View
222
Download
0
Category
Preview:
Citation preview
7/28/2019 Experiments 26.11
1/46
1
SREEPATHY
INSTITUTE OF
MANAGEMENT
ANDTECHNOLOGY
Vavannoor, Palakkad District
LAB MANUAL
EN 09 103 P ENGINEERING PHYSICS
7/28/2019 Experiments 26.11
2/46
2
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
7/28/2019 Experiments 26.11
3/46
3
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.
7/28/2019 Experiments 26.11
4/46
4
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.
7/28/2019 Experiments 26.11
5/46
5
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.
7/28/2019 Experiments 26.11
6/46
6
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.
7/28/2019 Experiments 26.11
7/46
7
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.
7/28/2019 Experiments 26.11
8/46
8
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.
7/28/2019 Experiments 26.11
9/46
9
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
7/28/2019 Experiments 26.11
10/46
10
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 = .
7/28/2019 Experiments 26.11
11/46
11
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 eye- piece 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.
7/28/2019 Experiments 26.11
12/46
12
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 .
7/28/2019 Experiments 26.11
13/46
13
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.
7/28/2019 Experiments 26.11
14/46
14
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
7/28/2019 Experiments 26.11
15/46
15
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.
7/28/2019 Experiments 26.11
16/46
16
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:
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 ..
7/28/2019 Experiments 26.11
17/46
17
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
7/28/2019 Experiments 26.11
18/46
18
Determination of value of N
Order
n
Line ()Vernier
Diffracted reading
Difference
2
Mean
NLeft Right
MSR VSR Total MSR VSR Total
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.
7/28/2019 Experiments 26.11
19/46
19
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:
7/28/2019 Experiments 26.11
20/46
20
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:
7/28/2019 Experiments 26.11
21/46
21
OBSERVATION:
LINE REGULATIONI= 10mA
LOAD REGULATIONV= 10V
RESULT:
Line regulation graph is drawn.
Load regulation graph is drawn.
V VV V
I VmA V
7/28/2019 Experiments 26.11
22/46
22
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:
7/28/2019 Experiments 26.11
23/46
23
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.
7/28/2019 Experiments 26.11
24/46
24
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
7/28/2019 Experiments 26.11
25/46
25
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
7/28/2019 Experiments 26.11
26/46
26
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.
7/28/2019 Experiments 26.11
27/46
27
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.
7/28/2019 Experiments 26.11
28/46
28
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).
7/28/2019 Experiments 26.11
29/46
29
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
7/28/2019 Experiments 26.11
30/46
30
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 = .
7/28/2019 Experiments 26.11
31/46
31
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 =
7/28/2019 Experiments 26.11
32/46
32
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:
Adjustments for normal incidence
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)
7/28/2019 Experiments 26.11
33/46
33
To determine wavelength of lines
Order
Line
Vern
ier
Diffracted reading
Differenc
e2
Mean
=sin/n
NLeft Right
MSR VSR Total MSR VSR Total
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 =
7/28/2019 Experiments 26.11
34/46
34
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
7/28/2019 Experiments 26.11
35/46
35
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.
7/28/2019 Experiments 26.11
36/46
36
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,
=
=.
7/28/2019 Experiments 26.11
37/46
37
To determine wavelength of lines
Order
Line
Vernier Diffracted reading
Differnce2
Mean
=sin/Nn
Left Right
1
MSR VSR Total MSR VSR Total
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 = ..
7/28/2019 Experiments 26.11
38/46
38
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.
7/28/2019 Experiments 26.11
39/46
39
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
7/28/2019 Experiments 26.11
40/46
40
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
7/28/2019 Experiments 26.11
41/46
41
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.
7/28/2019 Experiments 26.11
42/46
42
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)
7/28/2019 Experiments 26.11
43/46
43
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,
=
7/28/2019 Experiments 26.11
44/46
44
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
7/28/2019 Experiments 26.11
45/46
45
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
7/28/2019 Experiments 26.11
46/46
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
Recommended