experiments 26.11

7/28/2019 Experiments 26.11

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SREEPATHY

INSTITUTE OF

MANAGEMENT

ANDTECHNOLOGY

Vavannoor, Palakkad District

LAB MANUAL

EN 09 103 P ENGINEERING PHYSICS


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INDEX

Sl.No Name of the Experiment Page No

1 Zener diode Characteristics 3

2 Transistor Characteristics 6

3 Grating Normal incidence 104 Grating - Diffraction 15

5 Voltage regulation using Zener Diode 18

6 Newtons Rings 21

7 Photo Diode Characteristics 258 LED Characteristics 27

9 Grating Dispersive power 3010 Grating Resolving power 34

11 Air wedge 37

12 Meldes Experiment 40


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EXPERIMENT I

CHARACTERISTICS OF ZENER DIODE

AIM:

To study and draw the forward and reverse bias characteristic of Zener

diode.

APPARATUS:

Zener diode characteristics apparatus

PRINCIPLE:

In the forward biased condition Zener diode acts as the normal diode. But inthe reverse biased condition the reverse current shoots up at a particular voltagecalled Zener voltage or breakdown voltage.

PROCEDURE:

FORWARD BIAS CHARACTERISTICS1. Initially the apparatus is in switched off position.2. The switch just below the voltmeterM is kept towards forward side.3.

The switch just below the ammeterM is kept towards forward side.4. The switch just below Zener diode is kept toward forward side.

5. The apparatus is switched on.6. Voltage V is increased in small steps by using potentiometer P and

corresponding current I in milliammeter is noted.7. A graph is drawn by taking V on X- axis and I on Y- axis.8. The apparatus is switched off.


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REVERSE BIAS CHARACTERISTIC1. Initially the apparatus is in switched off position.2. The switch just below the voltmeterM is kept towards reverse side.3. The switch just below the ammeterM is kept towards reverse side.4. The switch just below Zener diode is kept toward reverse bias side.5. The apparatus is switched on.6. Voltage V is increased in small steps by using potentiometer P and

corresponding current I in milliammeter is noted.

7.

A graph is drawn by taking V on X- axis and I on Y- axis.8. The apparatus is switched off.


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OBSERVATION:

Least count of voltmeter in forward bias = .V.Least count of ammeter in forward bias =mA.Least count of voltmeter in reverse bias = .V.Least count of ammeter in reverse bias =mA.

CALCULATION:

Dynamic resistance (r) = =

=

()()

r= ...........................Ohms.

RESULTS:

The characteristics of Zener Diode in forward bias are similar to thecharacteristics of P-N Junction diode in the same mode.

Zener Voltage =.Volt.

Forward (dynamic) resistance= . Ohms.


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EXPERIMENT II

STATIC TRANSISTOR CHARACTERISTICSAIM:

To draw the static characteristic of a transistor in common emitter

configuration and hence to calculate (i) input resistance (ii)output resistance and(iii) current gain of the transistor.APPARATUS:

Transistor characteristics apparatusPROCEDURE:

Connections are made as shown in the circuit diagram.


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INPUT CHARACTERISTICS1. Input characteristic is a graphical relation between the input current and

the input voltage for a constant output voltage .2. The voltage is kept constant at 0V by adjusting the potentiometer P2.3.

The base current is kept at 0A by using potentiometer P1.4. The emitter to base voltage is noted.

5. The base current is increased in steps of 25A and corresponding VBE ismeasured and tabulated keeping always constant.

6. The experiment is repeated for different values of collector to emittervoltage .

7. A graph is drawn with along the X axis and along the Y axis.8. This is the input characteristic of the transistor in common emitter

configuration for an output voltage 0 Volt.9. Input characteristic is drawn with constant output voltage 9V as well.10.The reciprocal of the slope of the characteristic gives the input resistance ri

of the transistor.

TO DRAW OUTPUT CHARACTERISTICS1. The output characteristic is a graph connecting output current and output

voltage

for a constant input current

.

2. The base current IB is fixed at 0A by using potentiometer P1.3. The collector to emitter voltage is increased in step of say 0.5 volt.4. Value of collector current is noted and tabulated keeping always

constant.5. Above steps are repeated for different values of base current .6. A graph is drawn with along the Y axis and along the X axis.


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7. The reciprocal of the slope of the graph gives output resistance (r0).

TO DRAW TRANSFER CHARACTERISTICS1. This graph connects and for a constant .2. The output voltage is kept constant at 3V by adjusting the rheostat P2.3. The input current is varied from zero in step of 25A.4. The output current is noted.5. versus graph is plotted.6. This gives the transfer characteristic of the transistor.

The slope of the transfer characteristic gives the current gain ().

OBSERVATIONS:

Least count of voltmeter in input = .V.


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Least count of ammeter in input =mA.Least count of voltmeter in output = .V.Least count of ammeter in output =mA.

TO DRAW INPUT CHARACTERISTICS = 0V

A V

=3V

A V

TO DRAW OUTPUT CHARACTERISTICS

IB25A

V mA

IB50A

V mA

IB75A V

mAIB

100A

V mA

TO DRAW TRANSFER CHARACTERISTICS

3V

A

mA


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The static characteristic of a transistor are drawn.

The Input resistance = =

The output resistance= ..

The current gain of the transistor = = .

RESULT:

The static characteristic of a transistor are drawn.

The Input resistance =

The output resistance=..

The current gain of the transistor = .


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EXPERIMENT III

GRATING NORMAL INCIDENCE

AIM: To standardise the grating using the green line of the mercury spectrum andhence to determine the wavelength of the other prominent lines of mercuryspectrum by the normal incidence method.APPARATUS:

Spectrometer, The given grating, mercury vapour lamp etc.

PRINCIPLE:

At normal incidence,sin

=

where,

= the angle of diffractionN = the number of lines per meter of the gratingN =the order of the spectrum and = the wavelength of light used in meter.

If of green line is known, N can be calculated, ie the grating can be

standardised.

=

Having found the value of N, the wavelength of the other prominent linescan be determined using the formula,

= PROCEDURE:Preliminary adjustments of the spectrometer are done:I.Focussing of the eye - piece

1.The telescope is turned towards a white wall.2.The eyepiece is gently pushed in or pulled out until the cross- wires are

clearly seen.II.Adjustments of telescope

1.The telescope is turned towards a distant object.2.The rack and pinion arrangement on it, the telescope is adjusted to get a

clear image of the distant object at the cross- wires, without parallax.3.The telescope is now ready to receive parallel rays.


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III.Adjustment of collimator

1.The slit of the collimator is opened slightly.2.The slit is illuminated with light from a mercury lamp.3.The telescope is then brought in line with the collimator.4.The image of the slit is observed through the telescope.5.Looking through the telescope, the rack and pinion arrangement of the

collimator is adjusted so that a well defined image of the slit is obtained atthe cross wires.

IV.Levelling of the prism table

1.The prism table can be leveled looking through the telescope.2.The grating is fixed on the table, telescope is arranged to get the reflected

image from grating.3.The screws are adjusted so that the vertical cross wire bisects the reflected

image.

V.To arrange the grating for normal incidence1.The preliminary adjustments of the spectrometer are made.2.The slit is made narrow.3.The telescope is brought in line with the collimator.4.The telescope is adjusted so that the point of intersection of the cross wires

coincides with the fixed edge of the image of the slit.5.The telescope is then clamped.6. The vernier table is unclamped and adjusted so that the reading of vernier

I is 00 and the reading of vernier II is 1800 .7.The vernier table is then clamped. The telescope is then unclamped and

rotated exactly through 900 and then clamped.8.The grating is then mounted on the grating table with its ruled surface

facing the collimator.9.The grating table alone is rotated so that the reflected image of the slit

coincides with the point of intersection of the cross wires.10.The reflected image will be white in colour. (There may be two reflected

images. The brighter one is chosen.) Now the angle of incidence is 450 .


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11.The vernier table is now unclamped and rotated exactly through 450 insuch a direction that the ruled surface of the grating faces the collimator.

12.The vernier table is then clamped. The grating is now in the normalincidence position.

VI.To standardize the grating

1. The telescope is unclamped and brought in the line with the collimator.2. The direct image of the slit is observed.3. The telescope is slowly rotated towards left.4. The first order spectrum of mercury light is observed.5. The telescope is adjusted so that the cross wire coincides with the green

line.6. The readings of vernier I and vernier II are noted.7. The telescope is then rotated to the right of the direct image and adjusted

so that the cross wire coincides with the green line of the first orderspectrum in the right.8.The readings of vernier I and vernier II are noted.9.The difference in readings of the corresponding verniers on the left andright sides is determined.10. The average value of the difference gives 2. Then angle of diffractionfor the first order green line g is found.11.The wavelength of green line, g, the number of rulings per meter, N ofthe grating is calculated using the formula,

= where n =1 for the first order image.


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VII.To determine the wavelengths of the other lines

1. The angles of diffraction for the different lines in the first order spectrumare determined as before.

2. The corresponding wavelengths are calculated using the formula, = where n=1 for first order.OBSERVATIONS:

Adjustments for normal incidence

Vernier I Vernier I

Direct Reading .

Reading after the telescope is turned through 900 ..

Reading after rotating the vernier through 450

To standardize the grating to find N

Value of 1 m.s.d =degree

=.minutes

No.of divisions on the vernier n =

Least count of vernier =1 m.s.d/n=..

=minutes

Total Reading =Main Scale Reading +(Vernier Scale reading x LC)

Wavelength of mercury green g =5461 x10-10 m


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Determination of wavelengths

Order

n

Line

Vernier

Diffracted reading

Difference2

Mean

=sin/nN

Left Right

MSR VSR Total MSR VSR Total

1

Violet V1

V2

Blue V1

V2

Green V1

V2

Yellow I V1

V2

Yellow II V1

V2

RESULT:

The wavelengths of the prominent lines of the mercury spectrum are given in thetabular column.


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EXPERIMENT IV

GRATING - DIFFRACTION

AIM:

To study the relation between the sine of the angle of diffraction and the

wavelength of light.APPARATUS:

Spectrometer, grating, mercury vapour lamp etc.

PRINCIPLE:

At normal incidence,sin = where,

= the angle of diffractionN = the number of lines per meter of the grating

N =the order of the spectrum and = the wavelength of light used in meter.If of all the colour is known, N can be calculated, ie the grating can be

standadised.

= The value of N is found out in all the cases and found to be constant.

PROCEDURE:

1.The eye piece is adjusted.

2.Telescope is adjusted.3.Collimator is adjusted.4.Prism table is leveled.5.Grating is set for normal incidence.6. Grating is standardized with green light.

OBSERVATIONS:


Vernier I Vernier I

Direct Reading .

Reading after the telescope is turned through 900 .

Reading after rotating the vernier through 450 ..


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To standardize the grating to find N

Value of 1 msd =degree

=.minutesNo.of divisions on the vernier n =

Least count of vernier =1 msd/n=..

=minutes

Total Reading =Main Scale Reading +(Vernier Scale reading x LC)

Wavelength of mercury green g =5461 x10-10 m


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Determination of value of N

Order

n

Line ()Vernier

Diffracted reading

Difference

2

Mean

NLeft Right


1

Violet 4047V1

V2

Blue 4358V1

V2

Green 5461

V1

V2

Yellow I 5770V1

V2

Yellow II 5790V1

V2

Mean value of N=.

RESULT:

The value of N is found to be a constant.

The sine of angle of diffraction varies linearly with wavelength.


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EXPERIMENT V

VOLTAGE REGULATION USING ZENER DIODE

AIM:

To study the voltage regulation characteristic of a Zener diode and to plot its

line and load regulation characteristics.APPARATUS:

Zener diode (5.6V) , resistor(270 ) , rheostat(0 - 1.2K), voltmeter(0-10V) , milliammeter(0-100mA),DC voltage source(30 Volt).PRINCIPLE:

A Zener diode is operated in the reverse breakdown region in a circuit. ThenZener voltage (V) remains almost constant irrespective of current through it ().A series resistor () is used to limit the Zener current to less than its maximumcurrent rating. The current in the series resistor () is given by the relation

= + (1)where is the current through the load resistor.(). The values of and are given by the expressions.

R = =

... (2)

R =()

() ..... (3)where Vi(mini) is the minimum value of input voltage and IL(max) is the maximumvalue of current through load resistor.

PROCEDURE:

The circuit diagram is made as shown in the figure below:


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LINE REGULATION GRAPH1.The input voltage (V) is adjusted to be 10 Volt.2.The load resistance is adjusted so that the milliammeter indicates 10mA.3.The load resistance is kept at this value.4.The input voltage varied from 7 Volts to 10 Volts in equal steps of 0.5Volt.5.A graph is plotted with Valong X- axis and V along Y- axis.6.It is called line regulation graph and in as shown in figure below:

Again keep the input voltage constant (say V = 10V) by adjusting thepotential divider in the input supply.

LOAD REGULATION GRAPH1.The load resistance is varied so that the load current (I) increases from 2

to 12mA in equal steps.2.In each step the output voltage (V) is noted.3.A graph with Ialong X axis and V along Y axis.4.It is called load regulation graph and is shown in figure below:


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OBSERVATION:

LINE REGULATIONI= 10mA

LOAD REGULATIONV= 10V

RESULT:

Line regulation graph is drawn.

Load regulation graph is drawn.

V VV V

I VmA V


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EXPERIMENT VI

NEWTONS RINGS

AIM:

To determine the radius of curvature of a convex lens by Newtons Rings

method.APPARATUS:

Newtons rings apparatus, sodium vapour lamp, vernier microscope, aconvex lens of large focal length(about 1 m) etc.PRINCIPLE:

The diameter of the nth dark ring is given by,Dn

2= 4nR(1)where R is the radius of curvature of the lower surface of the convex lens and is

the wavelength of light used.The diameter of the (n+k)th dark ring is given by

Dn+k2 = 4(n+k)R .(2)Then Dn+k

2 - Dn2=4kR

R= Dn+k2 - Dn

2/ 4k..(3)

PROCEDURE:


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1. The Newtons ring apparatus consists of an optically plane glass plateG on which a long-focus convex lens L is placed.

2. There is a glass plate P inclined at 450 to the horizontal.3. Light from a sodium lamp is rendered parallel by a short focus convex

lens L1.

4. These parallel rays fall on the glass plate P and get reflected verticallydownward and fall on the system of the lens L and the glass plate G.

5. The light reflected from the lower surface of the lens L and the uppersurface of the glass plate G interfere and a number of concentric dark and

bright rings formed.6. These rings are observed through a microscope arranged vertically above

the glass-plate P.7. The microscope is focused well so that the rings are clearly seen.8. The center of the ring system is dark.9. Then by working the tangential screw, the point of intersection of thecross-wire is kept at the central dark spot.10.Then the microscope is moved to the left and to the right in order to

ensure that about 25 dark rings are clearly seen.11.Then again starting from the central dark spot, the microscope is moved

to the left by working the tangential screw so that the cross-wire istangential to the 22nd dark ring on the left.

12.The tangential screw is then slowly adjusted so that the cross-wire istangential to the 20th dark ring.

13.The microscope reading on the horizontal scale is taken.14.Then by working the tangential screw the cross wire is kept tangential to

the 18th, 16th,14th, etc., dark ring up to the second dark ring on the left andthe reading corresponding to each ring is taken.

15.Then by working the tangential screw, the microscope is moved in thesame direction until the cross wire is tangential to the second dark ring onthe right.

16.The corresponding reading is taken. Similarly the cross-wire is kepttangential to the 4th ,6th,8th,etc., dark rings up to the 20th dark ring on theright. The reading corresponding to each ring is taken.

17.(The tangential screw should be worked only in one direction from theposition of the 20th ring on the left to the position of the 20th ring on theright. This is to avoid back lash error)

18.The difference in readings on the left and right of each ring gives itsdiameter D.

19. The value of D2 is calculated. The values of Dn+k2 Dn

2 are calculated,for a value of k=10. Then the mean value of (Dn+k

2 Dn2 ) is found.


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20.If the wavelength of sodium light is , the radius of curvature of the

convex lens for the marked surface can be determined using the equationR= Dn+k

2 Dn2

/ 4k where k=10

OBSERVATIONS:

Microscope readings

Value of 1 msd =..cm

No. of divisions on the vernier n= .

Least Count(LC) = 1msd/n =cm

Wavelength of monochromatic light = 5893


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Orderofthering

Microscope Reading

Diameter(D

)

D2

Dn+k

2

Dn2

Left Right

MSR(x)

VSR(y)

TOTALX+(yxLC)

MSR(x)

VSR(y)

TOTALX+(yxL

C)

cm div cm cm div cm cm cm2 cm2

2018161412

10864

2

Mean value of Dn+k2 Dn

2 = m2

Radius of curvature of the surface of the lens R= Dn+k2 Dn

2/4k (here k=10)

R=m

RESULT:

Radius of curvature of the convex lens R=..m


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EXPERIMENT VII

CHARACTERISTICS OF PHOTODIODE

AIM:

To draw the characteristic of a photo diode.APPARATUS:

D.C. power supply (0-10V), Photo diode, mercury lamp, voltmeter (0-10V),digital multimeter, resistors.PRINCIPLE:

If the photodiode is forward biased, then the amount of current flowingthrough it may be very large. Additional current due to photo effect may not bedominant. When the junction is reverse biased, the original current is very small.Under this condition if the diode is exposed to light, then an appreciable increase inthe reverse current is observed.

PROCEDURE:The circuit is completed as shown in the diagram.

1.The connections are done as per the circuit diagram given above.2.Characteristics of the photo diode is found out by keeping diode in cover.

3.The diode is covered to protect it from light. The current in the circuit is foundout for various values of voltages starting from 0V to 1.4V.4.The experiment is repeated by exposing the photo diode to mercury lamp.5.A graph is plotted with voltage along X axis and current along Y axis.


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OBSERVATION:

Position of thephoto diode

VR IR

V mA

Covered tolight

00.20.40.60.81.01.2

Exposed tomercury lamp

00.2

0.40.60.81.01.2

RESULT:

Characteristic of curve (volt-ampere) of the photo diode is drawn.


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EXPERIMENT VIII

CHARACTERISTICS OF LEDAIM:

To study the characteristic of Light Emitting Diode (LED)APPARATUS:

LED, 200 resistor, D.C. power supply (10V), milli ammeter (0 50mA),voltmeter (0 10V)PRINCIPLE:

A light emitting diode (LED) is a semiconducting p-n junction device whichproduces light energy when it is forward biased. At the forward biased state, theelectrons from the n region and the holes from the p region recombine at theinterspace releasing light energy. This property is called electro luminescence.There is a transition of electrons from the conduction band to the valance band

where they combine with holes emitting photons. The holes thus created in the nregion also combine with electrons releasing photons. The energy of the photonemitted in the electron volts is given by

= = where is frequency of photon emitted, is the wavelength of photon and c is thevelocity of light.

LED is usually made up of gallium phosphide (GaP) and gallium arsenidephosphide (GaAsP).


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PROCEDURE:

1. An LED is connected in series with a battery, a resistor R (200) amilliammeter (0-50 mA) and rheostat (500).

2. A voltmeter V (0 10 volts) is used to measure the p.d. applied.3. LED is forward biased and the battery is switched on.4. The voltage is varied in small steps and in each step, current is noted

from the milliammeter.5. The readings are recorded.6. A graph is plotted with voltage on X - axis and current on Y- axis .7. The curve obtained is the characteristic of LED and it is similar to the

characteristic of a forward p-n junction.

The voltage V at which conduction just begins can be noted from thischaracteristic.

OBSERVATIONS:

Least count of ammeter = .mA

Least count of voltmeter=..V


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VoltmeterReading

AmmeterReading

V mA

Charge of an electron e = 1.6 x10-19 coulombs

Voltage at which conduction begins V = ..Volts.Energy of photon Emitted, E = eV =

Wavelength = =

RESULT:

Characteristic of LED drawn.

Wavelength of light = .


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EXPERIMENT IX

GRATING - DISPERSIVE POWER

AIM:

To determine the dispersive power of a plane transmission grating arranged

for normal incidence.APPARATUS:

Spectrometer, grating, mercury vapour lamp etc.PRINCIPLE:

The dispersive power of a grating is the ratio of change in angle ofdiffraction to the corresponding change in wavelength of any two neighbouringlines. Let two wavelengths and +d be diffracted through and +d.

Dispersive power of grating =

PROCEDURE:

1.The eyepiece is focused.2.Telescope is adjusted.3.Collimator is adjusted.4.Prism table is leveled.5.Grating is set for normal incidence.6. Grating is standardized with green light.

To find dispersive power

1.The spectrometer is now set up for normal incidence of light from a

mercury lamp.2.Telescope is brought in a line with the collimator to observe the directimage.

3.It is turned to either side of the direct image to observe the diffractedspectrum in the first order.

4.The vertical crosswire is adjusted to coincide with the lines, green, yellowI and yellow II successively on the left side.

5.The reading for each line both in vernier I and vernier II are noted.6.Now the telescope is turned to the right side of the direct image and

vertical crosswire is adjusted to coincide with the lines successively.

7.The readings for each line in both the verniers are taken.8.The difference between the readings in corresponding verniers on the left

and the right side gives 2.

9.Mean angle of diffraction for each line is calculated.10.For a Grating , sin =


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11.For first order (n=1), knowing wavelength of green line (g =5460X10-10

m), the number of lines per metre of grating (N) is calculated from

= where g is the angle of diffraction.12.Wavelength for yellow I and yellow II lines are calculated from the

above equation sin = .13.Dispersive power

for yellow region is calculated as follows 1 is the

angle of diffraction for yellow I whose wavelength is 1 .14. Similarly 2 is the angle of diffraction for yellow II whose wavelength

2.d = 1 - 2 and d =1 - 2

is determined.

OBSERVATIONS:


Vernier I Vernier II

Direct reading ...............

Reading which telescope is turned through 900 ..

Reading when vernier table is turned through450 .

To find the least count (l.c)

Value of 1 main scale division= .minute

No.of vernier scale division n=

Least Count(L.C)=1msd/n =..minute

Total reading=Main Scale Reading +(Vernier scale Reading x LC)


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To determine wavelength of lines

Order

Line

Vern

ier

Diffracted reading

Differenc

e2

Mean

=sin/n

NLeft Right


GreenV1

V2

Yellow IV1

V2

Yellow II

V1

V2

To calibrate the grating

Wavelength of green g =5460 x10-10 m

Angle of diffraction g = ..

Order of the spectrum n=1

Number of lines/m, = =.

Dispersive power for yellow region

For Yellow I

Angle of diffraction 1 =.

Wavelength 1 =


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For Yellow II

Angle of diffraction 2 =.

Wavelength 2=

d=1 - 2 = .. = radian

d=1 - 2 =..

Dispersive power=..radian/m

RESULT:

Dispersive power of grating in Yellow region =..radian/m


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EXPERIMENT X

GRATING- RESOLVING POWER

AIM:

To determine the resolving power of a plane transmission grating using

spectrometer arranged for normal incidence.APPARATUS:

Spectrometer, given grating, mercury vapour lamp etc.PRINCIPLE:

Resolving power of a grating is its ability to show two neighbouring spectrallines in a spectrum as separate. If and +dare wavelengths of two neighbouring

spectral lines, the resolving power of the grating is the ratio.

PROCEDURE:

1. The preliminary adjustments of the spectrometer ie eye-piece adjustment,telescope adjustment and collimator adjustment are done .

2. The spectrometer is now set up for normal incidence of light from amercury lamp.

3. Telescope is brought in a line with the collimator to observe the directimage.

4. It is turned to either side of the direct image to observe the diffractedspectrum in the first order.

5. The vertical cross wire is adjusted to coincide with the lines green,yellow I and yellow II successively on the left side.6. The readings for each line both in vernier I and vernier II are noted.

7. The telescope is turned to the right side of the direct image and verticalcrosswire is adjusted to coincide with the lines successively.

8. The readings for each line in both the verniers are taken. The differencebetween the readings in corresponding verniers on the left and right sidegives 2.

9. Mean angle of diffraction for each line is calculated. Grating isstandardized as follows.

10.For a grating, sin=Nn. For first order (n=1), knowing wavelength ofgreen line (g=5460 x10-10m) , the number of lines per meter of thegrating (N) is calculated from = where g is the angle ofdiffraction.

11.Wave length for each line is calculated from the above equationsin=Nn.


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From the values the resolving power of the spectrometer is calculated.

OBSERVATIONS:

Adjustment for normal incidence

Vernier I Vernier II

Direct Reading .. ..

Reading when telescope is turned through 900 ..

Reading when vernier table is turned through 450 ................ .

To find the least count

Value of 1 main scale division =..minute

No. of vernier scale division n=..

Least Count(L.C) =1 msd/n =..minute

Total Reading =Main Scale Reading +(Vernier Scale Reading x LC)

To calibrate the grating

Wavelength of green g =5460x10-10m

Angle of diffraction g = .

Order of the spectrum n=1

Number of lines /m,

=

=.


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To determine wavelength of lines

Order

Line

Vernier Diffracted reading

Differnce2

Mean

=sin/Nn

Left Right

1


Green

V1

V2

Yellow

I

V1

V2

Yellow

II

V1

V2

To calculate resolving power of grating

Wavelength of Yellow I, 1 =Wavelength of Yellow II ,2 =Mean wavelength =1+2/2 =Change in wavelength d =2 - 1 =..Resolving power /d= ..

RESULT:

Resolving power of the given grating = ..


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EXPERIMENT XI

AIR WEDGE

AIM:To determine the diameter of a thin wire by measuring the width of the

interference bands formed by the air wedge arrangement and also the angle ofwedge.APPARATUS:

Two optically plane rectangular glass plates, the given wire, sodium vapourlamp, travelling microscope etc.(Air wedge is formed by placing two optically plane glass plates one above theother and keep the wire in between the plates. One end of the plates is held tight bya rubber band so that it becomes the line of contact and put another rubber bandloosely on the other end so that it forms the open edge).THEORY

The diameter of the wire used to form the air wedge is given by = where l is the distance of the wire from the edge at which plates are in contact(tight end), the wave length of light used and the band width.PROCEDURE:

1.Light from the sodium lamp is rendered parallel by a short focus convexlens(lamp should be placed at a large distance) and is allowed to fall on aglass plate inclined at 450 to the horizontal(fig1).

2.Place the air wedge such that light reflected from the glass plate B isincident normally on the air wedge.

3.Adjust the travelling microscope which is placed vertically above theglass plate B to view clearly the interference bands.

4.(Bands are formed by the light reflected from the top and bottom surfacesof air film enclosed between the two glass plates of air wedge.) Using thetangential screw, one of the cross wires is made to coincide with a dark

band.5.Count the number of clear bands obtained (20 or above) so that tangential

screw is free to move on either side.6.Make the cross wire to coincide with a dark band either on extreme right

or extreme left and take the reading on the horizontal scale.7.(Reading =MSR+VSR x LC). Move the cross wire to n+2

th,n+4th,n+18th band and note the microscope readings in eachcase.


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8.From these readings width of 10 bands is calculated (X) andband width is also found (X/10).

9.Distance l between the wire and line of contact of the plates ismeasured. Knowing the wavelength of sodium light (589.3nm) diameterof the wire is calculated.

OBSERVATIONS:

Value of 1 main scale division = .cm

Number of divisions on the vernier n=.

L.C. of microscope = 1 msd/n =cm


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Numberof bands

Microscope Readings Width of 10bands Xcms

MeanXcms

Bandwidth=mean

X/10 cmsMSR VSR Total=MSR+VSRx LC

nn+2n+4n+6n+8

X0X2X4X6X8

nn+10n+12n+14

n+16n+18

X10X12X14X16

X18

X10 - X0X12 - X2X14 - X4X16 - X6

X18 - X8

Distance of wire from the line of contact of the plates l=..cm

Wavelength of sodium light =589.3nm

Diameter of the wire

=

radians

Angle of wedge = radians

RESULTS:

Diameter of the wire = m

Angle of wedge = .radians


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EXPERIMENT XII

MELDES EXPERIMENT

AIM:

To determine the frequency of a tuning fork by Meldes arrangement, using

the transverse mode of vibration and using the longitudinal mode of vibrationAPPARATUS:

Electrically maintained tuning fork, fine thread, scale pan, weight box,balance etc.

The arrangement consists of an electrically maintained tuning fork. One endof a string is attached to one of the prongs of the fork. The other end of the stringcarrying a scale pan is passed over a pulley.PRINCIPLE:

Transverse mode of vibration

The frequency n of the fork is calculated using the formula

= .(1)

Longitudinal mode of vibration

= .(2)

where m= linear density of stringM= total mass at the end of the stringl= average length of one loopg=acceleration due to gravity

PROCEDURE:

Zero resting point ()1.The balance is gently released. Five successive turning points, starting

from the left are taken.2.The average of the three turning points on the left and the average of the

two turning points on the right are found.3.The average of these two averages gives the zero resting point ()of the

balance.Sensibility (S) of the loaded balance and mass of the body

1.The body is placed in the left pan. Sufficient weights are placed in theright pan so that the pointer swings almost equally to both sides.


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2. Let the total weight in the right pan be W. The resting point () isdetermined.

3. If is greater than, a weight of 10mgm is added to the right pan. (If is less than, 10mgm is removed). The resting point is again found.4. Let it be ( It is preferably to have and lying on either side of).5.The change in R.P due to 10mg = ( ).6.Sensibility of the loaded balance=

() /

= .() /

7.Then the correct weight of the body = + ( ) . Thus thecorrect weight of the body is determined.

8.The weights of the 10m thread and pan are determined.

Transverse mode of vibration1.The mass of the scale pan is determined correct to a milligram.2.10 meters of the given string is weighed accurately. Hence its linear density

(mass per unit length), m is found.3.The electrical connections are made as shown in the diagram.4.The string is arranged horizontally with its length parallel to the prong of the

fork.5.The fork vibrates in a direction perpendicular to the length of the string.6.A mass of about 2 or 3 gm is placed in the scale pan.

7.The circuit is closed.8.The fork vibrates.9.Transverse stationary waves are formed in the string.10.The length of the string between the prong and the pulley is carefully

adjusted by moving the fork, so that a number of well defined loops areformed in the string.

11.Leaving the loops at the two ends, the length of a definite number of loopsare measured. Then

12.The average length of a loop is found (l). The total mass M at the end ofthe string (mass of scale pan + mass placed in the pan) is noted. The valueof M/l2 is found.

13.The experiment is repeated for different masses in the scale pan and themean value of M/l2 is calculated.

14.Then the frequency of the fork is calculated using the formula,

= .(1)


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Longitudinal mode of vibration

1.The apparatus is arranged as shown in the diagram, with theprongs perpendicular to the string.

2.Then the fork vibrates in a direction parallel to the string or stringvibration in the longitudinal mode.

3.The experiment is performed exactly as before for differentmasses and the mean value of M/l2 is found.

4.The frequency of the fork is calculated using the formula,

=


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OBSERVATIONS:

Load in the pans Turningpoints

Restingpoint

Sensibility = 0.01

( )Correctwt

+ ( )Left Right Left Right

Nil Nil =

Scalepane

W =

W+0.01gm

=

10meterlength

ofstring

=

=

Length of the string = m

Mass of the string = .gm = ..kg.

Linear Density m = ..kg/m

Mass of scale pan = .gm = .kg

Accelaration due to gravity, g = 9.8 ms-2


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Transverse Mode

Trial NoMass inthe scale

pan

Totalmass

includingthe massof pan(M)

Numberof loops

X

Lengthof Xloops

L

Lengthof oneloop

l=L/X

M/l2

g 10-3kg cm cm Kg/m2

1

2

3

4

5

Mean M/l2 =

Frequency of the fork, =

=Hertz


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Longitudinal Mode

Trial NoMass inthe scale

pan

Totalmass

includingthe massof pan(M)

Numberof loops

X

Length

of Xloops

L

Length

of oneloop

l=L/X

M/l2

g 10-3kg cm cm Kg/m2

1

2

3

4

5

Mean M/l2 =

The frequency of the fork = =Hertz

RESULT:

The mean frequency of the fork =Hz

experiments 26.11

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