δλ, ΔΔλ = √( - ^2) ΔΔλ = 2 Angstroms Hence wavelength separation is 18 ± 2 Angstroms λ = 5889 + 18 = 5909 Angstroms for D1 line The wavelength for the D1 line is,λ = 5909 ± 2 Angstroms.

IMT2015024

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