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Humanities & Sciences Engineering Physics Lab
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INSTRUCTIONS FOR LABORATORY
1) The objective of the laboratory is learning. The experiments are designed to
illustrate phenomena in different areas of Physics and to expose you to
measuring instruments. Conduct the experiments with interest and an attitude
of learning.
2) You need to come well prepared for the experiment
3) Work quietly and carefully (the whole purpose of experimentation is to make
reliable measurements!) and equally share the work with your partners.
4) Be honest in recording and representing your data. Never make up readings or
doctor them to get a better fit for a graph. If a particular reading appears wrong
repeat the measurement carefully. In any event all the data recorded in the
tables have to be faithfully displayed on the graph.
5) All presentations of data, tables and graphs calculations should be neatly and
carefully done.
6) Bring necessary graph papers for each of experiment. Learn to optimize on
usage of graph papers.
7) Graphs should be neatly drawn with pencil. Always label graphs and the axes
and display units.
8) If you finish early, spend the remaining time to complete the calculations and
drawing graphs. Come equipped with calculator, scales, pencils etc.
9) Do not fiddle idly with apparatus. Handle instruments with care. Report any
breakage to the Instructor. Return all the equipment you have signed out for
the purpose of your experiment.
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Vision:
To emerge as a destination for higher education by
transforming learners into achievers by creating, encouraging
and thus building a supportive academic environment.
Mission:
To impart Quality Technical Education and to undertake
Research and Development with a focus on application and
innovation which offers an appropriate solution to the
emerging societal needs by making the students globally
competitive, morally valuable and socially responsible citizens.
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CONTENTS
S.No. Experiment Page no.
1 Determination of Rigidity modulus of
a material – Torsional pendulum
5
2 Melde’s Experiment – Transverse and
Longitudinal Modes
9
3 Time Constant of RC Circuit 13
4 Diffraction Grating using LASER 17
5 Resonance in LCR circuit 21
6 Optical fiber-Numerical Aperture&
Bending Losses
25
7 Characteristics of LED 29
8 Characteristics of Solar Cell and to
Determine the Fill Factor
33
9 Energy gap of a material of p-n
junction
37
10 Magnetic field along the axis of a coil
(Stewart & Gees method)
41
11 Dispersive Power of the material of a
Prism – Spectrometer
45
12 Newton’s Rings
49
13 Diffraction Grating 53
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1. Torsional Pendulum
AIM:
To determine the rigidity modulus (η) of the given wire using a Torsional
pendulum.
Apparatus:
Torsional Pendulum, steel wire, stopwatch, meter scale, screw gauge, Vernier
calipers.
Principle:
Rigidity Modulus: η =
)dynes/cm
2
M - Mass of the disc.(gm)
R - Radius of the disc.(cm)
a - Radius of the wire.(cm)
l - Length of the pendulum.(cm)
T - Time period.(sec)
Arrangement:
Graph: A graph is drawn between length of the pendulum on X- axis and T2 on
Y- axis.
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Procedure:
The circular metal disc is suspended by steel wire as shown in the fig. The
length of the wire between the chuck nuts is adjusted to 100cm.A small mark is made
on the curved edge of the disc. The disc is set to oscillate by slow by turning the disc
through a small angle. There should be no lateral movement of the disc.
When the disc is oscillating the time taken for 20 oscillations is noted with the
help of a stop watch and recorded in the observation table as trial1. This procedure is
repeated for the same length and noted as trial2 in the observation table and mean
value is obtained from the trail1&trail2, calculate the time period(T).The above
procedure is repeated for the lengths 90,80,70&60cm and noted in the observation
table and time period(T) is calculated ie. Time for one oscillation.
The radius of the wire (a) is noted with the help of the screw gauge and
readings are recorded in the observation table and mean radius of the wire (a) is
calculated. Similarly the radius of disc is noted with the help of vernier calipers and
recorded in the observation table and mean radius of the disc is calculated.
A graph is drawn between the „l‟ on the x-axis and T2 on the y-axis.
value is
calculated from the graph .The rigidity modulus (η) is calculated by substituting the
observations in the formula.
Observations:
Mass of the disc (M) = gms
To determine the radius of the disc:
Least count of the Vernier calipers:-
S.No Main scale
reading(a)
Vernier
coincidence
Vernier
Reading(b)=(L.C*V.C)
Diameter of
disc=(a+b)
1
2
Mean diameter, d =__________________cms
Radius of the disc (R) =
d/2=______________cms
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To determine the radius of the wire:
Least count of the Screw Gauge:-
Screw Gauge Error:-
S.No P.S.R
(a) H.S.R
Corrected
H.S.R
H.S.R
(b=L.C*H.S.C)
Diameter of wire =
(a+b)
1
2
Mean diameter,x = ____________________mm
Radius of the wire (a)=x/2= ____________mm=____________cms
Time Period of the Pendulum:
S.N
o
Lengt
h of
the
wire
‟l‟(cm
)
Time taken for 10 oscillations Time for
1oscillatio
n
T=
(Sec)
T2
Trail1(Sec
)
Trail2(Sec
)
Average(t)(Sec
)
1
2
3
4
5
100
90
80
70
60
Average,
_=__________
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Precautions:
1. While using Vernier calipers see that the readings must be taken without any
parallax error
2. Measure the thickness of wire using screw gauge
3. Note the disc should be rotated along its own axis.
Calculations:
Result:
The rigidity modulus ( of the given wire is ____________________.
The rigidity modulus ( of the given wire from graph is
____________________.
Viva Questions:
1. What is the Time period (T)?
2. What is the formula for least count of the screw gauge and Vernier calipers?
3. Define the stress &strain?
4. Define the rigidity modulus?
5. Does the rigidity modulus depend upon the thickness of wire. How?
6. On what factor the periodic time depends?
7. What are the different types of elastic moduli?
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2. MELDE’S EXPERIMENT
AIM:
To determine the frequency of a vibrating bar (or) tuning fork using Melde‟s
arrangement.
Apparatus:
Melde‟s arrangement, connecting wires, meter scale, thread, weight box,
power supply.
Experimental arrangement:
Longitudinal mode:
Transverse mode:
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Principle:
In Longitudinal mode:
Frequency of tuning fork, n =
√
Hz
In Transverse mode:
Frequency of tuning fork, n =
√
Hz
Where,
µ - Mass per unit length (or) linear density =
(gm/cm)
T - Tension= (M+p) g. (dynes)
n- no. of loops
l – Length of „n‟ loop. (cm)
M-Mass in the Pan (gm)
p -Mass of the pan (gm)
Procedure:
Transverse mode:-
In transverse mode, the tuning fork is made to vibrate perpendicular to
vibrating thread, by adjusting the length of the thread and weights in the pan. The
thread starts vibrations and forms many well defined loops. These loops are due to
the stationary vibrations set up as a result of the superposition of the progressive
wave from the prong and the reflected wave from the pulley. The frequency of each
segment coincides with the frequency of the fork.
Set the Meld‟s experiment in transverse mode vibrations with1-2 meters
length of thread and note the number of loops. Repeat the same procedure for
different weights in the pan and record in the observation table and calculate the
frequency of the tuning fork.
Longitudinal mode:-
In longitudinal mode, the tuning fork is parallel to the vibrating thread. Set the
Meld‟s experiment in the longitudinal mode of vibrations and note the observations
in observation table for different weights. Calculate the frequency of the tuning fork
by using the formula.
Observations:
Mass of the thread (mt) -
Length of the thread (lt) -
Mass of the pan (p) -
Linear density µ= (
-
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Transverse mode vibrations:
S.No
Load applied in the
pan(M)gm
Tension
T=(M+p)g
(dynes)
No. of
loops
(n)
Length of the n
loops
(l)cm
ν=
√
(Hz)
Average, ν=
Longitudinal mode vibrations:
S.No
Load applied in the
pan(M)gm
Tension
T=(M+p)g
(dynes)
No. of
loops
(n)
Length of the n
loops
(d)
ν=
√
(Hz)
Average, ν=
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PRECAUTIONS:
The thread should be uniform and inextensible.
Well defined loops should be obtained by adjusting the tension with milligram
weights.
Frictions in the pulley should be least possible
calculations:
RESULT:
Frequency of the tuning fork in longitudinal mode ____________Hz
Frequency of the tuning fork in Transverse mode ____________Hz
Viva Questions:
1. What types of waves are produced in a fork when it is excited?
2. What are a transverse wave and a longitudinal wave?
3. What is a stationary wave?
4. What are beats?
5. What are nodes and antinodes?
6. What is effect of temp in the frequency of the tuning fork?
7. Define frequency and resonance?
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3. R.C. CIRCUIT
Aim:
To study the charging and discharging of voltage in a circuit containing
resistance and capacitor and compare the experimental RC time constant with
theoretical RC time constant.
Apparatus:
RC trainer kit, connecting probes, split watch.
Principle:
The charging voltage across the capacitor is given
V= (1 – e -t/RC
)
The discharging voltage across the capacitor is given
V= - e -t/RC
When t=RC then V=0.36 Vο
Where
t – Time constant (sec)
R – Resistance (ohms)
C – Capacitance (farads)
Vο- Max Voltage (volts)
Formula:
Time constant ofRC circuit t =RC. (Sec)
Circuit diagram:
v v
R S
12-9V C v
R S
12-9V
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Graph:
Procedure:
This circuit is connected as shown in fig, taking one set of R and C values.
When switch is connected the circuit starts charging.
Discharging:
When the switch is disconnected, the charged capacitor will be discharged
with time. The decayed voltage across the capacitor is noted with 5sec time interval
upto 0voltage.The graph is drawn between the voltage across the capacitor and time
on x-axis. The time constant is calculated at 36% of maximum voltage across the
capacitor and compared with theoretical value (RC).
Observation:
R: _______ohms C: ________µF
S.no
Voltage
across
Capacitor
(volts)
Time
(Sec)
T=RC
Voltage(v)
o Time (sec)
0.36Vo
T=RC
Voltage(v)
o Time (sec) T=RC
Voltage(v)
o Time (sec)
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Calculations:
Result:
For R=………..
C=………..
Theoretical Value
Time Constant (T) = RC=
Practical value Time constant (T) from graph at Discharging =
Viva Questions:
1. What is an electrolyte Capacitor?
2. What is the aim of the experiment?
3. When the capacitor is fully charged, what will be the potential across the
resistor?
4. Units of the resistor, capacitor and inductance?
5. What will happen if the resistance of low value is connected in the circuit
6. State the factors affecting capacitor
7. How the time constant is calculated from the experiment?
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4. DIFFRACTION GRATTING USING LASER
Aim:
To determine the wavelength of the Laser source using a grating.
APPARATUS:
Grating, screen, Meter scale,drawing sheet and LASER source.
THEORY:
A plane diffraction grating is an optical device consisting of large number of
parallel slits of the same width (a) and separated by equal opaque space(b). For
manufacturing a diffraction grating, fine parallel lines are drawn on a glass plate very
closely by means of a diamond point. The number of lines drawn per inch is
mentioned on the diffraction grating by the manufacturer.
The slit separation d=a+b is known as the grating element.
If there are N lines per inch on the plane diffraction grating, then the grating
element is given by,
dN =1 inch
d=1/N inch=2.54/2500 cm (since 1inch=2.54cm)
The theory is similar to double slit case, except that, instead of just using two
slits, the light beam will pass through the multiple slits of the diffraction grating. By
measuring the angles at which the interference peaks or maxima occur, we can
determine the wave length of the laser light by knowing the grating element.
The condition for obtaining maxima for normal incidence of light on the
diffraction grating is given by,
d sin θ=nλ
Where λ is the wave length of the laser light and θ is the angle corresponding to the
order of diffraction n=0, 1, 2, 3, ……
Principle maximum corresponds to zeroth order of diffraction. On either side
of principle maximum, the diffraction patterns of higher orders will be observed as
shown in figure.
PRINCIPLE:
Wavelength of the Laser source is given by
λ =
Where, = diffraction angle
n = order of diffraction
N = no. of lines per cm on grating
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EXPERIMENTAL ARRANGEMENT:
PROCEDURE:
Keep the grating in front of the laser beam such that the light is incident
normally on it. When laser light falls on the grating, the diffraction pattern is
produced on the screen in the form of bright spots which are called maxima. The
central maximum along with other maxima which are formed on either side of it
symmetrically can be seen on the screen. The positions of these bright spots can be
recorded on the graph sheet which is attached on the screen. The bright spot next to
central maxima is called the first order maxima and the light next to first order is
called second order maxima and so on. Each of the maxima corresponds to a specific
diffraction angle θ which can be measured by trigonometry. The distance central
maxima to the first order on the left are to be noted as d1 and the distance from the
central maxima to the first order on the right side is to be noted as d2. Repeat the
experiment for higher orders of diffraction and tabulate readings. Measure the
distance between the grating and the screen and tabulate it as D.
Observation:
No. of lines per cm on grating, N=2500/2.54
Order
(n)
distance
between
grating and
the screen,
D(cm)
Distance from Central
Maximum
sin θ
=
√
λ =
(cm) d1 d2 Mean
d(cm)
θ
L Central
Maxima
First
Order
First
Order
Second
Order
Second
Order
Screen
Laser
Source
Y sin θ ≈
Y/L
Diffraction
grating
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RESULT:-
Wavelength of the LASER source is λ = ………………..c m = ………….A0.
Viva Questions:
1. What is diffraction grating?
2. What is grating constant?
3. What are the characteristics of laser light?
4. Define the resolving power of a grating?
5. Why do you change a grating with less number of lines in this
experiment?
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5. LCR CIRCUIT
Aim:
To draw the characteristics ofLCR series resonance circuit and to determine
the bandwidth and half power frequencies.
Apparatus:
LCR trainer kit, function generator, connecting wires.
Principle:
Resonant Frequencies of series circuit fS =
√ Hz
L – Inductance. (Henry)
C – Capacitance. (Farads)
R – Resistance. (Ohms)
The bandwidth of the circuit is defined as the difference in half power
frequencies
Bandwidth f = f2 – f1
These can be determined by drawing a half power line on the characteristic
curve at 70.7% of the resonant or maximum value on the curve.
Series Circuit:
Model graph:
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Procedure:
Series Resonance: The circuit is connected as shown in fig 1. Fixed amplitude of
voltage at all frequencies is applied to the circuit through a function generator by
changing the frequency in steps of 100Hz. The current in the circuit is noted. The
readings are tabulated in the table. A graph is drawn between frequency in x-axis and
current in y-axis. The shape of the curve is shown in the fig. The half power points
are noted on the curve at 70.7% of max current Io and bandwidth calculated by
difference of half power points.
Bandwidth
TABLE-1: Series ResonanceCircuit
C=……….nf
L=……….mH
S.NO FREQUENCY
(KHz)
CURRENT (μA)
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Calculations:
RESULT:
For a series Resonant Circuit:
The resonant frequency fs= …………………….Hz
Quality factor was calculated to be Q = ……………….
Viva Question
1. Parallel resonance circuit is rejecter circuit and series resonant circuit is an
accepter circuit. Explain. Why?
2. Explain the importance of the band width.
3. What is the physical significance of the LCR?
4. What happen when we tune “Radio or T.V.”?
5. Why does the series circuit give a power maximum at resonance while the
parallel circuit led to a power minimum?
6. What is role of the inductance in LCR circuit? What are the units of
inductance?
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6(a).Optical fiber-Numerical Aperture
Aim: To determine the Numerical aperture of the given optical fiber.
Apparatus: Optical fiber trainer module, optical fiber cables, NA jig.
Formula:
NA = sin∝ =
√
Acceptance angle = sin 𝑁𝐴
Proceedure: The experimental set up for the NA measurement is shown in figure.
1. One end of the optical fiber is connected to the power output of LED and
the other end of the optical fiber is connected to NA jig through the
connector.
2. The AC mains are switched ON. The light emitted by LED passes through
the optical fiber cables to the other end. The set P0 knob is adjusted such
that, maximum intensity is observed on the screen and it should not be
further disturbed.
3. A Screen with concentric circles of known diameter is moved along the
length of the NA jig to observe the circular spreading of light intensity on
the screen.
4. The screen is adjusted such that the first circle from the centre of the screen
is completely filled with the light. At this position the distance L from the
fiber end to the screen is noted on the NA jig.
5. The experiment is repeated for the subsequent circles from the centre of the
screen are completely filled with the light by adjusting the length along the
NA jig and the readings are tabulated.
DIAGRAM
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OBSERVATIONS:
Sl.No Distance of the
screen (L) mm
Diameter of the
circle (D) mm
NA =
√
Acceptance angle =
sin 𝑁𝐴
PRECAUTIONS:
1. Any circumstances don‟t look directly into the LASER beam.
2. Don‟t shine reflected LASER towards any one.
3. It is very important that the optical sources should be properly aligned with
the cable and the distance from the launched point and cable is properly
selected to ensure that the maximum amount of optical power is transferred to
the cable.
RESULT:
The Numerical aperture of the given optical fiber is …………..
VIVA QUESTIONS:
1. Define Numerical Aperture.
2. What is the principle of the optical fiber?
3. Define critical angle.
4. Define acceptance angle.
5. Define total internal reflection
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6(b). Optical fiber-Bending Losses
AIM: To determine the losses in optical fiber due to macro bending
APPARATUS: Optical fiber trainer module, optical fiber cables of different lengths,
mandrel, DMM.
FORMULAE: Loss is given by
10 log (vo/vo‟)
THEORY: Attenuation result primarily from absorption and scattering of light.
Attenuation also results from a number of effects like, fiber bending, fiber joints,
improper cleaving and also splicing due to axial displacement and mismatch of core
diameters of fibers. But here, we study the attenuation due to macro bending.
EXPERIMENTAL SETUP:
PROCEDURE: To determine the bending losses:
a) Connect one end of the 1m long optical fiber cable to the output end of the
LED and the other end to the photo detector. Switch the power
b) Turn the SET POknob clockwise a little. Insert the leads of the DMM at the
output terminals and then note the output voltage(vo) in the DMM
c) Without disturbing the set po knob, wind one turn of OFC on the mandrel and
measure the output (vo)‟, in the DMM.
d) Repeat the experiment with other cables.
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OBSERVATIONS:
S.NO OUTPUT WITHOUT
BENDING (vo)
OUTPUT WITH
BENDING (vo)‟
LOSS= 10 LOG
(vo/vo‟)
PRECAUTIONS:
1) Any circumstances do not look directly into the LASER beam
2) Do not shine reflected LASER light toward anyone.
3) It is very important that the optical sources should be properly aligned with
the cable and the distance from the launched point and cable is properly
selected to ensure that the maximum amount of optical power is transferred to
the cable.
RESULT: The bending losses in OFC is -----------------
VIVA QUESTIONS
1. How many types of losses are there in a optical fiber?
2. What is the principle of optical fiber
3. Define bending loss?
4. Why it is called optical fiber?
5. What are the units of losses?
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7. CHARACTERISTICS OF LED
Aim: To study the characteristics of light emitting diode.
Apparatus: LED trainer kit, connecting probes.
Circuit Diagram:
Introduction: LED‟s are semiconductor p-n junction that under proper forward
biased conditions. They can emit external spontaneous radiations in UV, Visible,
Infrared region of EM spectrum. Usually GaAs, GaP or SiC materials are used as
light emitting materials. They emit light only when external applied voltage is
operated in forward bias mode and above a minimum threshold value. The gain in
electrical potential energy delivered by this voltage is sufficient to force electron
flow out of n-type material, across the junction barrier, in to the p-type region.
The LED involves basically three processes
1. The first one is an excitation process in which electron –hole pair is generated.
2. Second process is recombination process in which the exited carriers are give
up their energy either through radiative or non radiative process.
3. The third process is extraction of emitted photons from the active region of
semiconductor to the observer.
Procedure:
1. The main component of the apparatus is circuit board containing LED‟s, each
with a different emission wave length. A particular LED can be connected to
the circuit as shown in figure.
2. The voltage is varied with the help of power supply which is externally
connected.
3. Turn the power supply on and very slowly increase the voltage until the LED
just starts to glow.
A
V
R
Vin
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4. Continuously monitor the current as function of voltage across the diode.
5. Plot a graph between V on X-axis and I on Y- axis
Observations:
S.NO VOLTAGE (volts) CURRENT (ma)
Model graph:
Precautions:
1. Make sure that the voltmeter is measuring the voltage across the LED only.
2. Increase the power supply very slowly until the LED just starts to glow.
3. Continuously monitor the current.
Result:
The I-V characteristics of LEDs are studied.
Viva questions:
I (mA)
V(volts)
V (volts)
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1. How does an LED emit light?
2. What is the difference between an ordinary diode and an LED?
3. Which type of materials is used to manufacture LED?
4. What are the applications of LED?
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8. SOLAR CELL CHARACTERISTICS
AIM:
To determine the characteristics of solar cell and fill factor
APPARATUS:
Solar cell trainer kit, Solar cell, Variable light source.
FORMULAE:
Fill factor, f=
Where, ImXVm----- maximum obtainable power
Isc- Short circuit current
Voc- Open Circuit Voltage
THEORY:
If the depletion of unbiased junction is illuminated, charge separation takes
place, resulting in forward bias on the junction. Such device having large area
junction very close to the surface is capable of delivering power and is known as
SOLAR CELL. The cell converts directly solar energy into electricity.
The Solar Cell radiation is proportional to the delivered power of cell. The
efficiency of a cell is expressed in terms of the electrical power output compared
with the power in the incident PhotonFlux. The efficiency of Solar Cell depends on
the fraction of light reflected from the surface and the fraction absorbed before
reaching the junction. Silicon is widely used for Solar Cells.
CIRCUIT DIAGRAM:
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GRAPH:
PROCEDURE:
1. Place solar cell directly in front of variable intensity light source, and connect
output of solar cell to trainer kit.
2. Now gradually increase the intensity of bulb and observe the output of solar
cell on the voltmeter.
3. Connect the circuit as per circuit sketched below.
4. Vary the intensity of light, and note voltage and current in the meters
respectively and as well as the connected load.
5. Plot graph, between voltage and current at different intensities with and
without load.
OBSERVATIONS:
S.No. Voltage (V) Current I (mA) Power = V X I
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RESULT: Characteristics of solar cell are studied and fill factor is calculated.
Viva Question:
1. What factors may contribute to the lack of efficiency of the solar cell?
2. What does the energy output of a solar cell depend up on?
3. Why is it important to find out the highest power output for a solar cell?
4. Depending up on your observations , what are the best conditions for gaining
the maximum power from a solar cell?
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9. ENERGY BAND GAP
Aim:
To determine the width of the forbidden energy gap in a semiconductor
material using reverse biased p-n junction diode method.
Apparatus:
Power supply, heating arrangement, thermometer, micro ammeter, germanium
diode.
Principle:
The width of the forbidden
Energy gap [ ] = 2.3026 x 103 x K x slope Joules
K=Boltzmann constant = 1.38 X
m=slope of the line from the graph drawn between log Ioand
103/T
=
eV
Graph:
Circuit:
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Procedure:
The circuit is connected as shown in the fig. The semiconductor diode is
impressed in an oil bath which is heated by heating element. The thermometer is kept
in the oil bath to measure the temperature. The power supply is switched ON and the
voltage is adjusted to say 10 Volts. The current through the diode and the room
temperature are noted. The heating element is switched ON and the oil bath is heated
upto 90oC.The heating element is switched off when the temperature of oil bath
reached to 90oC.The power supply is again switched on and the voltage is kept at
10V. The oil bath is allowed to cool slowly. As the temperature falls the current
through the diode decrease. As the temperature fall through step of 5oC the
corresponding temperature are noted in the table.A graph is plotted between
on
x-axis and the logIo on y-axis. A straight line is obtained as shown in the graph. The
slope of the straight line is determined and calculated the band gap Eg.
Observation: Applied Voltage V=
Precautions:
1. The current flow should not be too high, if the current is high then the internal
heating of the device will occur. This will cause actual temperature of the
junction to be higher than the measured value. This will produce non-linearity
in the curve.
2. There may be contact potentials, thermo emfs and meter dc offsets which must
be add and subtract from the readings.
S.No Temperature to C Temp(T)=(273+t) kelvin
Current(I)µA
=R Log R
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3. Poor contacts result in huge variations in the results and must be carefully
soldered.
4. It is better to repeat a few measurements at end of each run to check the source
of error.
RESULT:
Energy Gap of p-n junction diode = __________ eV
Viva Questions:
1. What is a semiconductor?
2. Why Germanium specimen is preferred over silicon specimen? Why?
3. What are the units of energy gap?
4. Differentiate between conductors, semiconductors and insulators.
5. What is meant by doping?
6. What happens if the temperature of oil bath exceeds 90o C?
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10. STEWART & GEE’S EXPERIMENT
(Magnetic field along the axis of a coil)
AIM:
To determine the field of induction at several points on the axis of a circular
coil carrying current using Stewart and Gee‟s method.
Apparatus:
Stewart gee‟s experiment, battery eliminator, ammeter, connecting wires,
commutator, rheostat, plug key, compass.
Principle: Magnetic induction in the central axis of the coil
B =
Where B is the magnetic induction on the axial line of the coil
= 4π x10-7 N/𝐴
n - Number of turns in the coil
i - the current through the coil
a - the radius of the coil (in mts)=
- Permeability of free space
According to tangent layer:
Magnetic induction B = Be tan
Be – Horizontal magnetic component.=0.39X Tesla
When the coil is placed in the magnetic field it will be perpendicular to the
magnetic meridian, i.e., perpendicular to the direction of the horizontal component of
the earth‟s field. When the deflection magnetometer is placed at any point on the axis
of the coil such that the centre of the magnetic needle lies exactly on the axis of the
coil, then the needle is acted upon by two fields B and Be which are right angles to
one another. Therefore, the needle deflects obeying the tangent law.
Figure:
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Procedure:
With the help of the deflection magnetometer and a chalk, a long line of about
one meter is drawn on the working table to represent the magnetic meridian. Draw
the perpendicular lines to this line and place the coil of Stewart and gee‟s apparatus
in the magnetic meridian line. This coil is connected by connecting wires as shown
the fig. The deflection magnetometer is set at the centre of the coil and rotated to
make the aluminum pointer reading (0, 0) in the magnetometer.
The deflection reading before and after reversal of the current with the help of
commutator in the circuit are noted at distance d=0. The magnetometer is moved
towards east along the axis of the coil in steps of 5cm at a time. At each position the
deflections before and after reversal of current are noted. The deflections are noted
upto 20cm on the x-axis east side. The mean deflection is noted as .
The experiment is repeated by shifting the magnetometer towards west side
from the centre of the coil in steps of 5cm each time and deflections are noted before
and after reversal of current. The mean deflection is denoted as . A graph is drawn
between the distance on x-axis and the θ on y-axis. The slope of the curve is shown
in the fig. The points A and B marked on the curve lie at distance equal to half the
radius of the coil on either side of the coil.
Observation:
Current through the coil = i = ……………amps.
Number of turns in the coil = n = ………..
Radius of the coil (in meters) = a = …………. m
= 4π x 10-7
X
(cm)
DEFLECTIONS N
RIGHT ARM
DEFLECTIONS IN
LEFT ARM
MEAN,
B(x) = BE
Tan
B(x) =
{{
}
} 1 2 3 4 W 5 6 7 8 E
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Calculations:
Precautions:
The ammeter, voltmeter should keep away from the deflection magnetometer
because these meters will affect the deflection in magnetometer.
The current passing through rheostat will produce magnetic field and magnetic
field produced by the permanent magnet inside the ammeter will affect the
deflection reading.
Result:
It will be found that for each distance(X) the values in the last two columns are
found to be equal in table.
Viva Questions:
1. What is the direction of magnetic field at the centre of the coil?
2. Define magnetic meridian?
3. Where magnetic field is maximum in Stewart-Gee‟s method?
4. Define magnetic field induction (B), give its units?
5. State some of the applications of magnetic field produced by a circular coil?
6. Among Helmholtz galvanometer and moving coil galvanometer, which one is
more sensitive, explain?
7. in the preset experiment why galvanometer should be kept away from
ammeter and rheostat?
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11. Dispersive Power of the Prism
Aim:
To determine the dispersive power of the material of the given prism.
Apparatus:
Spectrometer, Mercury vapor lamp, glass prism, reading lens.
Principle:
The dispersive power of a prism = ω =
- Refractive index of Red light.
- Refractive index of blue light.
μ =
Refractive index μ =
A - Angle of the prism.
D - Minimum deviation.
Adjustments of the Spectrometer: The essential parts of the spectrometer are a)the
telescope b)collimator c)Prism table
Telescope adjustment:
The telescope is turned towards a distant object and its length is adjusted until
the distant object is clearly seen in the plane of the cross-wires.
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The telescope is turned towards a white wall and the eyepiece is adjusted so
that the cross-wire is very clearly seen. This ensures that whenever an image is
clearly seen on the cross-wire, it may be taken that the rays entering the telescope
constitute a parallel bundle.
Collimeter adjustment:
The slit of the collimeter is illuminated with light. The telescope is turned to
view the image of the slit and the collimeter screw is adjusted such that a clear image
of the slit is obtained without parallel in the plane of the cross-wire. This slit is
narrowed by adjustment of the slit screw and coincides with vertical cross-wire of the
telescope.
Prism table and base of the instrument:
The instrument base is leveled by adjusting the leveling screws with the help
of spirit level. And prism table also leveled by adjusting the leveling screws with the
help of the spirit level.
Scale Adjustment:
The scale adjustment zero of the Vernier scale should coincide with zero of the
main scale by Vernier adjustment when the cross-wire is coincided with slit image.
Procedure:
The prism is placed on the prism table with the ground surface of the prism to
the left or right side of the collimeter. The ray of light passing through the Collimeter
strikes the polished surface BC of the prism from the face AC. The deviated ray is
seen as spectrum through the telescope in position T2.
Looking at the spectrum the prism table is now slowly moved on to one side,
so that the spectrum moves towards the undeviated path of the beam. At one position
the spectrum starts turning back even though the prism table is moved in the same
direction. This position is called as minimum deviation position. At this position stop
the prism and cross-wire is made to coincide with red color and note the reading with
the help of the Vernier scale, recorded in the observation table. This procedure is
repeated with blue color and refractive index of these colors is calculated. This
dispersive power of the prism is calculated using given above formula.
Observations:
Least count of the Vernier of the spectrometer =
Angle of the prism (A) –
Direct ray reading
Vernier 1 –
Vernier 2 –
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S.No
Color of
the line
Reading corresponding to
minimum deviation
position
Angle of minimum
deviation=(Direct reading) -
(Reading of the minimum deviation
position)
Vernier 1 Vernier 2 Vernier 1 Vernier 2
1
Blue
2
Red
Precautions:
1. Take the readings without any parallax errors
2. The focus should be at the edge of green and blue rays
3. Don‟t touch polished surface of the prism with hands to avoid finger prints.
4. Use reading lens with light while taking the readings in Vernier scale.
5. The mercury light should be placed inside a wooden box.
Result:
Dispersive power of the prism ___________
Viva Questions:
1. What happen when rays of light of different colors travel in a glass prism
2. What is minimum deviation
3. What are the advantages in putting the prism in the minimum deviation
position
4. What are the spectrometer adjustment
5. Explain the Collimeter adjustment
6. What is telescope adjustment
7. What are the light properties
8. What is the visible wave length range
9. How to place the prism on the table
10. What is A0 unit?
Applications:
1. The dispersion of light in optical fibers.
2. The brilliance of diamond is due to its large dispersion.
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12. NEWTON’S RINGS
Aim:
To determine the Radius of curvature of the Plano convex lens (R) by forming
Newton‟s rings.
Apparatus:
Travelling microscope, sodium vapour lamp, Plano convex lens, a thick glass
plate, a magnifying glass.
Principle:
λ =
𝐴 R =
λ - Wave length of sodium light source.
R - Radius of curvature of the of Plano convex lens.
Dm- Diameter of the mth
ring.
Dn - Diameter of the nth
ring.
Graph:
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Experimental Arrangement:
Procedure:
The fig. shows the optical arrangement for obtaining in the Newton‟s rings.
The Plano convex lens and glass plate are held in position in a circular metallic
holder. It is placed on the travelling microscope. A plane glass plate is held above the
lens-glass plate combinations, inclined at the angle use with the vertical. The
condensing lens renders the light from the sodium vapour lamp to a beam of parallel
rays. This beam incident on the inclined glass plate is partially reflected from it and
is incident on the surface of Plano convex lens. The reflected beam from Plano
convex is partially reflected from it and reaches the microscope. The interface will
take place between the reflected beam from convex surface of the Plano convex lens
and the beam reflected from top of the plan glass plate.
The system is kept under the microscope and the microscope is focused to get
clear dark and bright rings in the field of view. First the microscope is adjusted so
that the centre of the cross wire coincides with central dark spot of the fringes
system. The microscope is then moved slowly towards left up to 20thrings and
reading is noted by micrometer. Next it moved in reversed direction up to 20th
ring
and the reading is noted. Similarly the reading noted for 18th
, 16th, 14th
.. rings left
side. After that the microscope is moved right side up to 10th
rings and noted the
reading. This procedure is repeated for rings on right side.
The difference in the readings of the tangential position of left and right of
cross wire for particular dark rings gives its diameter.
A graph is plotted for D2 diameter square (D
2) versus the number of the dark
ring (n).
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A straight line graph is obtained and slope of the graph is
Slope=
The wavelength of the sodium vapour lamp is calculated using the formula
λ =
𝐴
Observations:
Least count of the microscope (L.C):
mm.
Radius of curvature of the lens in contact with glass-plate-R=________cm.
Wave length of the Sodium Vapour light 𝜆 =
Precautions:
Notice that as you go away from the central dark spot the fringe width decreases. In
order to minimize the errors in measurement of the diameter of the rings the
following precautions should be taken:
i) The microscope should be parallel to the edge of the glass plate.
ii) If you place the cross wire tangential to the outer side of a perpendicular
ring on one side of the central spot then the cross wire should be placed
tangential to the inner side of the same ring on the other side of the central
spot.
iii) The traveling microscope should move only in one direction
S.No of
rings
(n)
Microscope
Reading(mm) Diameter of n
th
ring (D)
(L1 R1)
(mm)
Square of Diameter of
the ring (D²) Left side
L1
Right side
R1
20
18
16
14
12
10
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RESULT:
Wavelengths of the sodium vapour lamp _____________𝐴 (or)
Radius of curvature of the given plano convex lens R =
Viva Questions:
1. What is the aim of the experiment?
2. How are the Newton‟s rings formed?
3. Where are the rings formed?
4. Why are the rings circular and concentric?
5. Why is the central spot dark?
6. Why should lens of larger R be used in the experiment?
7. How will the rings change if we introduce a little water between the lens and
the plate?
8. What will happen if white light is used in place of sodium light?
9. What are the engineering applications of Newton‟s rings?
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13. DIFFRACTION GRATING
AIM: To determine the wave length of a given light using diffraction grating with
normal incidence method.
Apparatus:
Plane diffraction grating, spectrometer, sodium vapour lamp, reading lens.
Principle:
λ=
=
λ - Wavelength of light.
d – Grating spacing d =
N is no. of lines per cm.
n – Order of spectrum.
– Angle of deviation corresponding to nth order.
Figure:
PROCEDURE: In normal incident method the light ray is perpendicular incidental in the
grating plane. All adjustment in the spectrometer i.e., telescope adjustment,
Collimeter adjustment, scale adjustment & Prism base & instrument base adjustment
are adjusted and the spectrometer is ready.
The telescope s brought in time with the Collimeter to have image of the slit
on the vertical cross wire and locker in that position. The Vernier scale of the
spectrometer is unlocked and the table is rotated till the reading on one Vernier is
exactly 360o as show in the fig.
Now the telescope arm is unlocked and rotated through 90o in anti-clock wise
direction and it is locked in that position as shown in the fig2.
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The grating is placed on the prism table with its ruled surface towards the
telescope. The grating stand should at the centre of the prism table. Then the prism
table is rotated slowly, so that a reflected image is seen in the field view of the
telescope and coincided with vertical cross wire the prism table is locked in that
position. The angle of incidence of light on grating surface is 45o as shown in
fig3.The Vernier scale is rotated along with prism table through an angle 45o so that
the grating plane becomes normal to the direction of the light as shown in fig4.
Now the telescope is unlocked and rotated to bring it in line with the
Collimeter to receive the image of the slit on the cross-wires. The telescope is slowly
rotated to the right till the image of the slit corresponding to the first order is
coinciding with cross wire and the reading is noted. The difference between the two
positions gives the angle of deviation belonging to the first order. The telescope is
rotated further right side to get the image along to second order and the angle of
deviation is calculated and the readings are noted down in the table. The wavelength
is calculated using the formula.
OBSERVATIONS:
Number of lines per cm N =
Order of
the
spectrum
Line
Readings when the
telescope is in right
side
Direct reading
Difference
sin
𝜆
Vernier
1
Vernier
2
Vernier
1
Vernier
2
First order
Spectrum
D1
D2
D2
Second
order
Spectrum
D1
D2
D2
Precautions:
1. The experiment should be performed in a dark room.
2. Micrometer screw should be used for fine adjustment of the telescope. For
fine adjustment the telescope should be first licked by means of the head
screw.
3. The directions of rotation of the micrometer screw should be maintained
otherwise the play in the micrometer spindle might lead to errors.
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4. The spectral lams (mercury source) attain their full illuminating power after
being warmed up for about 5 minutes; observation should be taken after 5
minutes.
5. One of the essential precautions for the success of this experiment is to set
the grating normal to the incident rays (see below). Small variation on the
angle of incident causes correspondingly large error in the angle of diffraction.
If the exact normally is not observed, one find that the angle of diffraction
measured on the left and on the right are not exactly equal. Read both the
verniers to eliminate any errors due to non coincidence of the center of the
circular sale with the axis of rotation of the telescope or table.
RESULT:
Wavelength of the = ___________.
Wavelength of the =___________.
Viva Questions:
1. What is the aim of the experiment?
2. What is a diffraction grating?
3. What is meant by diffraction of light?
4. Where is the zero order fringes formed?
5. What is meant by diffraction of light?
6. What are the different types of grating?
7. Explain the normal incident method?
8. N representing _____________ per cm