SI.No Name of the Experiments

MEASUREING INSTRUMENTS

M1 VERNIER CALIPER

M2 SCREW GAUGE

M3 TRAVELLING MICROSCOPE

M4 SPECTROMETER

PHYSICS LABORATORY - I

1.(A)

1.(B)

1.(C)

LASER PARAMETERS

PARTICLE SIZE – DETERMINATION BY DIODE LASER

DETERMINATION OF NUMERICAL APERTURE AND

ACCEPTANCE ANGLE – OPTICAL FIBER

2. SPECTROMETER - GRATING

3.

THERMAL CONDUCTIVITY OF A BAD CONDUCTOT –

LEE’S DISC

4.

AIR - WEDGE

5. ULTRASONIC - INTERFEROMETER

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M1 SCREW GAUGE

ZERO ERROR & ZERO CORRECTION

Pitch = Distance moved by the head scale on the pitch scale

No .of the Rotations given

LEAST COUNT = Pitch / Total no.of divisions on the head scale = 1 m.m / 100

L.C = 0.01 mm or 0.01×10-3

m

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M2 VERNIER CALIPERS

Jaws in different

positions

LEAST COUNT = 1 Main scale division – 1 Vernier scale Division

= 1MSD – 1VSD

Value of 1 MSD = 1/10 cm = 0.1×10-2

m

No of divisions on vernier scale = 10

9MSD = 10VSD ; 1VSD = (9/10)MSD = (9/10)(1/10) = 9/100 cm

Therefore L.C = 0.01 cm or 0.01×10-2

m

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M3 TRAVELLING MICROSCOPE

Least count = 1MSD – 1VSD

20 MSD = 1cm

Value of 1 MSD = 1/20 cm = 0.05 cm

No.of divisions in vernier scale = 50

50VSD = 49 MSD

Therefore 1VSD = (49/50)MSD = (49/50)0.05 = 0.049

LC = 0.05 – 0.049 = 0.001 cm ]

L.C = 0.001×10-2

m

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M4 SPECTROMETER

Least count.

20 MSD = 10°

1MSD = 1°/ 2 = 0.5° = 30’

LC = 1MSD – 1VSD

No of Divisions in Vernier scale = 30

30VSD = 29MSD

1VSD = (29/30)MSD = 29’

LC = 30’ – 29’

LC = 1’( ONE MINUTE)

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E 01 SEMICONDUCTOR LASER

Aim:

a. To determine the wavelength of the Laser light.

b. To determine the size of the particle.

c. To find out acceptance angle and Numerical aperture of the fiber.

Apparatus Required:

Diode laser, Fine micro particles nearly like same size ( Lycopodium powder), Glass plate,

Screen , Meter scale

Formula:

a. Wavelength of the Laser source = sin n m

b. Particle size d is given by d = nD / xn m

c. Acceptance angle r / d

Numerical aperture NA = sin

Angle of the diffraction degree

N = Number of lines per meter in the grating

n = order of diffraction.

Wavelength of laser light used. m

D = distance between glass plate and the screen. m

xn = Distance between central bright spot and the nth

ring. m

r = Radius of the circular image. m

d = Distance from fiber end to circular image.m

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Wavelength of LASER

Size of the particle

Diffraction pattern

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Angle of divergence

Numerical Aperture

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Procedure:

a. Wavelength of the Laser source

The grating is kept in between the source and the screen at a distance , D, from the

screen. When the laser beam passes though the grating, diffraction occurs and spots are

seen on the screen.

The positions of 1st , 2

nd , 3

rd ……. Order spots are measured from the central (direct)

spot by measuring on both sides.

b. Particle size.

The grating is removed and a glass plate on which lycopodium powder is sprinkled is

placed. Its position is adjusted to clear diffraction rings. The radii of 1st, 2

nd, 3

rd, .order

rings are measured. If D1 is the distance between the glass plate and screen, the size of

the particle

c. Acceptance angle and Numerical aperture

One end of the fiber is connected to the source and the other end to a NA jig Light

through the fiber passes the aperture of the Jig and a circular patch is seen on the screen.

The opening is slowly closed so that the circular patch just cuts. If r is the radius of

opening and l is the distance between jig and fiber tip , the acceptance angle = r/l and

NA = Sin. This is repeated for different l.

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DETERMINATION OF WAVELENGTH OF LASER LIGHT SOURSE-

OBSERVATIONS

Distance between grating and screen (D) = ……………… cm = ………………. x 10-2

m

Number of lines in grating per meter = …………………………lines / meter

Particle size determination – observation

S.No

Order of

diffraction

(n)

Readings for the diffracted image

Mean

θ λ

Left side Right side

Distance of

different

orders (Xn)

from the

central spot

Tan θ1 θ1

Distance

of

different

order

(Xn) from

the spot

Tan θ2 θ2

Unit cm cm (nm)

1. 1 X1= X1=

2. 2 X2= X2=

3. 3 X3= X3=

4. 4 X4= X4=

SI.NO.

Distance between

screen and glass

plate (D)

Order of

diffraction

n

Distance between

the central bright

point and nth fringe

xn

Particle size

Unit Cm cm cm

1

1

2

3

2

1

2

3

3

1

2

3

Mean = ………………………….. KININDIA

Wavelength of laser source λ = 6900 A˚

= 6900 x 10-10

meter

To determine acceptance angle and numerical aperture

S.No.

Distance from

the fiber end to

circular image

‘d’

Radius of the

circular image ‘r’

Acceptance

angle

NA = sin θa

Mean

Result:

Wavelength of the laser light source = ---------------- m

Average size of the particle = -----------------------m

Numerical aperture of the optical fiber = ------------

Acceptance angle of the optical fiber = --------------

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E 02 - SPECTROMETER (GRATING)

Aim: To determine the wavelength of the lines of the mercury spectrum.

Apparatus Required: Spectrometer, Grating , Sodium vapour lamp , Mercury

vapour lamp, Reading lens.

Formula:

The number of lines of grating = N = Sins n

s = wavelength of the sodium light

n = order of diffraction

Angle of diffraction

The wavelength of the prominent spectral

Lines of the mercury spectrum

Hg = Sinn N 10-10

m

Procedure: Preliminary adjustments are made with the spectrometer. The direct ray is made to

coincide with the vertical crosswire of the telescope. The vernier scales are adjusted to read 00

and 1800. The telescope is rotated through 90

0 and fixed. The grating is mounted on the grating

table and adjusted so that the reflected ray coincides with the cross wire. The vernier table is

rotated through 450. Now, the light is incident normal to grating. This is normal incidence.

The slit is illuminated with sodium vapor lamp. The telescope is released and rotated to get the

diffracted light on either side (left & right). The readings are taken on Vernier A and Vernier B. KININDIA

The difference in readings on both the scales for the two sides gives 2. Hence is noted.

Next the sodium lamp is replaced by Hg lamp and for each line is measured as before and

for each line is calculated from the relation

Determination of wavelength of various spectral lines – Spectrometer readings

N = ………………..lines/metre Order of the spectrum n = ……1….

Total readings (TR) = MSR +(VSR x LC) Least count (LC) = 1’

Spectral

lines

(colours)

Reading for the diffracted image Diffference

between the

readings Mean

2θ

Mean

θ λ

Left side Right side

Vernier A

A1 Vernier B B1 Vernier A A2 Vernier B B 2 2θ

A1~A2

2θ

B1~B2 MSR VSC TR MSR VSC TR MSR VSC TR MSR VSC TR

deg div deg deg Div deg deg div Deg deg div deg

Violet-1

Violet-2

Blue Bluiesh

Green

Green

Yellow-

1

Yellow-

2

Red

Result:

The wavelength of the prominent spectral lines in the mercury source are calculated and

tabulated. KININDIA

E 03 - Lees disc

Aim: To measure the thermal conductivity of a bad conductor (Cardboard,

Glass etc)

Apparatus Required: Lees Disc apparatus, Bad conductors, Thermometers, Stop-clock, Steam

boiler, Screw gauge, Vernier calipers

Formula: Thermal conductivity of a bad conductor.

MS { d dt } .d ( r + 2h)

K = ------------------------------- Wm-1

K-1

R2 ( 1 - 2 ) ( 2R + H)

M = mass of the disc

S = specific heat of the disc

D = thickness of the bad conductor (m)

R = radius of the disc (m)

H = thickness of disc (m)

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Procedure:

This consists of a hot chamber and a metal disc. The material is placed in between the chamber

and the metal disc.

Steam from water heater is passed through the chamber. Heat is conducted to the disc through

the bad conductor. The steady state temperature 1 (of the chamber) and 2 (of the disc) are

noted.

Now, the bad conductor is removed and the disc is heated by placing the chamber directly on the

disc. When the temperature of the disc is 2 + 100 (say ), the chamber is removed and disc is

allowed to cool. When the temperature of the disc is 2 + 50 , stop warch is started and the time

is noted in steps for every degree upto 2 - 50C. A graph is drawn between time

vs temperature and slope d/dt at 2 is found out.

MEASUREMENT OF THE RADIUS OF THE METALLIC DISC (r)

Z.E = ±----------- div

L.C = 0.01×102m Z.C = ± -----------div

S.No MSR VSC OBSERVED READING =

MSR+VSC(LC)

CORRECT

READING

= OR + ZC

Unit ×102m div ×10

-2m ×10

-2m

1

2

3

4

5

Mean Diameter ‘D’ = ---------×10-2

m

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TO FIND THE THICKNESS OF THE BAD CONDUCTOR (d)

Z.E = ±----------- div

L.C = 0.01×102m Z.C = ± -----------div

S.No PSR HSC OBSERVED READING =

PSR+HSC(LC)

CORRECT

READING

= OR + ZC

Unit ×103m Div ×10

-3m ×10

-3m

1

2

3

4

5

Mean thickness‘d’ = ---------×10-3

m

TO FIND THE THICKNESS OF THE METALLIC DISC (h)

S.No PSR HSC OBSERVED READING =

PSR+HSC(LC)

CORRECT

READING

= OR + ZC

Unit ×103m Div ×10

-3m ×10

-3m

1

2

3

4

5

Mean thickness‘d’ = ---------×10-3

m

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DETERMINATION OF THE RATE OF COOLING OF METALLIC DISC. { d dt }

Steady temperature in the metallic disc ( 2) = -----------------0C

TEMPERATURE TIME (t) TEMPERATURE( TIME(t)

0C Second

0C Second

Result

Thermal conductivity of the bad conductor = …………………………W m-1

K-1

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E 04 - AIR WEDGE

Aim: To determine the thickness of a thin wire by Air Wedge.

Apparatus Required:

Travelling microscope, Sodium vapor lamp, Two optically plane glass plate, Condensing lens,

Thin wire, Reading lens.

Formula:

Thickness of the thin wire T = L 2 m

= wavelength of the light.

L = Distance of the wire from the edge of contact

Mean width of one fringe

Procedure

The wire is introduced at one end between two optically plane glass plates. A parallel beam of

monochromatic light is incident on this at right angles. The rays of light reflected from the front

and back surfaces interfere and produce dark and bright fringes. The vertical cross-wire of the

travelling microscope is made to coincide with nth , n + 5th

, n + 10th

etc fringes and readings

are taken. From this , the fringe width , , is calculated.

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TO FIND THE FRINGE WIDTH: LC= 0.001 cm

Order of the

band

Microscope Readings Width of 5

bands

Mean Width

of one fringe

( ) MSR VSC TR =

MSR+(VSC×LC)

Unit ×102m Div ×10

2m ×10

2m ×10

2m

n

n+5

n+10

n+15

n+20

n+25

n+30

n+35

n+40

n+45

Mean fringe Width = --------×102m

To determine the distance between edge of contact and specimen wire

Position MSR VSC TR=MSR+(VSC+LC)

×102m Div ×10

2m

Rubber band

(edge of contact)

R1

Specimen wire R2

L = R1- R2 = ----------------------------×102m

Result :

Thickness of the given thin wire = ---------------- meter

KININDIA

E 05 - ULTRASONIC INTERFEROMETER

Aim: To determine the Ultrasonic velocity and compressibility of liquids.

Apparatus Required: Ultrasonic interferometer, Wave generator, Liquids.

Formula:

Wavelength of the Ultrasonic waves = d/n m

Velocity in liquid u = s frequency of crystal ms-1

Compressibility of the liquid = K = 1 / u2 m

2 N

-1

d = Distance moved by the reflector

n = Number of oscillations

ρ = Density of the liquid Kg / m3

Procedure:

The liquid is taken in the cell. This has a crystal transducer at the bottom and a metal reflector

attached to a micrometer screw is immersed. When the reflector is moved, the ammeter shows

maximum when the distance between the crystal and reflector is equal to whole multiplies by

sound due to the formation of standing waves.

The micrometer reading is noted for a particular maximum in the ammeter. Then readings are

noted for every five maxima. The difference in reading for two consecutive maxima gives

sound / 2. Thus sound is measured.

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TO FIND THE WAVELENGTH OF THE ULTRASONIC WAVES

Type of liquid = Water

Frequency of the generator (f) = 2 MHz (Constant value as per the experimenmtal set up )

Least Count (LC) = 0.01 mm

Total Readings (TR) = PSR + (HSC x LC)

S.No No.of

oscillation

(n)

Readings for ‘n’ oscillations Distance

moved by

reflector d

= R1-R2

Wave

length

d/n

Initial reading(R1) Initial reading(R2)

PSR HSC TR PSR HSC TR

×10-

3m

div ×10-

3m

×10-

3m

div ×10-

3m

×10-3

m ×10-3

m

1

2

3

4

5

Mean(m/s

Result :

Velocity of the Ultrasonic waves in the liquid = --------------------------- m/s

Compressibility of the given liquid = ----------------------- m2 N

-1

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