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I Year B.Tech (2018-2019)

Semester II

OBSERVATION NOTE BOOK

PHYSICS PRACTICALS

Name : ……………………………….

Section : ………………………………

Roll No :………………………………..

Branch : ………………………………..

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CONTENTS

S.No

Date Name of the Experiment Page No Signature of the

staff

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CONTENTS

S.No

Date Name of the Experiment Page No Signature of the

staff

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INDEX PAGE

I. MEASURING INSTRUMENTS

1. Spectrometer

II. LIST OF EXPERIMENTS

1. Determination of Coefficient of Viscosity of a given liquid by Poiseuille’s Method

2. Particle Size Determination using Laser source

3. Determination of Numerical Aperture of an Optical Fibre

4. Spectrometer – Refractive Index of the Material of the Prism

5. Potentiometer– Resistance of a Wire

6. Transistor Characteristics

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Diagram

Fig.a.Spectrometer

Fig .b. Spectrometer readings

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SPECTROMETER

Aim:

To study the functions of different parts of a spectrometer and their adjustments

Description:

The collimator is an arrangement for producing a parallel beam of light. It consists of a hollow

brass tune with a vertical slit (S), at one end and a Collimating Lens (L) at the other end. To

obtain parallel beam of rays, the distance between the slit and lens has to be adjusted. This can be

done by means of a side screw attached to the collimator. The width of the slit can be adjusted

by a screw attached to its side. The collimator is a fixed one and it cannot be rotated.

Telescope:

The telescope is attached to a circular scale graduated in degrees. It can be rotated about a

circular axis passing through the centre of the circular scale. It has an objective O near the

collimator ad an eye piece E at the other end. The eye piece of the telescope is provided with

crosswire. The focusing of the telescope is done by a screw attached to the side of the telescope.

The telescope can be rotated and fixed at any position using a ain screw. The telescope can be

rotated by very small amounts by a fine adjustments screw which is tangential to the main screw.

Prism table

The prism table consists of two identical metal discs separated by three springs. Through the

springs pass three levelling screws. The top surface of the upper disc contains lines to mount the

prism in proper position. The prisms table can be raised or lowered and fixed at an desired height

by means of a screw. The prism table can be rotated about the same vertical axis as the telescope.

A vernier disc attached to vertical axis carries two diametrically opposite vernier scales VA and

VB . The vernier disc can be rotated and fixed at any position by a main screw and a fine screw as

in the telescope.

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LC = 1’

Vernier A Vernier B

MSR

deg

VSC

div

VSR =

VSCXLC

deg

TR= MSR

+ VSR

deg

MSR

deg

VSC

div

VSR =

VSCXLC

deg

TR= MSR

+ VSR

deg

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Procedure

Initial adjustments:

Eye piece: The telescope is turned towards a white wall and the eye piece alone is adjusted until

the cross wires are clearly seen.

Telescope: The telescope is turned towards a distant object. The distance between the eyepiece

and objective is adjusted by the screw until a clear image is seen on the crosswire.

Collimator: The slit of collimator is illuminated by sodium light. The slit is adjusted fine and

narrow. The distance between the slit and the collimating lens is adjusted so that clear image is

got on the cross wire when the telescope is brought in line with the collimator.

Prism table: The prism table is made horizontal using a spirit level. The spirit level is placed on

the prism table along the line joining any two legs. Then the leveling screws of the prism table

alone are adjusted until the air bubble comes to the centre. The process is repeated by keeping

the spirit level at different places until the prism table is exactly horizontal.

To find least count:The value of each main scale division is half degree(=30). The number of

vernier scale divisions is 30.29 main scale divisions are divided into 30 vernier scale divisions(ie

30VSD = 29MSD). Therefore value of 1 VSD= 29/30 MSD. It is known that the least count is

the difference between 1 MSD and 1VSD.

Least count(LC) = 1MSD – 1VSD

= 1MSD – 29/30 MSD

= 1/30 MSD = 1/30 x 30’ =1’

Least count = 1’ (one minute)

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To read the readings

During experimentation readings must be taken from both vernier A and vernier B scales and

tabulated. Fig. b shows the typical reading observed in vernier A and vernier B. since vernier A

and vernier B are at diametrically opposite places in the circular vernier disc, in a perfect

instrument the difference between these readings must be 1800.

Result

The difference in vernier scale readings are found to be …………..

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DIAGRAM

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1.POISEUILLE’S METHOD

Expt No : Date :

AIM:

To determine the coefficient of viscosity of the given liquid by Poiseiulle’s method.

APPARATUS REQUIRED:

A graduated burette, rubber tube, capillary tube, pinch cork,stop watch etc.

FORMULA :

Coefficient of viscosity ot the given liquid = =

V

ht

l

gr

8

4

Nsm-2

EXPLANATION OF SYMBOLS:

Symbol Explanation Unit

Density of the given liquid kg /m3

g Acceleration due to gravity m/s2

r Radius of the capillary tube meter

l Length of the capillary tube meter

h Driving height of the liquid level meter

t Time taken for a known height of liquid to flow Seconds

V Volume of the liquid m3

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TABULAR COLUMN:

TABLE 1 : Tofind (ht/V)

S. No

ho = ---

------ x

10-2

m

S. No

Range

(Burette)

Reading)

Volume x 10-6

m3

Time of

flow(sec)

(sec)

h1 x

10-2

m

h2 x

10-2

m

h =[

h0

10-2

m

ht/Vx 104

sec/m2

sec/ m2 0 –5

5 – 10

10 – 15

15 – 20

20 – 25

25 – 30

30 – 35

35 – 40

40 – 45

45 – 50

CALCULATIONS

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PROCEDURE:

The burette is filled with the given liquid. A capillary tube is attached to the lower end of

the burette using a rubber tube. The capillary tube is made vertical and the liquid is allowed to

flow through it. When the liquid comes to a known height (h1), height measured from the axis of

the capillary tube, the stopwatch is started. The stopwatch is stopped when the liquid flows to

another level (h2). The driving height is given by h = ((h1 + h2) / 2) – h0, where h0 is the height of

the center of the capillary tube from table. (Since h1 and h2 are measured from table and driving

height is with respect to the capillary tube, the term h0 is incorporated in the formula for driving

height.) The volume of the liquid and time of flow are noted. Using the above formula the

coefficient of viscosity of the given liquid can be calculated. The radius of the capillary tube will

be given.

RESULT

The coefficient of viscosity of the given liquid is = ------------------------Nsm-2

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DIAGRAM

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Expt No : Date :

2. PARTICLE SIZE DETERMINATION USING LASER SOURCE

AIM:

To determine the particle size of the given lycopodium powder using laser diffraction method.

APPARATUS REQUIRED:

He-Ne laser or semiconductor laser, Lycopodium powder, Glass plate, Screen.

FORMULAS USED:

Grain size (diameter) ‘2d’ of the given particle

2d =

metre

EXPLANATION OF SYMBOLS:

Symbol Explanation Unit

D Distance between the screen and glass plate metres

Wavelength of Helium-Neon laser metres

xn Distance between the central bright point and n

th fringe (xn) metres

n Order of rings -

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TABULAR COLUMN:

Sl.No Distance between

the screen and the

glass plate D (cm)

Order of

Diffraction

n.

Distance between the

central bright point and

nth

fringe (xn) (cm)

Particle size

2d =

cm

1 1

2

3

4

2 1

2

3

4

Mean = ..............x10-2

m

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PROCEDURE:

The powder of few microns whose size is to be determined is spread over the glass plate. The

glass plate is inserted vertically through the path of the laser beam.To get the contrast circular

rings on the screen the glass plate is adjusted until clear image is formed. After the ring

formation using white paper or trace sheet the circular patterns are marked carefully. The ratio of

different order dark rings(xn) are measured. The distance between the screen and the glass plate

D is measured. Knowing all, the size of particle can be calculated. Using the formula the particle

size can be found for different D value.

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CALCULATIONS:

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RESULT:

Particle size of the given lycopodium powder = ................10-2

m

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DIAGRAM

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Expt No : Date :

3. NUMERICAL APERTURE OF AN OPTICAL FIBRE

AIM

To determine the acceptance angle and numerical aperture of the given fibre optic cable.

APPARATUS REQUIRED

Diode laser source, fibre optic cable (typically 1 m ) and NA plate

FORMULA

1.Numerical Aperture of the given optical fibre

𝑵𝑨= 𝒔𝒊 𝜽𝒎𝒂

𝑵𝑨 = /(𝟒𝑳2+ 𝟐)𝟏

/𝟐

𝟐.Acceptance angle of the given optical fibre 𝜽𝒎𝒂 = 𝐬𝐢𝐧−1(𝐍𝐀)

Where θ max is the acceptance angle of the fibre

Symbol Explanation Unit

D Diameter of the laser spot noted on the screen in meter

metres

L Distance of the screen from the fibre end

metres

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TABULAR COLUMN

Measurement of Numerical Aperture

S.No Distance of the spot

from fibre end (L) in

10-3

m

Diameter of spot(D) in 10

-3m

NA = D/(4𝐿2+𝐷2

)1/2 θ max = sin

-1 (NA)

OBSERVATIONS

Distance of the spot from the fibre end(L) = 10-3

m

Diameter of the spot = 10-3

m

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PROCEDURE :

Numerical aperture of any optical system is a measure of how much light can be

collected by the optical system. It is the product of the refractive index of the incident medium

and the sine of the maximum ray angle. The schematic diagram of the numerical aperture

measurement system is shown in the figure.

One end of the 1 metre optical fibre cable is connected to PO of source and the other end

to the NA JIG as shown in the figure. The AC main is switched on. Light should appear at the

end of the fibre on the NA JIG. Turn the set Po knob clockwise to set to maximum intensity.

The white screen in the NA JIG with the 4 concentric circles each of 10, 15 20, and 25

mm in diameter is kept vertically at a suitable distance so that the red spot from the emitting fibre

coincides with the smallest (10mm) circle. The circumference of the spot outermost must

coincide with the circle. A dark room will facilitate good contrast. The distance of the screen

from the fibre end L and the diameter of the spot are noted. The diameter of the circle is

measured accurately with a suitable scale which is provided in the JIG itself. The experiment is

repeated for 15 min, 20 mm, and 25 mm diameters in the same way. The readings are tabulated.

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CALCULATIONS

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RESULT:

1. Numerical aperture of the given fibre optic cable =

2. Acceptance angle of the fibre =

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DIAGRAM

Angle of Prism Angle of minimum deviation

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4.SPECTROMETER – REFRACTIVE INDEX OF THE MATERIAL OF THE PRISM

Expt No : Date :

AIM:

To determine the refractive index of the material of the prism

APPARATUS REQUIRED:

A monochromatic source, prism, reading lens etc.,

FORMULA :

Refractive index of the material of the prism

μ =

2sin

2sin

A

DA

(no unit)

EXPLANATION OF SYMBOLS:

Symbol Explanation Unit

A Angle of the prism degrees.

D Angle of minimum deviation degrees

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TABULAR COLUMN:

To Find Angle of Minimum Deviation

Position Vernier A Vernier B

MSR

deg

VSC

div

VSR =

VSC x LC

deg

Deg

TR

deg

MSR

deg

VSC

Div

VSR =

VSC x LC

deg

TR

deg

Deviated

Ray

Direct Ray

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PROCEDURE:

The initial adjustments of the spectrometer are made. The prism is placed on the prism table and

is illuminated by a sodium vapour lamp. The prism is placed in such a way that its base is

parallel to the collimator. The deviated ray is found by moving the telescope towards the base of

the prism and the prism table is rotated such that the slit moves in a particular direction (ie

towards the direct ray), stops and retraces its path. This position is found out and the slit is made

to coincide with the cross wire and readings are noted, from which angle of deviation is

determined. Assuming the value of the angle of Prism (A = 60ο), the value of the refractive index

of the material of the prism is found out.

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CALCULATIONS

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RESULT: .

The refractive index of the material of the prism = -----------

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CIRCUIT DIAGRAM

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5.POTENTIOMETER-RESISTANCE OF A WIRE

Expt No : Date :

AIM:

To determine the resistance of a wire using potentiometer.

APPARATUS REQUIRED:

Accumulator, Six volt battery, Resistance wire, Rheostat, High resistance,

Galvanometer, Double pole double throw key (DPDT key), Resistance box, Plug

key.

FORMULA

Resistance of the given wire X = R(l2/l1) ohm

Symbol Explanation Unit

l1 Balancing length for R meter

l2 Balancing length for X meter

R Value of resistance in box ohm

X Resistance of the given wire ohm

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OBSERVATIONS

Resistance in box R = ………. Ohm

Balancing length for R , l1 = ……..x10-2

m

Balancing length for X , l2 = …….x10-2

m

TABULAR COLUMN

S.No R

(ohm)

for X

cm

for R

cm

X = R(l2/l1)

ohm

Mean X = ohm

CALCULATIONS:

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PROCEDURE:

The primary circuit consists of an accumulator Acc1 is connected across the two ends of the

potentiometer wire AB. The second accumulator Acc2 is connected in the secondary circuit. The

DPDT switch is connected to the jockey through high resistance and galvanometer. The proper

polarity of the terminals must be ensured that the top row terminals are positive and bottom row

terminals are negative. The rheostat is adjusted to get opposite side deflections in galvanometer.

When the jockey is in contact at two extreme ends of the potentiometer wire .The DPDT switch

is thrown to one side so that the resistance R is included in the circuit and the balancing length

l1is measured. The switch is thrown in the opposite direction so that the coil X is included and

the balancing length l2 is measured. In each value of R, the rheostat should be adjusted to get

opposite deflections both for potential drops across R and X respectively.

RESULT: .

Resistance of the given wire = ….…ohm

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6. TRANSISTOR CHARACTERISTICS

Expt No : Date :

AIM:

To study the Common Base characteristics for the given transistor.

APPARATUS REQUIRED

Bread Board, Transistor, ammeter (milli ammeter and micro ammeter), voltmeter

FORMULA:

Input Resisitance Ri = CE

VB

BE

dI

dV

Ω

Output Resistance Ro = B

IC

CE

dI

dV

Ω

Current Gain β = CE

VB

C

dI

dI

No Unit

EXPLANATION OF SYMBOLS:

Symbol Explanation Unit

dVBE Small change in base emitter voltage Volt

dVCE small change in collector emitter voltage Volt

dIB small change in base (Input) Current Ampere

dIC Small Change in Collector (Output) Current Ampere

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TABULAR COLUMN

INPUT CHARACTERISTICS

S.No VCE(v) = VCE(v) =

VBE(v) IB(μA) VBE(v) IB(μA)

OUTPUT CHARACTERISTICS

S.No IB (μA) = IB (μA) =

VCE (V) IC (mA) VCE (V) IC (mA)

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PROCEDURE:

Electrical Connections are made as shown in the figure.

To study the input characteristics, collector emitter voltage is kept constant and the

variation of base current (IB)with respect to input voltage (VBE) is noted. The procedure is

repeated for different values of VCE.

To obtain output characteristics, the changes in collector current (IC) with respect to

collector emitter voltage (VCE) for various values of base current (IB) are measured.

To determine the gain (β) of the transistor VCE should be kept constant and IB is varied and

corresponding collector current (IC) is noted.

With all these, graphs for input, output and gain characteristics are drawn.

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GAIN

S.No VCE = v

IB (μA) IC (mA)

CALCULATIONS

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RESULT:

The transistor characteristics in common emitter configuration were drawn and studied.

Input Resistance = ------------------

Output Resistance = -----------------

Current gain = -------------------

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