GUDLAVALLERU ENGINEERING COLLEGESESHADRI RAO KNOWLEDGE VILLAGE

GUDLAVALLERU

Department of

BASIC SCIENCES

NAME :…………………………………………………………

ROLL NO.: ……………………………………………………

BRANCH: ………………… SECTION:…………………….

YEAR & SEMESTER: ………………………………………

NAME OF THE LAB: ……………………………………….

LAB MANUAL

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Engineering PhysicsLab Manual

By

S.SURESHDepartment of Science & Humanities

Gudlavalleru Engineering College,Gudlavalleru.

Common to CE,EEE,ME,ECE,CSE & IT

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Instructions for Laboratory

The objective of the laboratory is learning. The experiments are designed to illustrate

phenomena in different areas of Physics and to expose you to measuring instruments.

Conduct the experiments with interest and an attitude of learning.

You need to come well prepared for the experiment

Work quietly and carefully (the whole purpose of experimentation is to make reliable

measurements!) and equally share the work with your partners.

Be honest in recording and representing your data. Never make up readings or doctor

them to get a better fit for a graph. If a particular reading appears wrong repeat the

measurement carefully. In any event all the data recorded in the tables have to be

faithfully displayed on the graph.

All presentations of data, tables and graphs calculations should be neatly and carefully

done.

Bring necessary graph papers for each of experiment. Learn to optimize on usage of

graph papers.

Graphs should be neatly drawn with pencil. Always label graphs and the axes and

display units.

If you finish early, spend the remaining time to complete the calculations and drawing

graphs. Come equipped with calculator, scales, pencils etc.

Do not fiddle idly with apparatus. Handle instruments with care. Report any breakage

to the Instructor. Return all the equipment you have signed out for the purpose of your

experiment.

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INDEXS.No Name of the experiment Date Marks Signature

1 TORSIONAL PENDULUM.

2 MELDE’S EXPERIMENT.

3 REFRACTIVE INDEX OFMATERIAL OF THE PRISM

4 DIFFRACTION GRATING

5 NEWTON’S RINGS

6 PARALLEL FRINGES

7 VOLUME RESONATOR

8 TIME CONSTANT OF RCCIRCUIT

9 RESONANCE IN LCR CIRCUIT

10 MAGNETIC FIELD ALONG THEAXIS OF A COIL (STEWART &GEES METHOD)

11 ENERGY GAP OF A MATERIALOF P-N JUNCTION

12 ZENAR DIODE

Note: You have to perform minimum ten experiments

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Wall Bracket

l

Sl.no Length ofthe wire( l)betweentwochucks(cm)

Time taken for 20oscillations(sec)= t

Timeperiod(sec)

T=

T2 l/T2

Trial I Trial II Mean

S.No Main Scale Reading (a) VernierCoincidence (n)

b = n X L.C Total Reading

(a+b) cm

S.No Pitch Scale

Reading (a)

Head ScaleReading (n1)

Corrected HeadScale Reading n = n1

Correction

b = nXL.C Total Reading

(a+b) mm

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ENGINEERING PHYSICS LAB RECORD

S.SURESH

TORSIONAL PENDULUM

Aim:

To determine the rigidity modulus ( ) of the material of the given wire using torsionpendulum.

Apparatus:

Torsional pendulum, stop watch, meter scale, screw gauge, vernier calipers.

Procedure:

Torsional pendulum consists of a uniform circular metal disc of diameter about 12cmand thickness of 2cm suspended by a metal wire at the center of disc.

The other end is gripped into another chuck nut which is fixed to wall bracket.

The length (l ) of the wire between two chucks can be adjusted and measured by a meterscale.

An ink mark is made on the curved edge of the disc.

The disc is set into oscillations in the horizontal plane, by turning through a small angle(300). Now stop watch is started and time (t) for 20 oscillations is noted. This procedure isrepeated for two times and the average value is taken. The time periodT(= ) is calculated. The experiment is performed for three different lengths of the wire andobservations are tabulated.

The diameter and hence the radius(a) of the wire is determined accurately at least threedifferent places of the wire using screw gauge, since the radius of the wire is small inmagnitude and appears with fourth power in the formula of rigidity modulus.

The mass (M) and the radius (R) of the circular disc are measured by using roughbalance and vernier calipers respectively.

A plot is drawn between l on x-axis and T2 on y- axis, which is a straight line passing throughthe origin. The inverse of the slope of the graph gives the average value of l/T2. Rigiditymodulus ( ) of the given wire is determined by using

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l

T2

Model graph

2

4 2

4 MR l

a T

Dyne/cm2

CALCULATIONS:

Result: the rigidity modulus of given wire is from experiment and

From graph

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( )

Transverse Mode

( )

Longitudinal Mode

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Melde’s ExperimentAim:

To determine the frequency of the electrically driven tuning fork

Apparatus:

Electrically maintained tuning fork, a light card pan, frictionless pulley, a box ofweights, sewing thread.

Principle:

Transverse mode: In this mode tuning fork is arranged in such a way that the prongs vibratein a direction perpendicular to the length of the string Transverse Stationary waves are setup in the thread when the frequency of the tuning fork is equal to the frequency of thevibrating string. The frequency (n) of the tuning fork is given by the formula.

1

2

Tn

l m

Where l = loop length i.e. the distance between any two successive nodes in cm

T = Tension applied to the string in dyne

m = Linear density (mass per unit length) of the string in gm per cm.

Longitudinal mode: In this mode tuning fork is fixed so that the prongs vibrate in a directionparallel to the length of the string. Longitudinal stationery waves are in the string, when thefrequency of the tuning fork is equal to twice the frequency of the string. Therefore thefrequency (n) of the fork is given by

1 Tn

l m

With the same tension and for a given length of the wire the loop length in the longitudinalarrangement will be doubles that in the transverse arrangement.

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Transverse mode

S.No Load in thepan (M)=gm

Load in thepan + panweight(M+m)

T = (M+m)g

Dynes

Length ofthe loop(l)

√

CALCULATIONS:

Longitudinal mode

S.No Load in thepan (M)=gm

Load in thepan + panweight(M+m)

T=(M+m)g

Dynes

Length ofthe loop(l)

=cms

√

CALCULATIONS:

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PROCEDURE:

A sewing thread is connected to one of the prongs of an electrically maintainedtuning fork. The other end of the thread is passed over a frictionless pulley P and tied to acard board pan C of known weight. The pulley is fixed to a separate stand so that thedistance between the pulley and the tuning fork may be altered.

1. The fork is set up so that the string vibrates transversely. A suitable load is placed inthe card board pan. The tuning fork is excited by closing the electrical circuit. Thelength of the string is altered by moving the pulley till well defined steady stationarywaves are formed along the string. By means of a meter scale the average looplength l is measured. Since linear density m is a very small quantity it is determinedby weighing 4 or 5 m length of the string. The sum of weights of the pan and theload placed in it gives the tension. The frequency of the tuning fork is calculatedfrom expression.

2. The tuning fork is next arranged so that the string vibrated longitudinally. The aboveprocess is repeated and the loop lengths are determined using the same load as in(1). The frequency of the tuning fork is calculated by using the expression (2). Theresults are tabulated.

Result : the frequency of the tuning fork in transverse mode is _______Hzand longitudinal mode is ________Hz.

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Colour ofthe line

Position of minimumdeviation

Direct reading Angle of minimumdeviation =D

µ

Verniar I Verniar II Verniar I Verniar II Verniar I Verniar II

BLUE

RED

D

Collimator

TelescopeT2

T1

P

Q

S

A

B

C

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Dispersive power of material of the prism

AIM:

To determine the refractive index of the material of the prism

APPARATUS:

Spectrometer, Mercury Vapour lamp, flint glass prism, magnifying glass

THEORY:

The refractive index of the material of the prism can be determined by the methodof minimum deviation and using the formula.

( )sin

2

sin2

A D

A

Where A = Angle of equilateral prism = 60o

D = Angle of minimum deviation

Description of the Spectrometer:

The spectrometer is an instrument for the production of spectra and is provided withnecessary adjustments for the measurement of deviations. It consists essentially of threemain parts.

(1) Collimator : The collimator serves to provide a parallel beam of light from thesource. It comprises a tube with an achromatic lens at one end and an adjustable slit at theother.

(2) Prism: A suitable prism is required to disperse the light and is mounted on arevolving table above the main table of the spectrometer.

(3) Telescope: the function of the telescope is to receive the dispersed rays and is providedwith a Ramsden eyepiece fitted with cross wires for the measurement of deviation.

The optic axes of collimator and telescope intersect on the common axis of rotation axis ofrotation of the prism and telescope. But before the use, certain adjustments have to bemade as under.

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Adjustments:

(1) Cross wires: The eyepiece of the telescope is adjusted until the cross wires areseen distinctly.

(2) Telescope : The telescope is directed towards a distant object and is adjusted bymeans of the focusing screw until there is no parallax between the image of the distantobject and the cross wires

(3) Collimator:Having set the telescope to receive parallel light it is now turned to receivelight from the collimator illuminated by the sodium lamp. The position of the slit is adjusteduntil image is clearly seen in the telescope. The Collimator now gives parallel light.

Prism: The prism is placed with its refracting edge towards the collimator, and the telescopeis moved round to receive an image of the slit reflected from one face. The telescope is nowfixed and the leveling screw of the prism table are adjusted, so that, the image is in thecentre of the telescope’s field. The prism table is rotated until the image from the secondface is received by the telescope.

Procedure:

Preliminary adjustment of the spectrometer is made. The slit of the collimators illuminatedwith mercury vapour lamp. The prism is placed on the prism table, as in Fig. such that lightenters the prism from one face and emerges from the other. The telescope is turnedtowards the emerging beam to see the refracted image.

The prism table is turned and the direction in which the angle of deviation decreases isnoted. The prism table is slowly rotated in that direction following the image through thetelescope by moving it also in the same direction until the image becomes steady for a whileat a certain stage and begins to retrace its path on further rotation of the prism table. Now,the prism table is fixed and the image is made to coincide with the centre of the cross wires,the readings of both the verniers are noted. Removing the prism without disturbing theprism table the telescope is turned to receive the direct image of the slit and the twoverniers are read after the coincidence is made. The mean difference between the tworeadings gives the angle of minimum deviation of the prism.

The experiment is performed for two colours – Blue & Red of the spectrum in order to findthe dispersive power of the prism. The refractive index and dispersive power of thematerial of the prism are calculated using the equations. The results are tabulated in table.

Result:

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Order ofthe

spectrum

line Reading on thecircular scale

when thetelescope is onthe right hand

side

Reading on thecircular scale

when thetelescope is onleft hand side

Directreading

Difference sinθ

VerniarI

VerniarII

VerniarI

VerniarII

00

or

1800

or

3600

θ1 θ2 meanθ

Firstorder

D1

D2

Secondorder

D1

D2

Currentautoassociativenetworks

T

N

450

C

T

T0T1

T1

T2

T0

900

T2

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Diffraction Grating

Diffraction Grating Normal Incidence

AIM:

To determine wave length of the yellow 1 and yellow2 lines by using diffractiongrating by the method of normal incidence.

APPARATUS:

Spectrometer, Diffraction grating, Mercury lamp, magnifying glass.

Normal Incidence Method:

Preliminary adjustments of the spectrometer are made. The grating table is leveled using aspirit level. The grating is mounted on the grating table for the normal incidence. The slit ofthe collimator is illuminated with sodium light.

The experiment is performed in the following steps.

1. The collimator (c) is adjusted with a fine slit for sending parallel rays. The welldefined image of the slit is observed through the telescope (T).

2. Two verniers are adjusted such that their zeros coincide with the zero and 180o ofthe main scale.

3. The least count and the direct reading (Ro) are noted.4. The telescope (T) is rotated through 90oexactly from Ro and then fixed.5. Now, the grating G is mounted on the grating table and adjusted until the ray from C

is incident on it at 45o. The reflected ray will be observed in T.6. Without disturbing T, Vernier scale alone is released and is turned along with the

grating table and G through 45oexactly.7. Now, the vernier scale and main scale are fixed at T is brought back to To position.

Now, the ray from C is said to be normally incident on G.8. When telescope is at To the readings from the verniers V1&V2should correspond to

Ro.9. T is moved to left to observe first order diffraction pattern. The point of intersection

of the cross wires is coincided with it. This position of telescope is T1. The readingsof V1 and V2are noted. Similarly, the readings for second order are noted, when thetelescope is at T2position.

10. The Step 9 is repeated when telescope is at right side of T0and readings at T1andT2positions are noted. The results are tabulated in table.

sin

nN

where n = order of the spectrum, N = grating element = wavelength.

result:

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S.NO FRINGENO

(LEFT)

MICROSCOPE

READING(A)

FRINGE NO

(RIGHT)

MICROSCOPE

READING(B)

D=A-B D2

1 20 20

2 15 15

3 10 10

4 5 5

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Newton’s rings

AIM: To determine the Radius of curvature of given Plano convex lens by the method ofNewton’s rings.

Apparatus:

Travelling microscope, Sodium vapour lamp, Plano-convex lens of about 100 cm focallength, a thick glass plate, a magnifying glass, a black paper.

PRINCIPLE:

Optical interference due to the air wedge formed by the circular lens.

The Radius of curvature of given Plano convex lens can be determined by using the formula= ( )( )Where D1 = Diameter of n1 ring. D2 = Diameter of n2 ring.

R = Radius of curvature of the surfaces of the lens in contact with theglass plate.

PROCEDURE:

The apparatus is arranged as in fig. first the surfaces of the Plano convex lens and the glassplates (P1& P2) are thoroughly cleaned. A black paper is placed on the base of the travelingmicroscope over which the thick glass plate (P1) is placed. Over the thick glass plate (P1) aPlano convex lens (L1) is placed such that the convex surface of the lens touches the glassplate. By keeping the short focus lens or converging lens (LO2) at a distance equal to itsfocal length from the sodium lamp(s) a parallel beam of light is obtained which is directedon to apparatus by the thin glass plate (P2) at an angle of 45oto the horizontal and theinterference fringes are observed in the microscope (M0). The microscope is adjusted untilthe fringes are sharply in focus and the definition of the fringes in increased by slightadjustments to the reflecting plate (P2) and sodium vapour lamp. Having centered the crosswires on the centre of the fringe system, the microscope is then moved across the field andreadings of the vernier are taken with cross wires focused on the successive dark fringes,beginning say at the 20th fringe on the left, and ending on the 20the fringe on the right.

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Readings are with the microscope moving in one direction to avoid errors due to backlash.Radius of curvature of the lens is determined using a sphere meter. Readings are tabulatedin Table.

S.NO FRINGENO MICROSCOPE

READING(A)

FRINGENO MICROSCOPE

READING(B)

C=A-B =C/5

1 0 5

2 10 15

3 20 25

THIN OBJECT

PLANE GLASS PLATES

PARALLEL FRINGES

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Parallel fringes

AIM:

To determine diameter or thickness of a thin wire by optical interference method.

APPARATUS:

Thin wire, two optically plane glass plates of dimensions 1” x 3”, travelingmicroscope, sodium lamp, reflecting glass plates, magnifying glass.

THEORY : In case of a thin air film of thickness ‘t’ , path difference between the tworeflected rays from the wedge system is 2tcosr = n . If incident ray is close to the normal,i= and r=0. So 2t = n …..(1)If ‘L’ is the length of the wedge, ‘n’ is the number of fringes and

is the finge width , then n =L …….(2). Substituting (2) in (1) 2

L

t So

2

Lt .

PROCEDURE:

A thin wedge of air film forms when a thin wire is placed at one end in between twooptically plane glass plates and the other end of the plates being in contact with oneanother, as shown in figure. The reflecting glass plate is arranged in such a way that thelight from the source is reflected on to the combination of the glass plates. The wedgemakes a small angle. When the air film is illuminated by the monochromatic light, alternatedark and bright fringes are observed through the microscope (M) which are parallel to theline of intersection of two slides.

The eye piece of the microscope is adjusted so that the fringes are clearly seen. Themicroscope is moved to one end of the glass plate until the cross wire coincides with one ofthe fringes, say nthfringe. The microscope reading is noted. The microscope is now movedto the same direction and the reading is noted each time at (n+4); (n+6) ………… (n+20)thfringe. The observations are tabulated in table.

The thickness of the wire is calculated by substituting the values of β, λ and L in the formula.

RESULT:

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Sl.No. Frequency of thetuning fork (n) Hz

Resonating Volume of air Velocity of sound

V= 2πnA

vL cm/seTrial-1 Trial-2 Mean ‘v’ Cm3

1

3

4

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VOLUME RESONATOR

Aim: Determination of velocity of sound in air at room temperature using VolumeResonator.

Apparatus: Aspirator bottle, beaker, measuring jar, tuning forks, vernier calipers, rubberhammer, meter scale.

Description: The volume resonator consists of an aspirator bottle filled with water having asmall neck and some outlet (opening) at itsbottom. A bottle from which water is drawnthrough a narrow tube is called an aspirator bottle. The outlet is fitted with a one-holedrubber stopper into which a short glass tube is inserted. A rubber tube with a pinch cock isconnected to the glass tube. Water can be drawn from the bottle into a measuring jar byopening pinch cock

THEORY : Excited tuning fork kept at the neck of the bottle vibrates forcibly air columnpresent above the surface of water. Water run down slowly is collected into a measuringjar. Longitudinal stationary waves are formed in air. As water is run down, at someinstance, a booming sound is produced due to resonance. Here frequency of vibrating aircolumn becomes equal to the frequency of the tuning fork.

PRINCIPLE: It works on the principle of resonance. When air column vibrates with naturalfrequency of tuning fork, loud sound is heard due to increase in amplitude.

PROCEDURE: The bottle is completely filled with water. A tuning fork of known frequency‘n’ is excited and kept just above the neck of the bottle. Water in the bottle is slowly rundown and collected in the measuring jar by opening the pinch cock. When volume of airinside the bottle reaches a particular value, loud sound is heard due to resonance. Thenpinch cock is closed and volume ‘v’ of water collected is measured directly by the jar. It is infact equal to the volume of air present in the bottle. 3 more such readings are taken withdifferent tuning forks and values are noted in the table. Length of the neck of the bottle ismeasured with a scale and its radius ‘r’ is measured by vernier calipers.

OBSERVATIONS: Length of the neck of the bottle L= cm

Area of the neck of the bottle A = π r2 = cm2

Formula: Velocity of sound in air at room temperature is V= 2πn2

)(

r

LeV

cm/sec

Calculations:

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R

C V

SPDT

V= 2πn2

)(

r

LeV

cm/sec

= cm/sec

RESULT: Velocity of sound in air at room temperature is found to be cm/sec.

S.No. time (t) Secs Charging

voltage

Discharging

voltage1 0

2 10

3 20

4 30

5 40

6 50

7 60

8 70

9 80

10 90

11 95

12 100

13 105

14 110

15 115

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Time Constant of RC Circuit

AIM: To determine the time constant ‘ ’ of the circuit by charging and discharging

APPARATUS: D.C.Voltage source, resistors, a capacitor, digital micro ammeter, Charge anddischarge key.

PROCEDURE: . If switch spdt is closed then the battery charges the capacitor and current

flows through the resistor R until the capacitor is fully charged. If the charge on the capacitor

at time t is q(t) , then the voltage across the capacitor C is q/C and the current through R is i

= dq/dt . By

applying Kirchhoff’s second law.

iR1 + (q/C) = ε R1(dq/dt) + (q/C) = ε …………..(1)

16 120

17 125

18 130

19 135

20 140

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which has the solution

1 1/ /0

0

( ) (1 ) (1 )t R C t R Cq t C e q e

Where q C

…………………..(2)

The quantity = RC is the charging time constant which characterizes the rate at which

charge is deposited on the capacitor .As t∞, eq (2) shows that q Cε = q0. In Practice the

Capacitor charges to its maximum value q0 after a time interval equal to a few time constants.

Once the capacitor is fully charged then the current i through the resistor become zero.

At this point if the switch spdt short circuited it discharges through the resistor R

By Kirchoff’s second law

2

2

0

/0

( ) ( ) 0

( 0)

( ) t R C

dq qR

dt cwith solution taking q q at t

q t q e

Thus the charge on the capacitor decays exponentially with time. In fact after a time

t=RC (equal to the discharging time constant) the charge drops from it’s initial value q0 by a

factor of e-1.

GRAPH:

Plot a graph time in seconds on the x-axis and current in A on y-axis and find the

time for a fall to 0.37 × I max. Let this be =RESULT: R = ________________________ C = ________________________

The time constant in charging mode is :

The

time

constant in discharging mode is:

The time constant from graph is :

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Part A: Series LCR Circuit. Part B: Parallel LCR Circuit.

L = ___________ mH C ___________ µF.

.No. currentFrequency

() Hz

S.No. current

1 500 Frequency

() Hz2 1000 1 5003 1500 2 10004 2000 3 15005 2500 4 20006 3000 5 25007 4000 6 30008 4500 7 40009 5000 8 450010 5500 9 500011 6000 10 550012 6500 11 600013 7000 12 650014 7500 13 700015 8000 14 750016 8500 15 800017 9000 16 850018 9500 17 900019 10000 18 950020 10500 19 10000

20 10500

Resonance in LCR circuit

Aim: To study resonance effect inseries and parallel LCR circuit

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Apparatus: A signal generator, inductor, capacitor, ammeter, resistors, AC milli voltmeter.

Basic methodology:In the series LCR circuit, an inductor (L), capacitor (C) and resistance(R) are connected in

series with a variable frequency sinusoidal emf source and the voltage across the resistance is

measured. As the frequency is varied, the current in the circuit (and hence the voltage across R)

becomes maximum at the resonance frequency1

2rf

LC . In the parallel LCR circuit there is a

minimum of the current at the resonance frequency.

Power Resonance:The power dissipated at the resistor is P = I V = I2R = V2R

The average power dissipated over one cycle is20

2

I Rp

Fig 4 shows graph of p as a function of the driving frequency rf .

The maximum power value mP occurs at the resonating frequency

1

2rf

LC

It can be shown that to a good approximation, which the power falls to half of the maximum

value, mP /2 at2rf f

. Here is related to damping in the electrical circuit and is given by

= R/L. The width or range of f over which the value of p falls to half the maximum at

the resonance is called the Full Width Half Maximum (FWHM). The FHWM is a

characteristic of the power resonance curve and is related to the amount of damping in the

system. Clearly FWHM = = R/L. One also defines the quality factor Q as1rf L

QR C

which is also measure damping. Large Q (small R) implies small damping while small Q

(large R) implies large damping. Clearly we have FWHM = = R/L. Thus, the quality factor

Q can be determined from the FWHM of the power resonance graph.

Procedure:

1. The series and parallel LCR circuits are to be connected as shown in fig 1 & fig 2.

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2. Set the inductance of the variable inductance value and the capacitances the variable

capacitor to low values ( L ~ 0.01H , C ~ 0.1 µ F ) so that the resonant frequency

1

2rf

LC is of order of a few kHz .

3. Choose the scale of the AC milli voltmeter so that the expected resonance occurs at

approximately the middle of the scale.

4. Vary the frequency of the oscillator and record the voltage across the resistor.

5. Repeat (for both series and parallel LCR circuits) fir three values of the resistor (say R =

100, 200 & 300 ).

Calculations and Results:

1. Plot the graph of frequency ( ) vs I (current) for series and parallel cases.

2. Read off the resonant frequency1

2rf

LC by locating the maxima / minima in the

graphs

i). Resonance frequency for series LCR circuit =________________kHz

ii) Resonance frequency for parallel LCR circuit =________________kHz

iii). Calculate the value of resonance frequency =________________kHz

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Distance

d(cm)

Deflection in the magnetometer East side θE

(degree)

Mean

θE

Tan

θE

Deflection in the magnetometer West side θW

(degree)

Mean

θW

tanθW

θ1 θ2 θ3 θ4 θ1 θ2 θ3 θ4

Distanced(cm)

MeanθE

meanθW

(deg) Tanθ

Magnetic Induction ,B

Theoretical Experimental

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STEWART AND GEE’S EXPERIMENT.

Aim: To determine magnetic induction at several points on the axis of a circular coilcarrying current using Stewart and Gee’s type of tangent galvanometer.

Apparatus: Stewart and Gee’s galvanometer, Battery eliminator, Ammeter, commutator,Rheostat, Plug key, Scale, connecting wires.

Theory:

The magnetic induction B at any point P on the axis of the coil is given by

210( + )Where

No. of turns in the coil = n Current through the coil = i

Radius of the coil = r Horizontal component of the earth’s field Be =

Distance of the point P from the centre of the coil = d

Horizontal component of the earth’s field Be = 0.38 oersteds.

When the coil is placed in the magnetic meridian, the direction of the magnetic field will beperpendicular to the magnetic meridian i.e. perpendicular to the direction of the horizontalcomponent of the earth’s field Be. When the deflection magnetometer is placed at any pointon the axis of the coil such that the centre of the magnetic needle lies exactly on the axis ofthe coil, then the needle is acted upon by two fields B and Be, which are at right angles to oneanother. Therefore, the needle deflects, according to tangent law as

B = Betanθ

The value of the horizontal component of the earth’s magnetic field is taken from thestandard tables. The intensity of the magnetic field at any point is calculated from equationsand verified .

Procedure:

Stewart and Gee’s apparatus consists of a coil of thick insulated wire of 2 to 50 turns woundon a ring shaped wooden frame of 15 to 20 cm in diameter. The frame is fixed vertically onthe wooden support. A wooden plant about 100 cm long and 6 to 8 cm broad is fittedhorizontally inside the wooden ring with equal lengths projecting to either side of the ring. Ascale is fixed to the plank along its length and supported at its ends.

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( )

WestWestWest

EastWestWest

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1. With the deflection magnetometer draw a chalk line on the work table to representthe magnetic meridian and also draw the line perpendicular to it.

2. Set the Stewart Gee’s galvanometer with its coil in the magnetic meridian.3. Connect as in figure keeping the ammeter and rheostat well away from the

deflection magnetometer. To start with set the magnetometer at the centre of thecoil and rotate it to make the ends of the aluminium pointer read (0,0).

4. Close the key K1 and adjust the rheostat till the magnetometer shows a deflection60o. Reverse the current with the commutator K2.

5. Record the deflections before and after reversal of the current by noting both endsof the pointer and thereby get the values of deflection their mean gives thedeflection for d = 0 cm.

6. Next, move the magnetometer towards east along the axis of the coil in steps of 2cm at a time. At each position close the key and note deflections before and afterremoval of current and find mean deflection θE.

7. Repeat the above process by shifting the magnetometer towards west from thecentre of the coil in steps of 2 m each time.

Observations are recorded in Table. Theoretical and experimental values of magneticinduction B at various positions from the coil are compared in Table.

A graph is plotted taking distance, d along X – axis and tanθ along Y-axis.

Result:

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Conductionband

Valence band

Conductionband

Valence band Valence band

Conduction band

S.No Temperature(K)heating Cooling

Saturationcurrent(Io)

1/Tfor graph(K-1 )

Log(I0 )

1

2

3

4

5

mA

V

thermometer

Pn Junctiondiode

Heating coil

1/T(K-1)

Current in (log i0)

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Determine the band gap of semiconductor using p-n junction

Aim: To determine the energy band gap of a p-n junction.

Apparatus: p-n junction diode, thermostat, voltmeter, ammeter, thermometer, and battery.Theory:The current I through a p-n junction for both signs of applied voltage V

I = I0 = [(exp)eV/(kT)-1] ………………. (1)

Where e = Fundamental electronic charge, K= Boltzmann’s constant , T=absolute Temp

For the silicon p-n junction and positive values of V the exponential term becomesgreater than 1. The current through the junction will increase exponentially with V. thedependence on energy gap occurs through the factor I0. I0 is due to that current that flowswhen the when the junction is biased negatively and is due to the thermal excitation ofelectrons across the energy gap after which they flow freely across the junction. A completetreatment of the problems shows that I0is proportional to the factor f which is given by

F α T3/2 e-Eg/kT

E.g.=energy gap of the semi conducting material. The I0can be determined by a simplemeasurement with a negative bias applied to the junction. However, I0 is so small and carefulmeasurement is necessary. It is essential to generate curves representing equation (1) atseveral temperatures in order to obtain several values forI0.

Procedure:

1. The point contact diode connected in a reverse bias as shown in the diagram.2. It is placed in the oil bath and heated uniformly3. Saturation current is noted for various temperatures.4. The bias voltage is maintained at constant value.5. The readings in the micro-ammeter is noted as a function of temperature in steps of 50C.6. A graph is drawn between the log (1/T) in Kelvin on X-axis and logI0 is on y-axis.7. The slope o f the graph is calculated and substituted in the formulae.

Formula:Band gap energy Eg = 2.303 x 2 x k x slope eV

1.6x10-19

Precautions:

1. The current flow should not be too high, if the current is high the internal heating isoccur. This will cause actual temperature of the junction to be higher than themeasured value. This will produce non-linearity in the curve.

2. There may be contact potentials thermo emfs and meter dc offsets which must be addand subtract from the readings.

3. Poor contacts result in huge variations in the results and must be carefully soldered4. It is better to repeat a few measurements at the end of each run to check the source of

error.

Result : The energy gap of the p-n junction material is calculated= eV

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Forward Bias

VOLTAGE CURRENT

Reverse Bias

VOLTAGE CURRENT

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CHARACTERISTICS OF ZENER DIODE

AIM:

To observe and draw the static characteristics of a zener diode

APPARATUS: Regulated Power Supply - (0-30v),Voltmeter (0-20v), Ammeter, Zener

diode, Resistor.

THEORY: A zener diode is heavily doped p-n junction diode, specially made to

operate in the break down region. A p-n junction diode normally does not conduct when

reverse biased. But if the reverse bias is increased, at a particular voltage it starts

conducting heavily. This voltage is called Break down Voltage. High current through

the diode can permanently damage the device. To avoid high current, we connect a

resistor in series with zener diode. Once the diode starts conducting it maintains almost

constant voltage across the terminals what ever may be the current through it, i.e., it has

very low dynamic resistance. It is used in voltage regulators.

PROCEDURE:

Forward bias: the experimental arrangement is shown in figure.The zener

diode is is connected in series with the 1k resistance and the Dc power supply.Care

should be taken to see that the positive terminal of dc power supply is connected to

the p-side (anode)of the diode.This ensures that the diode is in forward bias.

The input dc supply voltage is switched on.The input voltage Vi (that is the out

voltage of dc supply) is gradually increased from zero in suitable steps.At each step

voltage drops across the resistance (VR) and across the zener diode (Vz) are measured

with the EVM.The current (Iz) is calculated from the formula Iz=R

VR .As we are not

much interested in the forward bias here, only a few readings are taken in the forward

bias region.Readings are tabulated in the table1.

Reverse bias: connections are madeas shown in fig. The positive terminal of the dc

supply is now connected to the cathode of the zener diode .The reverse bias voltage-

the input dc supply voltage Vi is again gradually increased from 0 value in suitable

steps (0.1V). At each step VR and Vz are measured with EVM and Iz=R

VR is calculated.

Sufficient number of readings are taken in the reverse bias until there is a steep rise in

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the value of VR(that is, until there is a steep rise in the value of Iz).This is the region

of zener breakdown where Vz remains constant (but VR increases) even when Iz

increases sharply. Readings are tabulated in table 2.

MODEL WAVEFORMS

Forward and Reverse characteristics of a Zener diode

CALCULATIONS:

Zener Reverse Break down voltage (VZ):

In graph draw a line that meets most of the points in the reverse conduction region.

The X-int of that line yields the Zener reverse break down voltage.

Observed Zener break down voltage=

Zener Cut-in Voltage:

Zener cut-in voltage from graph=

PRECAUTIONS:

1. The terminals of the zener diode should be properly identified

2. While determined the load regulation, load should not be immediately shorted.

3. Should be ensured be ensured that the applied voltages & currents do not exceed

the ratings of the diode.

RESULT: Static characteristics of zener diode are obtained and drawn.

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Screw Gauge

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Vernier callipers

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Spectro meter

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Colour Coding of Resistor

Aim :to determine the resistance of a resistor by using colour coading

Apparatus: various resistors

Procedure: from the given below chart find out the resistance of given resistor.

Result: the resistant of a given resistor is _______