physics lab. manuals_001

7/23/2019 Physics Lab. Manuals_001

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Experiment No. 1

Object :To determine the moment of inertia of a flywheel about its own axis of rotation.

Apparatus : A strong and thin cotton string, flywheel, stop watch, some different weights, a meter scale and a piece of chalk.

Theory and formula:The flywheel consists of a heavy wheel with a long axle supported in bearings andits centre of gravity lies on its axis of rotation. Its mass in mostly concentrated in therim and its moment of inertia is large.

Fig. -

Fig. - !

The flywheel energy storage systems can store"deliver power for only a short period,a few seconds or minutes #without recharging$.If m mass, of the suspended weight #gm$

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v linear velocity of mass, cm"sec and% the angular velocity of the flywheel #radian"sec$

then moment of inertia of flywheel !mgh & mr ! %

I ' ---------------------------- %! #t( n"n$

where I )omentum of inertia of a flywheel #gm-cm!$r radius of the axle #cm$n *umber of revolutions during the descent mass #m$n *umber of rotations #revolutions$ after the weight has been

detached from the peg.g Acceleration due to gravity. #cm"sec!$

h The height #cm$ from the groundt time

The motion of the flywheel is uniformly retarded by the frictional forces at the axle,the angular velocity decrease and final velocity is +ero. The average value of angular velocity is

% ( % ! nThe average angular velocity ' ------------ ' -------- ' ----------------

! ! t

' / n " t

Procedure :#i$ Take a string whose length is less then the height of the axle from the ground

and tie a mass 0m1 on one of its end.#ii$ 2rap the other end of the string uniformly round the axle so that mass 0m1 is

slightly below the rim of the wheel.#iii$ 3ount the number of turns of the string 0n1 wound around the axle.#iv$ Allow the mass to fall and note down the time taken 0t1 when the mass is 4ust

detached from the axle.#v$ 5epeat the step 6 and / different 0n1 by winding different number of turns on

the axle.

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#vi$ Again repeat the step / for three different masses keeping the number of turns wounded on the axle same.

Obser ations :7ernier constant ' 88888cm.5adius of the axle r ' 88888cm.)ass m ' 88888gm.

9. *o. )ass of 2eight#m$ gm.

:eight of mass#h$ cm.

*o. ofrevolution tillthe massdetaches #n $

*o. ofrevolutionagainst thefriction #n!$

Time #t$ sec

!alculations :)ean corrected radius of the axle ' 88888.cm% ' / n ! " t ' 88888..sec -

m# !gh"%! & r ! $

I ' ------------------------------- ( n " n!

' 888888. gm. ; cm.! ' 888888..kg.m!# *ote < make similar calculation for I from other sets of observations $

)ean value of moment of inertia of flywheel ' 8888888.=g. m ! "esult : The moment moment of inertia of the flywheel about its axis of rotation ' 888kg m !

#ources of error and precautions :. The length of the string should be always less than the height of the axle of the

flywheel from the floor so that it may leave the axle before the mass strikes thefloor.

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!. The loop slipped over the peg should be >uite loose so that when the string hasunwound itself. It must leave the axle and there may be no tendency for it torewind in the opposite directions.

6. The string should be evenly wound on the axle, i.e there should be nooverlapping of or a gap left between. The various coils of the string.

/. To ensure winding to whole number of turns of string on the axle the windingshould be stopped, when almost complete the pro4ecting peg is hori+ontal.

?. To determine h measure only the length of the string between the loop and themark at the other end where the string left the axle before the start of theflywheel.

@. The string used should be of very small diameter compared with the diameter of the axle. If the string is of appreciable thickness half of its thickness should beadded to the radius of the axle to get the effective value of r.

. The fiction at the bearings should not be great and the mass tied to the end of the string should be sufficient to be able to overcome the bearing friction and soto start falling of its own accord.

B. Take extra care to start the stop watch immediately the string leaves the axle.C. The diameter of the axle should be measured at a number of points along its

length and at each point two readings of diameters at right angles to one another should be taken.

Experiment No. $Object :To determine the fre>uency of electrically maintained tuning fork by )elde1s method.

Apparatus :Dlectrically maintained tuning fork, frictionless pulley, set of weights, a battery,rheostat, a meter scale and connecting wire.

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Theory and formula:)elde1s electrically maintained tuning fork consists of a large tuning fork made of ferromagnetic alloy, whose shank is rigidly clamped to a heavy rectangular woodenboard.

#a$ In the transverse arrangement, the fre>uency n of the fork, is

n ' "! l E T"m ' "!l E )g"m #T ' )g $

#b$ In the longitudinal arrangement, the fre>uency n of the fork is

n ' " l ET"m ' "l E)g"m #T ' )g $

2here m is the mass per unit length of thread) is the total mass suspendedT is Tension applied to thread

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l is length of the thread in the fundamental vibration

Procedure :. lace a load of in a pan attached to the end of the wire and measure the tuning

length of the wire and ad4ust the position of pulley.!. Increase the load by repeat the experiment with the same tuning fork.6. *ow calculate the T ' )g #Tension$ by the formula for different mass./. *ote down the m #mass$ and length of the wire, calculate the mass per unit

length.?. 5epeat the experiment for longitudinal arrangement.

)ass of thread ' 8888..gmGength of thread ' 8888.cm.

Obser ations :

9.*o.

2eightof panmp

Goadmassm

Totalweight) '#mp ( m$

TensionT ' )g

*o.ofloopsx

Gength ofcorrespondingthreadL

Fre>uencyn ' "! l ET"m

T r a n s v e r s e

G o n g

i t u

d i n a

l

)ean fre>uency #Transverse$ ' 888888888888:+.)ean fre>uency #Gongitudinal$ ' 888888888888.:+.

!alculations :#a$ Transverse arrangement

T ' ) g n ' "! l ET"m

#b$ Gongitudinal arrangementT ' ) g n ' " l ET"m

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"esult :The fre>uency of the electrically maintained tuning fork.

#a$ Transverse arrangement ' 8888888:+.#b$ Gongitudinal arrangement '888888..:+

Percenta%e Error : 9tandard 7alue & Hbserved 7alue

ercentage Drror ' --------------------------------------------------- ; '9tandard 7alue

Precautions and #ource of Error :. The wire"thread should be uniform in diameter, thin and inextensible.

!. The friction at the pulley should be negligible.6. The weight of the scale pan should be added./. )easure the length of the thread should be a properly.?. The vibration of the thread"wire should not rotate.@. The transverse arrangement should be hori+ontal and longitudinal arrangement

should be vertical.. The transverse arrangement should be hori+ontal and longitudinal arrangement

should be vertical.

Experiment No. &

Object :To determine the dispersive power of a glass prism using spectrometer and mercurysource.

Apparatus :9pectrometer, mercury source, glass prism, magnifying lens and spirit level. Theory and formula:It is a measure of the changes of the refractive index of the medium with wavelength. The dispersive power of a prism is given by

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Fig. - !

v - r % ' -------------------

- where v refractive index for violet colour.

r refractive index for red colour.mean of refractive index of violet and red colour.

3alculate the value of , using #A ( Jm$ 9in --------------- ! ' ------------------------------------------------------------------ 9in A"!

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2here, A ' angle of prism.

Jm angle of minimum deviation

Procedure :A. 'or !alculation of A

#i$ First ad4ust the spectrometer to get parallel light beam and check whether the prism table is hori+ontal by spirit level.

#ii$ *ow put the prism on prism table such that the two refrecting edgesshould point towards the light source. The light should fall on both sidesof the prism.

#iii$ 5otate the telescope in the direction H and then along HK to see thediffraction pattern that is slit of white light on the crosswire of thetelescope. 2rite down the position of these two images from the vernier

scales. The difference between these two positions gives twice the valueof angle A.

(. 'or measurement of )m#i$ *ow remove the prism from the table. Lring the telescope to the straight

position and note down the reading.#ii$ ut the prism back on the table such that the rough face of the prism faces

the right with respect to the straight position.#iii$ 3hoose any two colour in the spectrum. 5otate the telescope to right side

and look for the slit of these two colour on the crosswire. *ote down theseposition from the vernier scale.

#iv$ The difference between this position of a particular colour with the positionof straight view will gives the angle of minimum deviation for that particular colour.

#v$ *ow calculate and %.

Obser ation :7ernier constant of the spectrometer 'A. Table for measurement of an%le A

9. *o. 7ernierreading

First positionof telescope

9econdposition oftelescope

! A A #Megree$

.

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!.

)ean A ' 8888.

L. Table for measurement of angle Jm #violet$9. *o 7ernier reading )inimum deviation

reading9traight positionreading

JmMiffrece

A. Table for measurement of angle Jm #red$9. *o 7ernier reading )inimum deviation

reading9traight positionreading

JmMifference

)ean Jm ' 8888.!alculations :The dispersive power

v - r % ' -------------------

-

where #A ( Jm$ 9in --------------- ! ' ------------------------------------------------------------------

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9in A"!3alculate the value of r and v, using

v 5.I. of violet colour, A angle of prismr 5.I of red colour Jm angle of minimum diviation

average 5.Ifor violet A ' 8888degrees

Jm '8888..degreesv ' 8888..

for red A ' 8888.degreesJm ' 8888.degrees

r ' 888888

"esult :The dispersive power of prism ' 8888888.

Percenta%e Error: 9tandard 7alue & Hbserved 7alue


Precautions and source of error :

. The wire"thread should be uniform in diameter, thin and inextensible.!. The friction at the pulley should be negligible.6. The weight of the scale pan should be added./. )easure the length of the thread should be a properly,?. The vibration of the thread"wire should be rotate.@. The transverse arrangement should be hori+ontal and longitudinal arrangement

should be vertical.

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Experiment No. *

Object :To determine the wavelength of sodium light by *ewton1s rings.

Apparatus : A plane glass plate, plano-convex lens of large radius of curvature, a travellingmicroscope, sodium lamp source, , magnifying lens and spirit level. Theory and formula:The arrangement for *ewton1s ring is shown in fig. . A plano-convex lens of largeradius of curvature is placed with convex surface on a plane glass plate, an air film isformed between the lens and glass plate. If monochromatic light source falls onnormally on this air film. The alternate bright and dak concentric rings is formed inthe air film and the centre of ring is dark. These rings are formed as a result of interference between the light waves from the lower and upper surfaces of the film.The wavelength N of the light is given by the formula

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Fig. &

*ewton1s ring

M! n(k - M! n N ' ---------------------- / k 5

2here M ! n(k is the diameter of #n(k$th ring.M! n is the diameter of nth ring.k an integer number of the rings.5 is the radius of curvature of the curved face of the plano-convex

lens.

Procedure :. The convex lens G is used only when we have to use a point sourse

otherwise using an extended source. The convex lens G is not re>uired.!. The surfaces of the glass plate and the plano-convex lens should be

thoroughly cleaned with spirit.6. The centre of plano-convex lens is well illuminated by ad4usting of glass plate

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/. The microscope is ad4usted so that the rings are clearly seen in the field of view. If the rings obtained are not circular then either the glass plate of lensor both are irregular. The circular rings are obtained it the point of contact isuniform. 9ometimes the central spot is bright. This is because contactbetween the lens and the plate is not perfect on account of the presence of dust particles.

?. The microscope is now moved to left and the cross wire is set on the !! th ring.5eading are taken for both on the main scale and the vernier scales. Thecross wire is than moved towards right #i.e., back$ for taking readings of different ring keeping a gap of ! #i.e., on !th, / th , @th, 8till !!th ring on righthand side.

@. The difference of the consecutive reading of left and right hand sides give thediameter of that ring. :ence, the mean value of M! n(k & M! n is calculated.

. )easure the radius of the curvature of plano-convex lens 5 by using formula

5 ' l!"@h ( h"! ' 88888cm.Mistance between the two legs

l ' 888..cm. l! ' 8888cm. l6 ' 8888..cm.

l ( l! ( l6 l ' ------------------------------ cm.

6

' 88888.cm.2here l ' mean distance between the two legs of the spherometer in cm.

a ' speherometer reading on convex surface in cm.b ' spherometer reading on plane surface in cm.

then #a & b$ ' hThe wavelength of sodium light is calculated from the formula. M! n ' /nN5

M! n(k ' /#n(k$N5

M! n(k & M! n ' /kN5

N ' #M! n(k & M! n$"/k5Obser ations :Geast count of the microscope ' 8888888..9.*o.

*o.of

)icroscope reading Miameter ofthe ring

Mn! '!#; !-; $cm!

M! n(k & M! n3m !

k#G.:.9.$3 #5.:.9.$3

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rings m #x$ m #x!$ Mn'#x !-x $ cm.

!alculations :The wavelength of sodium light is given by

N ' #M! n(k & M! n$"/k5

N ' 88888. A

"esult :The mean wavelength of sodium light N ' 8888..A

Percenta%e Error :

9tandard 7alue & Hbserved 7alueercentage Drror ' --------------------------------------------------- ; '

9tandard 7alue

Precaution and #ources of Error :. The monochromatic light #source$ should be ad4usted for maximum visibility.

!. Olass plate and lens should be cleaned properly with spirit.6. The cross wire should be focused on a bright ring tangentially.

/. 5adius of curvature should be measured carefully.?. The range of the microscope should be properly ad4usted.@. The lens used should be of large radius of curvature and be measured properly.

. The glass plate O inclined of an angle of /? .

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Experiment No. +

Object :To determine the specific rotation of canesugar solution with the help of polarimeter.

Apparatus :Gaurent1s half-shade polarimeter, a sodium lamp, filter paper, an eye-piece, abalance, source of light, sugar, a weight box, two beakers, a glass rod andgraduated cylinder. Theory and formula:The specific rotation at a given temperature and given wave length of light N isdefined as the observed angle of rotation P when plane polari+ed light is passedthrough a sample with a path length of decimeter and sample concentration of gram per milliliter.

Fig. &

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Fig. & !

P9 ' ----------- l ; c

5otation in Megreesi.e., ' ----------------------------------------------------------------- Gength in Mecimeters ; 3oncentration is gm"cc

and concentration c ' m"7,

P 7 9 ' --------------------- l mwhere, 9 ' specific rotation

l ' length of the tube #decimeter$ m ' mass of sugar #gms$ 7 ' volume of sugar solution

P ' is the rotation produced #degrees$Procedure :. To prepare a ! Q solution of sugar #! gm sugar and cc of water$.

!. *ow filter the solution in clean dry beaker.6. Take the clean polarimeter tube #*o dust particles$ and fill with pure water

#without air bubble$./. ut the tube in its position in the polarimeter and two halves of the half shade

device of the field appear une>ually dark.?. 5otate the analy+ing"analy+er nicol till two halves of the half shade device of the

field appear e>ually dark.@. Take the reading on the scale.. *ow note down the temperature of the sugar solution.

B. 5epeat the step to with ?Q, Q, ?Q,!?Q and !.!?Q sugar solutions.C. *ote down the length of the tube #decimeters$.

Obser ations :

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2eight of sugar ' 888888..gm.2eight of beaker ' 888888.gm.Total weight of #sugar ( beaker$ ' 888888.gm.Gength of the tube ' 888888.decimeter Temperature ' 888888. 33oncentration of the solution m"7 ' 88888888gm"cc9.*o.

9ugar solution 9cale of readingwith solution

5otations P )ean P P

cer

ccer cc Ist

positionIIndposition

Istposition

IIndositio

n

!alculations :The specific rotation 9 ' P v " l m "esult :The specific rotation of sugar solution ' 8888888.degrees.

Percenta%e Error :

9tandard 7alue & Hbserved 7alueercentage Drror ' --------------------------------------------------- ; '9tandard 7alue

Precautions and #ources of Error :. The wavelength of light and room temperature should be noted properly.

!. )ake sure no air bubble inside the tube.6. The polarimeter tube should be clean and dry./. The water should be pure # without dust particles$.?. The position of the :alf shade device should be set accurately.@. Take the reading of e>ually dark position properly.

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Experiment No. ,

Object : To determine the wave length of sodium light using diffraction grating.

Apparatus :a spectrometer, a diffraction grating of known grating element, sodium lamp and areading lens.

Theory and formula:If light from a narrow slit, rendered parallel by a lens, is made to fall on the grating andanother lens employed to converge the rays issuing from the grating. 2e obtain an

image if the slit along the same direction as the incident rays. This is the image of the+ero order and has the same colour as the source of light. 9urrounding this image oneither side are the images of the first order, the second order and so on. For heterogeneous light we have the first order spectrum, the second order spectrum etc.,on either side of the central image. If P be the angle of diffraction in the order n for anywavelength N then.

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Fig. &

n N9in P ' ------------

#e ( d$

#e ( d$ sin P N ' --------------------------

n

Thus, the necessary measurement with the grating for the determination of N are theangle of diffraction P and the order of the spectrum n.

Procedure :)ake the preliminary mechanical and optical ad4ustments of the spectrometer. Thenproceed as follows uency of the ultrasonic wave and v its velocity in the li>uid, thenf v ' Nl 8888888888888888.#ii$

thus, knowing N and n and measuring the angle of diffraction, the wavelength of

ultrasonic wave in the li>uid can be determined by using D>. #ii$.It is known that the velocity of sound wave in a li>uid is related to its bulk elasticity D bythe relation.

v ' E#D " U$ 888888888888888.#iii$where, U is the density of li>uid. Thus, knowing v we can calculate the bulk elasticity of the li>uid. The reciprocal of this bulk elasticity D is known as the compressibility = of the li>uid, i.e.,

= ' "D 888888888888888...#iv$Thus, compressibility of the li>uid can be determined by ultrasonic diffraction of li>uid.Procedure :

. Ad4ust the spectrometer, so that a well collimated beam of light is obtained fromthe collimator.

!. )ount the glass cell #with pie+oelectric crystal fixed on one of its side $ on theprism table and fill it by the given li>uid upto V of its height. The crystal shouldbe fully immersed in the li>uid.

6. Ad4ust the prism table so that the front and back faces of the cell are exactlynormal to the incident light. Also make sure that the pie+oelectric crystal in theli>uid is located in such a way that the ultrasonic waves generated by it travel in adirection perpendicular to the direction of light.

/. 9witch on the radio fre>uency oscillator and ad4ust its fre>uency to match withthe natural fre>uency of the crystal. 2hen this happens, diffraction pattern isobserved in the spectrometer telescope.

?. )easure the angle !P between the first order spectrum lines on either side of the undeviated image of the slit. Also, measure !P! , !P6, 8888.similarly.

@. *ote down the fre>uency of r.f. oscillator at which diffraction pattern is obtained.This is also the fre>uency of the ultrasonic wave in the li>uid.

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Obser ation and calculations :2avelength of light N 'Fre>uency of ultrasonic wave f 'Mensity of li>uid U '

9.*o.

Hrder ofdiffraction

7ernier I 7ernier II )ean P n nNNl ' ----------- 9in Pn

7elocity of ultrasonic wave in li>uid v Nl ' f 'Lulk Dlasticity D ' v! U3ompressibility = ' "D ' 88888.. *"m !

"esult :#i$ 7elocity of ultrasonic wave in the li>uid ' 888888.m"s#ii$ 3ompressibility of the li>uid ' 88888 *"m !

#ources of errors and Precautions :$ 3are should be taken to make sure that the li>uid is completely stationary before

experiment is started.!$ The pie+oelectric crystal should be completely immersed in the li>uid.6$ The incident light should be perfectly normal to the direction of propagation of

ultrasonic wave in the li>uid./$ The light used should be monochromatic.?$ As the angles measured is extremely small, angles should be observed very

carefully.

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Experiment No. 3

Object :To determine the value of modulus of rigidity of the material of a given wire with)axwell1s needle - dynamical method.

Apparatus :)axwell1s needle, a fairly thin and long wire of the material to be tested, clamps andchucks, screw gauge, a meter scale, a stop watch, a balance and a weight box.

escription of Apparatus9uspended hori+ontally by a vertical wire attached to its middle point and carrying withinit four cylinders made of rolled brass and each of length G"/. The four cylinders areidentical in dimensions. The two of them are solid and e>ual in mass, and theremaining two are hollow and also e>ual in mass.

Theory and formula:Get the two hollow cylinders be placed in the middle and the solid ones at the two ends

of the tube and let the combination be slightly rotated in a hori+ontal plane and thenreleased. The body will then execute 9.:. )., about the wire as the axis and the periodof oscillation is given by

T ' ! E I "c 888888888888888..# $2here I is the moment of inertia of combination about the wire as the axis and c therestoring couple per unit twist due to torsional reaction.

*ow let the positions of the hollow and solid cylinder be interchanged so that the solidcylinders are now in the middle. Then, if I! is the moment of inertia of the newcombination about the axis of rotation, the new period of oscillation is given by

T! ' ! E I !"c 888888888888888..#!$9>uaring D>s. # $ and #!$ and subtracting D>. #!$ from D>. # $, we get

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T ! & T! ! ' / !"c # I & I!$/ ! #I & I!$

2hence c ' ------------------------------ T ! & T! !

Lut c is also e>ual to nr / "!l, where r is the radius and l the length of the wire whosemodulus of rigidity is n

n r / / ! #I & I!$:ence -------- ' --------------------- !l T ! & T! !

B l #I & I!$

or n ' --------------------------- 888888888888888888#6$ r / # T! & T! ! $

*ow let m and m! be the masses of each of the hollow and the solid cylindersrespectively and I , I1 and IW be the moments of inertia of the hollow tube, the hollowcylinder and the solid cylinder respectively about a vertical axis passing through their middle points. Then, if G is the length of the hollow tube,

I ' I ( !I1 ( !m #G"B$! ( !IW ( !m! #6G"B$!

and I! ' I ( !IW ( !m! #G"B$! ( !I1 ( !m #6G"B$!

hence I & I! ' !m ! X #6G"B$! & #G"B$! Y & !m X#!G"B$! & #G"B$!Y ' #m ! & m$ G! "/

utting this value of #I & I!$ in D>. #6$

! l #m! & m$G!

' ------------------------------ 8888888888888.#/$ r / #T! & T! !$

This expression can be used to find the value of modulus of rigidity n of the material of the suspension wire.

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Procedure :9uspend a wire of about ? cm, length and . cm. in diameter of the material whosemodulus of rigidity is re>uired from a rigid support, and to its lower end fasten with asuitable chuck and a clamp the hollow tube of the )axwell1s needle at its middle pointso that it may remain hori+ontal. lace all the four cylinders of the )axwell1s needleinside the hollow tube, the tow hollow cylinders being in the middle and no portion of thesolid cylinder should be pro4ecting outside the tube. Then fix a light pointer in themiddle of the needle and place a strip of mirror with a straight line mark below thepointer in the e>uilibrium position.5otate the )axwell1s needle slightly in a hori+ontal plane and then release it, it willperform torsional oscillations. Legin timing the oscillations of the )axwell1s needle withan accurate stop-watch by observing the transits of the pointer past the mark on themirror when viewed vertically. Metermine twice the time for a large number of oscillations, say 6 and take at least two sets of observations with different number of

oscillations and thus find out the mean value of T.*ow interchange the positions of the hollow and solid cylinders fifing them properlyinside the tube. Again set the )axwell1s needle oscillating in a hori+ontal plane anddetermine the period T! as before. T! will be less than T.*ext measure the length of the hollow tube and that of the wire between the two clampsby a meter scale. Than measure with a screw gauge the diameter of the wire, now tofind out #m! & m$ put one solid cylinder in the left pan of a physical balance and one

hollow cylinder in its right pan, and by putting extra weights in the right pan, find thedifference between the masses of the two cylinders. 9imilarly determine the differencebetween the masses of the other two cylinders. From these two weighing, find out themean value of #m! & m$. If a balance of high capacity and suitable sensitivity isavailable, the value of #m! & m$ may be found by a single weighing. Finally calculatethe value of modulus of rigidity of the material of the wire from e>uation #/$.

Obser ations :

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#A$ Metermination of T and T! Geast count of stop-watch ' 888..sec.9. *o. *o. of

oscillations

Metermination of T Metermination of T!Time taken T sec. Time taken T! sec.)in. 9ec. )in. 9ec.

!

6/?)ean )ean

#L$ #i$ Gength of the wire ' 88888.cm. #ii$ )easurement of diameter of the wire ' 88888 cm.

#iii$ least count of screw gauge ' 8888....cm. Zero Drror ' 88888 cm.

9. *o. 5eading along any

diameter acm.

5eading along

perpendicular diameter bcm.

a ( b!cm.

)ean uncorrected diameter)ean corrected diameter ' 88888 cm.#3$ #i$ length of the hollow tube ' 888888.cm.

#ii$ Metermination of #m & m!$ Mifference between the masses of one solid and one hollow cylinder '..8gm. Mifference between the masses of other pair of solid and

hollow cylinder' 8888...gm. )ean value of #m ! & m$ ' 88.gm.

!alculations :

)ean radius of the wire ' 888.8cm. ! l #m! & m$G!

n ' ------------------------------ r / #T! & T! !$

' 8888888.dynes"cm ! "esult :

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The value of modulus of rigidity for the material of the wire '88888. dynes"cm !

9tandard value ' 8888... dynes"cm !

Drror ' 88888..Q#ources of error and precautions :4

. The two sets of cylinders should be exactly identical and the hollow tube shouldbe clamped exactly in the middle.

!. The )axwell1s needle should always remain hori+ontal so that the moment of inertia of the hollow tube about the axis of rotation remains unaltered throughoutthe whole experiment. :ence while placing the cylinders inside the tube, noportion of them should be left pro4ecting outside the hollow tube.

6. The motion of the )axwell1s needle should be purely rotational in a hori+ontalplane. All undesirable motions #up and down, or pendular$ should be completelychecked.

/. As in the expression for n the periods occur raised to the second power, theymust be carefully measured by timing a large number of oscillations with an

accurate stop-watch upto an accuracy of say, . of a second.?. The wire should not be twisted beyond elastic limit otherwise the restoring couple

due to torsioanl reaction will not be proportional to value of the twist.@. There should be no kinks in the wire. The wire should be fairly long and thin

particularly when the rigidity is high so that the restoring couple per unit twist dueto torsional reaction may be small and hence the period of oscillation of the)axwell1s needle is large.

. In the expressional for n the radius occurs raised to the fourth power and is a

very small >uantity usually of the order of . cm. :ence the diameter must bemeasured very accurately. 5eadings should be taken at several points e>uallyspaced along the wire and two diameters at right angles to each other should bemeasured at each point, care being taken not to compress the wire in taking thereadings.

Experiment No. 5

Object : To find the wave length of :e-*e laser using transmission diffraction grating.

Apparatus ::e-*e Gaser, Miffraction grating, screen, stands, meter scale and power supply.

Theory and formula:

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GA9D5 stands for [Gight Amplification by 9timulated Dmission of 5adiationW,2hen a parallel beam of monochromatic light of wave length N be incident normally on adiffraction grating. It is diffracted by the diffraction grating. The principal maxima of nth

order is given by

Fig. -

#e ( d$ sin Pn ' n N

#e ( d$ sin Pn N ' -------------------------

n

where, e ' the width of each slitd ' the width of each opa>ue space between two slitsPn ' an angle of #Miffraction$n ' order#e(d$ ' grating element #inch$#e(d$ ' !.?/"* per cm.

* ' *o. of lines on a grating per inch.

Procedure :#i$ 9et the :e-*e laser source hori+ontally.#ii$ lace the diffraction grating between :e-*e laser source and screen.#iii$ Find out the principal maximum, Ist and IInd order maximum.

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#iv$ *ow measure the distance between diffraction grating and screen that is M#cm.$

#v$ )easure the distance from principal maximum to Ist maximum that is d #n' $.#vi$ *ow find out the value of 9in P by formula.#vii$ 5epeat the steps & @ three times for different distance M and note down the

reading.

Obser ations :*o. of lines on the Miffraction grating * ' 88..per inch.

!.?/Orating Dlement #e ( d$ ' ------------ per cm. *9. *o. Hrder n Mistance between

screen and diffraction

M #cm.$ M #cm.$grating

Mistance ofmaximum from

central point H#dn$ cm.

dn9in Pn ' -------------

E#M! ( d n!$

!6/?

If M \\ dn than, 9in Pn ' d n " M

!alculations :n N ' #e ( d$ 9in Pn

#e ( d$ 9in PnN ' ---------------------- A

n

#e ( d$ ' 888888..per cm.n ' 8888..9in Pn ' 8888..

Than, find out N '8888.. AN! '8888.. A

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N6 '8888.. A

# N ( N! ( N6 $)ean N ' ---------------------------- ' 888888.. A 6

"esult :The wave-length of :e-*e laser ' 8888.. A

Percenta%e Error : 9tandard 7alue & Hbserved 7alue


Precaution 6 #ources of Error :$ The plane diffraction grating should be very close to the :e-*e laser source.

!$ The :e-*e laser source should be :ori+ontal. The grating element #e(d$ shouldbe in cm.

6$ Ad4ust the distances between diffraction grating and screen properly./$ 5uled surface of the diffraction grating should be vertical.?$ The diffraction grating should be handled by the edges.

Experiment No. 17

Object : To determine the fre>uency of a tuning fork by means of a sonometer.

Apparatus :9onometer with weights, tuning fork, meter rod, balance, paper riders and a rubber

cork.Theory and formula: A sonometer is a long, hollow wooden box, having two fixed knife-edges A and L and aedge 3. a wire has its one end tied to a hook :, the other end passes over a smoothfrictionless pulley and carries a load. If 3 be removed and the wire pressed at themiddle and let go, it vibrates as a whole in one segment with nodes at A and L and an

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antinode midway between them. If the wire is held at the middle and one segmentpressed and let go, it vibrates in two segemtns. If held at the one third and the shorter segment pressed, it vibrates in three segments and so on.

8#onometer9*ow n ' v"N, also for a stretched string

v ' E#T"m$where T is the tension on it and m ' mass of cm. of wire. n ' "N E#T"m$

or in general n p;$l


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#iii$For greater accuracy, vibrate the wire as well as the fork and try to listen to_beats1 between the two sounds. The beats are then made to disappear bysliding 3. the two fre>uencies are now e>ual.

#iv$ erform the experiment thrice and determine the mean lengthl ' A3. 5epeatthe observation with various loads put on the wire.

#v$ Take a measured length of wire and determine its weight accurately and hencefind m, the mass of cm, of wire.

Obser ations : Gength of wire ' 88888.cm.

)ass of wire ' 88888 gm.)ass"length ' 88888 gm.

9. *o. Goad or Tension )#grams$

7ibrating length l #cm.$ n ' "! l E#)g"m$

!alculations :n ' "! l E#)g"m$

"esult :The fre>uency of the tuning fork ' 8888.. cycles"sec.

#ources of Error and Precautions :. The wire should be stretched hori+ontally i.e. A, L, 3 and the pulley must all be in

one plane.!. The tuning fork should never be struck on a hard surface. Its tip should be struck

gently on a rubber cork.6. The beats must be eliminated to determine the correct vibrating length.

=ea> Points :. The resonance point may not be exact.

!. The fre>uency of the fork may differ slightly from the value marked on it.

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Experiment No. 11

NA E9tudy of *umerical Aperture of Hptical fiber.

O(?E!T@-EThe ob4ective of this experiment is to measure the numerical aperture of the plastic fiber provided with the kit using @@ nm wavelength GDM.

T EO"B*umerical aperture refers to the maximum angle at which the light incident on the fiberend is totally internally reflected and is transmitted properly along the fiber. The coneformed by the rotation of this angle along the axis of the fiber is the cone acceptance ofthe fiber. The light ray should strike the fiber end within its cone of acceptance, else it isrefracted out of the fiber core.

!ON#@ E"AT@ON# @N N.A. EA#C"E ENTIt is very important that the optical source should be properly aligned with thecable ` distance from the launched point ` the cable is properly selected toensure that the maximum amount of optical power is transferred to the cable.

! This experiment is best performed in a less illuminated room.

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EDC@P ENT#Dxperimental =it Fiber Gink & A, meter fiber cable, Fiber holding fixture, 5uler.

P"O!E C"E

9lightly unscrew the cap of GDM 9F: ?@7. Mo not remove the cap from theconnector. Hnce the cap is loosened, insert the fiber into the cap. *ow tightenthe cap by screwing it back.

! *ow short the 4umpers as shown in the 4umper diagram. 5emove 4umper caps of ` .

6 3onnect the power cord to the kit ` switch on the power supply. =eep switchnear power connector at lower position.

/ Apply 9KSA5D H" signal to LSFI" ` short H" to T; I" .? Insert the other end of the fiber into the numerical aperture measurement 4ig.

:old the white sheet facing the fiber. Ad4ust the fiber such that its cut face isperpendicular to the axis of the fiber.

@ =eep the distance of about mm between the fiber tip and the screen. Oentlytighten the screw and thus fix the fiber in the place.*ow observe the illuminated circular patch of light on the screen.

B )easure exactly the distance d and also the vertical and hori+ontal diameters)5 and * indicated in the fig.

C )ean radius is calculated using the following formula5 ' #)5 ( *$"/

. Find the numerical aperture of the fiber using the formula*A ' sin P max ' r " E#d! ( r!$2here P max is the maximum angle at which the light incident is properlytransmitted through the fiber.

Experiment No. 1

Object : To determine the value of e"m of electron by . . Thomson method.

Apparatus :3athode ray tube with its power supply, pair of bar magnets, compass box, woodenstand to place bar magnets.

Theory and formula:3.5. tube is basically made up of there components ual resistance, thick copper strips, afactional resistance box, galvanometer, unknown small resistance wires, a single wayplug =ey etc.

Theory And 'ormula :

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3arey Faster1s bridge is specially suited for the comparison of two nearly e>ualresistance whose difference is less than the resistance of the bridge wire.

3arey Foster bridge is a modified form of slide wire bridge in which and K are ratioarms, ; is resistance between #A ` M$ and is resistance #3`M$

If = be the resistance per unit length of wire, N ` N! be the end resistances at A1 and L1and A1M ' l is balancing length as shown in Fig. #a$

There we have ;(l k(N --------- ' ----------------------------- 8888888# $

K ( # & l $k ( N!

If, ; and are interchanged and the balance point shifts to M1 as shown Fig. #b$ so that A1M ' l! .

( l!= ( NThan ------- ' --------------------------------------- 88888888 #!$ K ; ( # & l $= ( N!

3ompare #i$ and #ii$ and add one to both sides, get

;( ( =( N ( N! ;( ( =( N ( N! -------------------------------- ' ------------------------------

( # & l$= ( N! ; ( # & l!$= ( N!

or ( # & l$= ( N! ' ; ( # & l!$= ( N!

or ; & ' #l ! & l$=

2here ; is unknown resistance #l ! & l$ is shift in balance point, when position of ; and are interchanged. In general, let d and d ! be the shift corresponding to resistance

and ! than

; & ' d = 888888888888.#6$

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; & ! ' d ! = 888888888888#/$

From e>uation #6$ and #/$

; & d we have, ------------- ' ------ ; & ! d!

d! ; & d! ' d #; & !$

#d! & d$ ; ' d ! & d !

d! & d ! ; ' ----------------------- d! & d Procedure :

$ )ake connections as shown Fig. #a$ and #b$.

!$ 2hen the circuit completed keep ; and at +ero value and find balance point.

Interchange ; ` and again find balance. The difference between these tworeading gives correction l to be applied to the various readings.

6$ 5eplace strip of gap by unknown resistance ; and strip of gap / by . Findbalance point.

/$ 5epeat step 6 for ' .!, .6, ./, .? etc.

Obser ations :

3orrection to be applied, l ' 888 cm.

9.*o.

=nownresistance

#ohm.$

osition of balance pointwith in

Mifference#l & l!$

3orrected 9hiftd ' #l & l!$ - l

Snknownresistance # $

d! & d !

; ' --------------- d! & d

Geft gap l 5ight gap l!

.!.6./.?.

Page | 44


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!alculations :

The unknown resistanced! & d y!

; ' --------------------------d! & d

here d and d! be the shift corresponding to resistance y and y!.

"esults :

Find value of ; using reading of observations ` !, !`6, 6`/ 88..and so on.

Percenta%e Error : 9tandard value & observed value

Q error ' ---------------------------------------------- ; ' 888Q 9tandard 7alue

Precautions and #ources of Error :

$ All the terminals should be tight and the ends of the connecting wires should beclean.!$ A plug key should be included in the cell circuit and should be closed whenobservation are being made.

6$ The cell circuit should be closed depressing the 4ockey over the bridge wire, butwhen breaking, reverse order should be followed.

/$ The connections should be tight and the plugs of the resistance box should begiven twist so that they are tight.

?$ The connecting wires and the copper strip should be thoroughly cleaned withsand papers.

@$ For bridge to have high sensitivity, the resistance of the four arms should be of the same order.

$ The difference between and K should not be more than the resistance of thebridge wire.

Experiment No. : &

Object :To study the charging and discharging of a capacitor and to find out the time constant.

Apparatus :

3harging and discharging kit, stop watch and 3onnecting Geads.

Theory and 'ormula :

A Capacitor is a passive device that stores energy in its E ectric !ie d and ret"rns energy to thecirc"it #henever re$"ired% A Capacitor consists o& t#o Cond"cting P ates separated 'y an

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(ns" ating )ateria or *ie ectric% !ig"re 1 and !ig"re 2 are the 'asic str"ct"re and the sche+aticsy+'o o& the Capacitor respective y%

!ig"re 1, -asic str"ct"re o& the Capacitor

!ig"re 2, .che+atic sy+'o o& the Capacitor

/hen a Capacitor is connected to a circ"it #ith *irect C"rrent *C so"rce t#o processes#hich are ca ed charging and discharging the Capacitor #i happen in speci&ic conditions%

(n !ig"re 3 the Capacitor is connected to the *C Po#er ."pp y and C"rrent & o#s thro"gh thecirc"it% -oth P ates get the e$"a and opposite charges and an increasing Potentia *i&&erence v cis created #hi e the Capacitor is charging% nce the o tage at the ter+ina s o& the Capacitor v cis e$"a to the Po#er ."pp y o tage v c the Capacitor is &" y charged and the C"rrent stops& o#ing thro"gh the circ"it the Charging Phase is over%

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!ig"re 3, he Capacitor is Charging

A Capacitor is e$"iva ent to an pen Circ"it to *irect C"rrent : ; 'eca"se once theCharging Phase has &inished no +ore C"rrent & o#s thro"gh it% he o tage v c on a Capacitor

cannot change a'r"pt y%

/hen the Capacitor disconnected &ro+ the Po#er ."pp y the Capacitor is discharging thro"ghthe :esistor : * and the o tage 'et#een the P ates drops do#n grad"a y to


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!ig"re 5, he o tage v c and the C"rrent iC d"ring the Charging Phase and *ischarging Phase

he s+a er the :esistance or the Capacitance the s+a er the i+e Constant the &aster thecharging and the discharging rate o& the Capacitor and vice versa%

Capacitors are &o"nd in a +ost a e ectronic circ"its% hey can 'e "sed as a &ast 'attery% !ore>a+p e a Capacitor is a storeho"se o& energy in photo& ash "nit that re eases the energy $"ic? yd"ring short period o& the & ash%

Obser ations and !alculations :

)ax voltage of capacitor ' 888888.. 7olts

9. *o. 5esistance5 # $

3apacitance3 #F$

T charging#sec.$

T! #discharging$#sec.$

53

.!.6./.?.@.

"esult :

Dxperimental value of time constant is within percentage error limits.

Precautions and #ources of Error :

$ The electrical connections should be made carefully.!$ Time for charging and discharging should be noted very carefully.6$ roduct of 5 and 3 should not be very small.

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Experiment No. : *

Object :To study the thermo e.m.f. using thermocouple.

Apparatus :

A Iron-constantan thermocouple, thermocouple kit, a water bath, a funnel, a clamp, atwo way key, ice, beaker and connecting wire. Theory and 'ormula :

Thermoelectricity refers to the phenomena that occur at the 4unctions of dissimilar conductors when a temperature difference exists between the 4unctions. The samephenomenon occurs within a single conductor too, with the two ends are maintained atdifferent temperatures.In this section, we discuss three such phenomena, namely 9eebeck effect, eltier effectand Thomson effect, discovered historically in this order. These involve conversion of thermal energy into electrical energy or voce versa.Smber the oule effect, all the abovethree effects are reversible with respect to the direction of the current and reversal of temperature difference. The 9eebeck effect is a combination of eltier and Thomsoneffects.

#eebec> EffectThis effect is named after common ohann 9eebeck, a Oerman physicist, whodiscovered it in B! . :e found that Lismuth, are 4oined at their ends #called a 4unction$

through a sensitive galvanometer, and the two 4unctions are kept at differenttemperatures, then the galvanometer shows a deflection. This emf generated in thecircuit is called thermoelectric emf or thermo-emf, for short. The resulting current isknown as thermoelectric current. The two 4unction circuit is called a thermocouple, andis known below.

This effect is called thermoelectric effect because heat energy is directly converted intoelectrical energy.

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The thermo-emf produced is very small, of the order of m7 per every degree of temperature difference. The 9eebeck effect is reversible, i.e., if the hot and cold 4unctions are interchanged, the direction of emf #and hence current$ reverses.The magnitude and direction of thermo-emf depends on the materials forming thethermocouple and the temperatures of the ! 4unctions.9eebeck conducted a number of experiments by forming thermocouples of differentmetals. :e arranged the metals in a series such that in a thermocouple formed from anytwo of them, current will flow from a metal earlier in the series to the one later in theseries through the cold 4unction. This is called the thermoelectric series. art of theseries isuid #=erosene Hil$.

Apparatus :5. F. oscillator, pie+o electric crystal, spectrometer # ultrasonic$, glass cell, light source#sodium lamp$.

Theory And 'ormula :2hen ultrasonic waves are passed through a li>uid, a diffraction pattern similar to thoseas observed in ruled grating is formed.The ultrasonic waves passing through a li>uid are elastic waves and formscompressions and rarefactions in the li>uid. These compressions and rarefactions after reflection form sides of a cell form a stationary wave pattern in which nodes andantinodes are spaced periodically. Mue to this density and hence refractive index of medium also shows periodic variation with distance from the source along the directionof propagation of as diffraction grating Xwhere grating element #a(b$ e>ual to wavelength of ultrasonic wave i.e. Nu Y. 9uch a grating is known as acoustic grating.

2hen the crystal is at rest, a single image of the slit is observed. Lut when ultrasonicwaves are produced in the li>uid, a number of diffracted images appear on either side of the central image. The angular separation P between the direct image of the slit and thediffracted image of any order, say 0n1 is measured.

Ssing the theory of diffraction grating the wavelength of ultrasonic waves can becalculated.

If N is the wavelength of the sodium light then.

Nn sin Pn ' nN

nN Nn ' -------------- 9in Pn

If v is the fre>uency of ultrasonic oscillations. The velocity of ultrasonic wave, inli>uid 7 can be written as

7 ' v N n

Procedure :. 9etting of spectrometer

#a$ 5otate the telescope and focus it on some distant ob4ect. )ake clear imageof distant ob4ect with the help of rack and pinion arrangement. The telescope

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is in a position to focus parallel beam of rays coming from distant ob4ect atfocus. Mo not disturb this position through out the observations.

#b$ Lring telescope in line with the collimator. Illuminate the slit of collimator withlight source #sodium light $ and ad4ust its width with the help of ad4ustingscrew provided on the slit. Gook through the telescope and ad4ust rack andpinion arrangement of collimator till a clear image of slit is observed. In thisposition, the collimator is providing parallel beam of rays.

!. 9etting of glass cell < mount the glass cell on the prism table and fill it with thegiven li>uid upto V of its height. Turn the prism table the front and back faces of cell are perpendicular to the incident light.

6. Immerse the pie+oelectric crystal in the li>uid and rotate it such that theultrasonic waves generated by it travel in a direction perpendicular to thedirection of propagation of light. 3onnect the crystal to the output terminal of the5.F. oscillator.

/. 9witch on the 5.F oscillator and ad4ust its fre>uency to match with the naturalfre>uency of the crystal. At this instant resonance takes place and diffractionpattern will be observed in the spectrometer telescope. Ssually five line includingslit are seen in the telescope on either side.

?. )easure angle !P between first order spectral line similarly !P!, ! P 6 and so onbetween higher order spectral lines on either side of central maxima. *ote downthe fre>uency of 5F oscillator.

@. 5epeat for higher order maxima.

Obser ations and calculations :Page | 55


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2ave length of sodium length #N$ ' ?BC6A 5oom temperature ' 888.. 3Fre>uency of 5.F. Hscillator v ' 8888 :+Mensity of oil ' 8888 gm"cc

#for kerosene ' .B gm"cc$Obser ation Table :

#. No. Order ofdiffractionpattern 8n9

Position of ima%e b a0n 44444444 $

ean 0 n nFlu 44444 sin 0 n

)ean value of N u ' 8888888m7elocity of ultrasonic 7 ' v Nu ' 88888.. m"sec.

"esult :7elocity of ultrasonic waves travelling in li>uid is found to be 8888..m"sec.

Percenta%e Error : 9tandard value & observed value

Q error ' ---------------------------------------------- ; ' 888Q 9tandard 7alue

Q error in the velocity of the ultrasound is 888888.. m"sec.

Precautions and #ources of Errors :$ The spectrometer should be ad4usted carefully and rack and pinion

arrangement of telescope should not be disturbed throughout theobservations.

!$ 3ell should be thoroughly cleaned and filled with li>uid upto V of its height.6$ The crystal slab should be immersed completely in li>uid and should not

touch to bottom and wall of the cell./$ The crystal slab should be rotated till the ultrasonic waves produced by it

travel perpendicular to incident light.?$ Fre>uency of 5.F oscillator should be ad4usted properly for resonance.@$ attern should be narrow and sharp.

Experiment No. : ,

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Object :To study the different wave form like sine wave ` s>uare wave and measure the 7p-p,7p, 7rms, Amplitude, Time period and fre>uency by oscilloscope.

Apparatus :35H #3athode 5ay Hscilloscope$, two function generator, connecting leads etc.

Theory And 'ormula :!"O 8!athode "ay Oscilloscope9 & cathode-ray oscilloscope, electronic-displaydevice containing a cathode-ray tube #35T$ that generates an electron beam that isused to produce visible patterns, or graphs, on a phosphorescent screen. The graphsplot the relationships between two or more variables, with the hori+ontal axis normallybeing a function of time and the vertical axis usually a function of the voltage generatedby the input signal to the oscilloscope. Lecause almost any physical phenomenon canbe converted into a corresponding electric voltage through the use of a transducer %

easurin% olta%e and time period

The trace on an oscilloscope screen is a %raph of olta%e a%ainst time. The shape of this graph is determined by the natureof the input signal.In addition to the properties labelled onthe graph, there is fre>uency which isthe number of cycles per second.

The diagram shows a sine /a e butthese properties apply to any signalwith a constant shape.

Amplitude is the maximum voltage reached by the signal.It is measured in olts, - .

Pea> olta%e is another name for amplitude.

Pea>4pea> olta%e is twice the peak voltage #amplitude$. 2hen reading anoscilloscope trace it is usual to measure peak-peak voltage.

" # olta%e 8 root means sGuare olta%e 9 : 7 rms ' 7 " E!

Time period is the time taken for the signal to complete one cycle.It is measured in seconds 8s9 , but time periods tend to be short so milliseconds8ms9 and microseconds 8Hs9 are often used. ms ' . s and

s ' . s.

'reGuency is the number of cycles per second.It is measured in hertI 8 I9, but fre>uencies tend to be high so >ilohertI 8> I9and me%ahertI 8 I9 are often used. k:+ ' :+ and ):+ ' :+.

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http://www.britannica.com/EBchecked/topic/99774/cathode-ray-tube-CRThttp://www.britannica.com/EBchecked/topic/183490/electron-beamhttp://www.britannica.com/EBchecked/topic/602499/transducerhttp://www.britannica.com/EBchecked/topic/183490/electron-beamhttp://www.britannica.com/EBchecked/topic/602499/transducerhttp://www.britannica.com/EBchecked/topic/99774/cathode-ray-tube-CRT


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fre>uency ' and time period ' time period fre>uency

Procedure :

-olta%e

7oltage is shown on the ertical y4axis and the scale is determined by the A) GIFID5 #7HGT9"3)$ control. Ssuallypea>4pea> olta%e is measured because itcan be read correctly even if the position of 7 is not known. Theamplitude is half thepeak-peak voltage.

If you wish to read the amplitude voltage directly you must check the position of 7

#normally halfway up the screen$< move the A3"O*M"M3 switch to O*M # 7$ and use -9:IFT #up"down$ to ad4ust the position of the trace if necessary, switch back to M3afterwards so you can see the signal again.

-olta%e distance in cm J olts;cm Example: peak-peak voltage = 4.2cm 2V/cm = 8.4Vamplitude (peak voltage) = peak-peak voltage = 4.2V

Time periodPage | 58

The trace of an A3 signal

A) GIFID5< !7"cmTI)DLA9D< ?ms"cm

Example measurements:

peak-peak voltage ' B./7amplitude voltage ' /.!7

time period ' ! msfre>uency ' ? :+


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Time is shown on the horiIontal x4axis and the scale is determined by the TI)DLA9D#TI)D"3)$ control. The time period #often 4ust calledperiod $ is the time for one cycleof the signal. The freGuency is the number of cyles per second, fre>uency ' "timeperiod

Obser ation Table :

'or sine /a e#.No.

Amplitude -p4p -p -p4p ; $ -rms -p ; uency of the audio-oscillator should be slowly ad4usted so as to lock the

pattern.

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Experiment No. : 2

Object : Sse the )ultimeter to measure the 5esistance and M.3 voltage.

Apparatus :

)ultimeter, M.3. voltage supply, resistance box and connecting leads. Theory :

A meter is a measuring instrument. An ammeter measures current, a oltmeter measures the potential difference #voltage$ between two points, and anohmmeter measures resistance. A multimeter combines these functions, and possibly someadditional ones as well, into a single instrument.

Procedure :

Lefore going in to detail about multimeters, it is important for you to have a clear idea of how meters are connected into circuits. Miagrams A and below show a circuit before

and after connecting an ammeters. # $ and #!$, we have

5 ( r l r l ------------ ' ------- ( ------ ' -------------

5 l ! 5 l !

r ' X l " l! - Y 5 ------ #6$

Procedure :. )ake the electrical connections as shown in Fig.

!. 5emove the insulation from the ends of copper wires and clean the ends withsand paper. 3onnect the positive pole of auxiliary battery to the +ero end #A$ of the potentiometer and negative pole through a one way key, an ammeter and

low resistance rheostat to the other end #L$ of the potentiometer wire.6. 2ith a certain setting of rheostat and by closing key = , obtain a balance point.*ote the length of this point from the end A. This gives the length l.

/. *ow introduce a suitable resistance in the resistance box 5 #low resistance$ andclose the key =! . Again obtain the length l! of the potentiometer wire where thenull point is obtained. This gives l! .

?. 5epeat the experiment for different values of resistance 5.@. 3alculate internal resistance of Geclanche 3ell using D>. #6$.

Obser ations :

Obser ation Table9. *o. Lalancing

length #l $5esistance#5$

Lalancinglength #l!$

r ' X l " l! Y 5

)ean r

!6/?

!alculations :

r ' X l" l! Y 5 '

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"esult :

The internal resistance of Geclanche cell using potentiometer ' 888888.. .

Precautions :. The internal resistance of a Geclanche cell is not constant but varies with current

drawn from the cell. :ence to get suitable readings the resistance from theresistance box must be varied by small amount # to @ $.

!. The e.m.f. of the battery should be greater than that of the Geclanche cell.6. The positive terminals should be connected at point A.4% A high resistance should be connected in series with the galvanometer.

physics lab. manuals_001

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