Download physics _lab manual_2014_15_new syllabus

Laboratory Manual/Physics (EC) Department/IT/NU
Fundamental Units and Dimensions
Aim: To analyze fundamental units and dimensional formulas.
Introduction:





Physics is a science of exact measurement. In mechanics, the quantities mass,
length and time are chosen as fundamental quantities because these quantities
cannot be expressed in terms of any other more fundamental quantity.
A fundamental quantity is a quantity which cannot be expressed in terms of any
other physical quantity. The units in which these quantities are measured are
called fundamental units.
As there are mainly two types of physical quantities: Fundamental and Derived
there are two types of units.
Fundamental Units: These types of units can be defined without any help of
other units.
Derived units: These units are defined with the help of fundamental units and
therefore are called derived units.
Fundamental Units: (IN SI System)
Sr.
no.
1.
2.
3.
4.
5.
6.
7.
Physical Quantity
Unit
Symbol
Length
Mass
Time
Temperature
Quantity of Matter
Electric Current
Luminous Intensity
Meter
Kilogram
Second
Kelvin
Mole
Ampere
Candela
M
Kg
S
K
Mol
A
Cd
1
Laboratory Manual/Physics (EC) Department/IT/NU
Examples of Derived Units and Their Dimensional formulas:
Sr.
No.
1
2
3
4
Physical Quantity
6
7
8
Length
Area
Volume
Density
Relative Density or
Specific Gravity
Velocity
Acceleration
Force
9
Weight
10
11
12
13
14
20
Tension
Thrust
Pressure
Momentum
Impulse of Force
Moment of force or
Torque
Work
Kinetic Energy
Potential Energy
Angle or angular
displacement
Angular Velocity
21
Angular Acceleration
22
23
26
Angular Momentum
Angular Impulse
Universal Gravitational
Constant
Intensity of Electric
field
Electric Potential
27
Dielectric constant
5
15
16
17
18
19
24
25
28
29
30
Electric Dipole
Moment
Electrical Resistance
Potential energy of the
Capacitor
Formula
-Length x Length
Length x Length x Length
Mass / Volume
Density of Substance/ Density
of water
Distance / Time
Velocity / Time
Mass x Acceleration
Mass x Acceleration due to
gravity
Force
Normal Force
Force / Area
Mass x Velocity
Force x Time
Dimensional
formula
[M0L1T0]
[M0L2T0]
[M0L3T0]
[M1L-3T0]
Dimensionless
Quantity
[M0L1T-1]
[M0L1T-2]
[M1L1T-2]
[M1L1T-2]
[M1L1T-2]
[M1L1T-2]
[M1L-1T-2]
[M1L1T-1]
[M1L1T-1]
Force x Distance form the point
[M1L2T-2]
Force x displacement
(½) Mass x Velocity2
Mxgxh
[M1L2T-2]
[M1L2T-2]
[M1L2T-2]
Arc / Radius = L / L
No Dimension
Angular Displacement / Time
Change in Angular Velocity /
Time
Mass x Velocity x Distance
Torque x Time
[M0L0T-1]
F x R2 / M1M2
[M-1L3T-2]
Force / Charge
[A-1M1L1T-3]
Work / Charge
[A-1M1L2T-3]

0
[M0L0T-2]
[M1L2T-1]
[M1L2T-1]
No Dimension
Charge x Distance
[A1M0L1T1]
Voltage / current
[A-2M1L2T-3]
(1/2) C x V2
[A0M1L2T-2]
2
Laboratory Manual/Physics (EC) Department/IT/NU
Quiz
Sr.
No.
Physical Quantity
1.
Gravitational Potential
2.
Moment of Inertia
3.
Current Density
4.
Capacitance
5.
Specific resistance
6.
Electrical Conductivity
7.
Intensity of Magnetic
field
8.
Magnetic Flux
9.
Surface Tension
10.
Force Constant
11.
Coefficient of
Viscosity
12.
Stress
13.
Self Induction
14.
Mutual Induction
15.
Permeability of
Vacuum
16.

17.
Planck’s Constant
18.
Charge
19.
Potential Gradient
0
Formula
0
Date:
Sign of Faculty:
3
Dimensional
formula
Laboratory Manual/Physics (EC) Department/IT/NU
Solar Cell Characteristics
Aim: Estimation of the solar energy in terms of solar power and V-I characteristics,
Power load characteristics of the solar cell.
Apparatus:
1. Solar cell mounted
2. Table lamp 100 W
3. Experimental set up board
Theory:
A solar cell is basically a P-N junction which converts solar energy into electrical
energy. Such conversion of optical energy into the electrical energy is known as
photovoltaic effect and therefore solar cell is also called as photovoltaic cell. Solar cells
are composed of various semi conducting materials. Over 95% of all the solar cells
produced worldwide are composed of the semiconductor material Silicon (Si). To
produce a solar cell, the semiconductor is "doped" with which one can obtain a surplus
of either positive charge carriers (p-conducting semiconductor layer) or negative charge
carriers (n-conducting semiconductor layer) from the semiconductor material. When the
solar cell is illuminated, the photons incident on the cell generate electron hole pairs. At
the junction, the barrier field separates the positive and negative charge carriers. Under
the effect of electric field, the electrons (minority carriers) from p side are swept in to n
region. A similar process occurs to holes in n region. This leads to an increase in the
number of holes in p- region and of electrons in n- region. Hence, such accumulation of
charges on the both sides of the junction produces an emf which is called a photo emf,
which is also known as open circuit voltage and is proportional to the illumination
(mW/cm2 or lumen/cm2) and the size of the illuminated area. When an external circuit is
connected across the solar cell terminals, the minority carriers return to their original
sides through the external circuit, causing the current to flow through circuit. Thus, the
solar cell is behaves like a battery with n- side as the negative terminal and p-side as a
positive terminal. The photo emf can be measured with a voltmeter.
The output (product of current and voltage) of a solar cell is temperature
dependent. Higher cell temperatures lead to lower output, and hence to lower efficiency.
The level of efficiency indicates how much of the radiated quantity of light is converted
into useable electrical energy. About 24% efficiency is achieved at the lab level with the
4
Laboratory Manual/Physics (EC) Department/IT/NU
help of Monocrystalline Silicon. Following steps may be helpful for higher efficiency of
the solar cell panel:

Construction of the cell surface in a pyramid structure, so that incoming light hits
the surface several times. New material: for example, gallium arsenide (GaAs),
cadmium telluride (CdTe) or copper indium selenide (CuInSe²).

in order to be able to use a wide spectrum of radiation, different semiconductor
materials, which are suited for different spectral ranges, will be arranged one on
top of the other.

A higher light intensity will be focused on the solar cells by the use of mirror and
lens systems. This system tracks the sun, always using direct radiation.
1. Illumination Characteristics:
Procedure:
1.1 Make the circuit as shown in Fig. 1.
1.2 Allow the light from a 100 W bulb on the solar panel. Keep the intensity control
at its minimum and make the lamp on.
1.3 Keep the load at 0 Ohm and note down the short circuit current.
1.4 Vary the intensity of lamp in steps and note down the current at each setting. Note
down the readings in the given table 1.
1.5 Draw the graph between current versus intensity (in terms of lamp voltage) as
5
Laboratory Manual/Physics (EC) Department/IT/NU
shown in the Fig. 2.
Observations: Table -1. Illumination Characteristics
Sr. No.
Intensity (DC Volts)
RL=0 Ohm
Current (DC mA)
1
2
3
4
5
6
7
8
9
10
2. Current – Voltage Characteristics:
Procedure:
2.1 Keep the intensity of lamp at its minimum, say I1. Make the load resistance RL =0.
Note the open circuit voltage and short circuit current in the tabulation 2.
2.2 Now vary the load dial in steps of 100 Ohms up to 900 Ohms and note down the
current and voltage readings in the table 2.
2.3 Repeat the above step for high lamp intensity, say for I2 and furthermore
for I3 and note down the readings in table 2.
6
Laboratory Manual/Physics (EC) Department/IT/NU
2.4 Plot the graph for Current versus voltage for maximum intensity I3 and minimum
intensity I1 as shown in Fig. 3.
Observations: Table -2 Current – Voltage Characteristics
Sr.
RL
No.
Ohms
1
0
2
100
3
200
4
300
5
400
6
500
7
600
8
700
9
800
10
900
11
∞
Intensity I1=50
Intensity I2=100
Intensity I3=150
V
I
V
I
V
I
(Volts)
(mA)
(Volts)
(mA)
(Volts)
(mA)
7
Laboratory Manual/Physics (EC) Department/IT/NU
Graph:
Result:
At following different Intensities
Sr. No.
Quantity
I1
I2
______ Volts
1
Open Circuit
Voltage (RL=∞)
______ Volts
2
Short Circuit
Current (RL=0)
______ mA
______
I3
mA
______
______
Volts
mA
3. Power – Load characteristics:
Procedure:
3.1 Calculate the output power using the sets of readings of voltage and current of
table 2 for the intensities I1, I2 and I3 and enter into the table 3.
3.2 Plot the graph of power versus load as shown in the fig. 4 and determine the value
of optimum load that draws the maximum power from the panel.
8
Laboratory Manual/Physics (EC) Department/IT/NU
Observations: Table -3 Power – Load Characteristics
Sr. No.
RL Ohms
1
0
2
100
3
200
4
300
5
400
6
500
7
600
8
700
9
800
10
900
11
∞
Power for
Power for
Power for
Intensity I1
Intensity I2
Intensity I3
(mW)
(mW)
(mW)
Result:
At following different Intensities
Sr. No.
Quantity
I1
I2
I3
1
Max. Power
Pmax
------mW
------mW
------mW
2
RL at Pmax
------Ohms
-------Ohms
------Ohms
The Maximum Power Output is found to be ________ mW.
9
Laboratory Manual/Physics (EC) Department/IT/NU
Graph:
Quiz:
1. What is solar cell? Give its applications.
2. Give the construction of solar cell penal with proper schematic diagram.
3. On which parameters, the efficiency of the solar cell penal depends?
4. What are the different ways to improve the efficiency of the solar cell?
5. Write a note on the contribution of Paul M Dirac in Physics.
Date:
Sign of Faculty:
10
Laboratory Manual/Physics (EC) Department/IT/NU
e/m FOR AN ELECTRON BY THOMSON
METHOD
Aim: Evaluating the charge to mass ratio for electron by applying perpendicular
magnetic field on the electron beam in CRT
Apparatus: Magnetometer wit wooden bench, two bar magnets, cathode ray tube \
(CRT), Power supply.
Procedure:

The wooden frame & the wooden bench are coupled together as shown in figure
.A magnetometer is kept on the wooden bench such that 90 -90 diameter of its
circular scale is parallel to the length of the bench

The entire setup is oriented such that the pointer of the magnetometer coincides
with 0-0 markings. This setting ensures tat when CRT is placed instead of the
component of the earth’s magnetic field will be ineffective to influence the
electron beam. Once the position is adjusted. It is undisturbed till the experiment
is completed.

The wooden bench is removed and the CRT is introduced in its place as shown in
figure, the CRT is connected to the power supply. The power supply is switched
on adjusting the intensity and focus controls a spot of sufficient brightness is
obtained using X- and Y- shift controls it is brought to the center of screen.

Now apply a suitable deflecting voltage so that the lamination spot is deflected by
about 0.5to 1.0 cm. Note the deflecting voltage V and position of the spot.
Measure the distance through which the spot has moved and let it be D.

Place the bar magnets symmetrically on either side of the cathode ray tube along
the arms of the wooden stand on which the tube is fitted such that their opposite
poles face each other and their common axis is exactly at right angles o the axis of
the cathode ray tube adjust the polarity as well as the distance of the magnets so
that the luminous spot comes back tots initial position. When the adjustment is
perfect note the distance of the poles of the magnets on the side nearer to the
cathode ray tube let the distance be r1 and r2.

Remove the bar magnets switch off the electric field off the electric field applied
to the deflecting plates and again note the initial position of the luminous spot.
11
Laboratory Manual/Physics (EC) Department/IT/NU
Reverse the polarity of the potential difference applied to the luminous spot and
calculate D.
Again place the bar magnets on the arms of the wooden stand as in the previous
step and adjust their polarity as well as distance so that the spot comes back to its
initial position. When the adjustment is perfect again note the distance of the
poles of the magnets on the side nearer to the cathode ray tube let the distance be
r1’ and r2’ switch off power supply.

To find the value of the magnetic field, carefully remove the magnets and the
cathode ray tube from the wooden stand place the compass box such that its
center lies exactly on the point where the common axis of the bar magnets and the
axis of the cathode ray tube intersect. Rotate the compass box about its vertical
axis so that the pointer lies along the 0-0 lines.
Place the magnets exactly in the same positions as in steps 5 an distance r 1 and r2.
This produces a deflection in the magnetometer compass box and the two ends of
the pointer deflection let the readings be θ1and θ2
Now place the magnets exactly in the same position as in step 6 at distance r 1 and
r2 and note the deflection θ1’and θ2’ from the two ends of the pointer of the
compass box. The mean of these four deflection θ1, θ2, θ1’and θ2’ gives the mean
deflection θ if BH is the horizontal component of earth’s magnetic field then,
B  BH tan 
Where BH is the earth’s horizontal component of the field. It is different at the
different place.

Take two more sets of observations by changing the values of B and hence that of
electric field.
Observations:
1. Length of deflecting plates (l) = 0.045 meters
2. Separation between deflecting plates (d) = 0.0245 meters
3. Distance of the screen from the edges of the y-plate (L) = 0.125 meter
4. Horizontal component of earth’s magnetic field BH = 0.36×10-4 Tesla
12
Laboratory Manual/Physics (EC) Department/IT/NU
Observations Table:
Direct field
Sr.
No.
Applied
Voltage
Initial Final
1
Magnetic pole and
Distance
Position of Spot
V
V1 =
Deflection
D in meter
Reversed Field
Pole
r1
Pole
Magnetic pole and
Distance
Position of Spot
r2
Initial
Final
D1 =
Deflection D
in meter
Pole
r'1
Pole
D1 =
For determination of B
Sr.
Reading of two ends of pointer
Reading of two ends of pointer
when magnetic poles are at r1 & r2
when magnetic poles are at r1’ & r2’
No.
θ1
1
θ2
θ1 ’
θ2 ’
Mean θ
B  BH tan 
r’2
Laboratory Manual of Physics (PY101)
Calculation:
e
m

V1 D1
 ______________ C Kg-1
LdlB12
Quiz:
1. Write brief note on contribution in physics by Sir Thomas Alva Edison.
2. Draw diagram of CRT and discuss about its main parts.
3. Why CRT is to be highly evacuated?
4. Why do we need to orient entire set up in magnetic meridian before performing
experiment?
5. In this experiment, the accuracy in the value of e/m largely depends upon which
factor? Why?
6. Can we use single bar magnet? Justify your answer.
7. The magnetic needle in the magnetometer aligns in which direction? Write answer in
both polar and geographical terms.
Date:
Sign of Faculty
14
Laboratory Manual of Physics (PY101)
emf GENERATION BY DYNAMIC MAGNETIC
FIELD
Aim: To measure the electro motive force by dynamic magnetic field and verification of
Faraday’s law
Theory:
The basic principle of generation of alternating e.m.f is electromagnetic induction
was discovered by Michael Faraday. This phenomenon is the production of an induced e.m.f
in a circuit caused by change of the magnetic flux linking the circuit. Faraday’s laws of
induction tells us that the induced e.m.f is given by,
   t
It represents the rate of change of flux linking the circuit. In MKS unit ε will be in volts, the
flux will be in Weber and t in second.
APPARTUS:
In this experiment, we are using OMEGA TYPE ES_232 kit. It consists of a
permanent magnet mounted on an arc of a semi-circle of radius 40 cm. The arc is a part of
rigid frame of aluminum and I suspended at the center of the arc so that the whole frame can
oscillate freely in its plane. (See figure 1).
15
Laboratory Manual of Physics (PY101)
Weights have been provided on the diagonal arm so that by alternating their positions the
time period of the oscillations can be varied from about 1.5 to 3 seconds. Two coils of about
10,000 turns of copper wire loop the arc so that the magnet can pass freely through the coil.
The two coils are independent and can be connected either in series or in parallel. The
amplitude of the swing can be read from the graduated circle by pointer. On the panel of the
measurement board one voltmeter with four ranges 0-2.5 V, 5 V, 10 V and 20 V and one
ammeter with two ranges 1 mA, 2.5 mA are provided. Board also has four different valued
condensers, five resistances and two diodes and one SPST switch for performing
experiments.
Magnet N-S passes through a coil C (by using coil 1 or 2) with varying velocities
(See figure 2). A Aluminum frame can be swing about a pivot O, it’s period adjustable
sliding the loads A, A. if D is released from an angle  0 from the equilibrium, the velocity
Vmax with which the magnet passes the coil is given by,
4
sin


V

P

02

max
T  
P is the distance between the arc center and the weight. The magnetic flux through the coil
changes as the magnet NS passes through it.
Procedure:
1. Connect the circuit as shown in figure 3. Keep the switch S in off position. Here R1 is
the internal resistance of the coil and the forward resistances of the coil and the forward
resistance of the diode. Capacitor is of 100 F. At each swing the diode permits the
capacitor to gain a charge once. The charging time RC = 50ms, the capacitor reaches the
value in a few swings.
2. When the Milli-ammeter shows no more kicks, it means the capacitor C has reached the
potential E0. Measure this potential by changing switch on position and take reading on
voltmeter.
3. Vary Vmax by choosing different  0 values and measure E0 each time.
4. Plot a graph of E0 versus Vmax and observe it is linear.
5. The ideal graph given below shows the results of an experiment.
16
Laboratory Manual of Physics (PY101)
Observation Table:
Sr.
No.
Angle  0
Induced EMF Vmax cm/Sec
Quiz:
1. Define electromagnetic induction.
2. Write all three statement of Faraday’s law for electromagnetic induction.
3. Write integral and differential form of Faraday’s law.
4. How can you say that AC emf is induced in the coil?
5. What is the use of a capacitor and diode in this experiment?
6. What is the practical use of Faraday’s law? List out five of them.
7. Write a brief note on contribution in physics by Dr. Vikram Sarabhai.
Date:
Sign of Faculty
17
Laboratory Manual of Physics (PY101)
STUDY OF TRANSFORMER
Aim: Energy Efficiency measurement of a power transformer.
Apparatus: OMEGA TYPE ETB-110.
Features of the Board:
The board consists of following built-in parts:
1. Main transformer with primary 230 V at 50 HZ and secondary out put at 0-10 V A.C.
at 1 ampere.
2. AC/DC voltmeter, to measure the mains input to the transformer of 0-250 V.
3. AC/DC milli-ammeter, to measure the primary circuit current of 0-100 mA.
4. AC/DC voltmeter, to measure the secondary voltage of 0-15 V.
5. AC/DC Ammeter, to measure the secondary circuit current of 0-1Amp.
6. High Wattage rating Potentiometer for transformer’s primary voltage variations.
7. High Wattage rating Potentiometer to be used as a load for the secondary circuit.
Theory:

When an alternating current passes through a conductor, the magnetic field is
produced across it. The direction of the field is shown in figure 1.

When a varying DC current passes through an inductor, the magnetic field
lines are produced around it. It is shown in fig. 2.
18
Laboratory Manual of Physics (PY101)

When an alternating current passes through an inductor, the magnetic flux is
produced around the inductor and the direction of the magnetic field changes
after each half cycle of the applied signal. This is shown in fig. 3.

When an alternating current is flowing in one coil it induces voltage in the
neighboring coil. The changing magnetic field lines in one coil cuts the turns
of the other coil and induce a changing voltage in each of the turn in the
neighboring coil. Transformer works on this principle. The transformer serves
many functions. It enables the transform of electrical energy from one
electrical circuit to another by using changing magnetic field lines as the
linked between the two. In this way it behaves as coupling device. Also, it
provides a mean by which an alternating voltage of given amount can be
changed to higher or lower amount. Transformer is a electro-magnetic circuit
consisting of two windings namely primary and secondary. They are the
bobbins on which winding is done and then are laminated. A practical
transformer wound on the tack of E and I shape strips of iron core are shown
in fig. 4.
The alternating emf, which is to be transformed, is applied to the primary coil. The
alternating current in the primary gives rise to flux change. This change of flux induces e.m.f
in the secondary coil by mutual coupling and also produces self-induced e.m.f in the primary.
Evidently, e.m.f in the secondary depends on the following factors.
1. The number of turns on the primary and secondary coil.
2. The e.m.f applied across the primary.
3. The co-efficient of mutual induction.
4. The co-efficient of self-induction of primary and secondary coils.
19
Laboratory Manual of Physics (PY101)
5. The Ohmic resistance of the coils & the frequency of the alternating current.
Voltage Transformer:
If Ep were the applied e.m.f across the primary of turns Np, the e.m.f induced in the
secondary of turns Ns is given by,
EN
s
s
EN
p
p
.
.
.
.
.
.
.
.
.
. (
1
)
Here equation 1 gives the transformer ratio. If Es › Ep. The transformer is called step up
transformer. If Ep › Es then the transformer is called as step down transformer. These are
shown in figure 5.
Current Transformer:
We know that the impendence in an AC circuit of resistance Rs, self-inductance Ls and AC
of angular frequency w is given by,
2
22
ZR

(s


L
)
s
.
.
.
.
.
.
.
.(
2
)
Let Rs and Ls stand for the secondary of the transformer. Now if the secondary is made of
thick copper wires or strips Rs ‹‹ w Ls. A necessary condition for current transformer ratio,
N
C
s
p
.
.
.
.
.
.
.
.
.
.
C
N
p
s
(
3
)
Meaning the current transformer is inversely related to the number of turns.
20
Laboratory Manual of Physics (PY101)
Effects of secondary:
It may be shown that the resistance of the primary increases because of the induced currents
in the secondary. Thus the effective resistance of primary in the presence of the secondary
becomes,

M
R
R

R
R


L
2
2
s
P
2
22
S
S
(
4
)
Similarly the effective inductance is given by,
2
2

M
R
s
L

L
(
5
)
P
2
22
R


L
N
N
Where Rp and Rs are the resistances of the primary and secondary coils. M and Ls are the
co-efficient of mutual induction and the self-induction of secondary. The above-mentioned
discussion is applied to AC circuits.
Efficiency of transformer:
The efficiency of a transformer is defined as the ratio of output energy from the secondary to
the input in the primary,
C
o
u
t
p
u
t
e
n
e
r
g
yE


 
1
0
0
I
n
p
u
t
E
n
e
r
g
yE
C
s s
(6)
PP
Copper Loss:
When the current passes through the primary coil, a part of the electrical energy is converted
into heat, this loss is due to the resistance of the copper coil. Therefore it is called copper
loss. The secondary reflects an additional resistance in the primary; therefore the current in
the secondary must be kept constant for copper loss determination.
Iron Loss:
Iron losses occur in transformer because of (i) Hysteresis and (ii) eddy currents. To minimize
these losses a laminated core of suitable iron is used.
21
Laboratory Manual of Physics (PY101)
Procedure:
Connect the circuit as shown in fig.-6. For this, connect the respective terminal marked link
in fig. 7.
1.
2.
3.
4.
5.
6.
7.
Switch on the supply.
Set the position of pots VR1 and VR2 anywhere.
Measure the primary and secondary voltages and currents.
Calculate the transformer ratio by equation 1.
Calculate the efficiency using relation 6.
Calculate the copper loss using this equation: Copper loss = Ep x Cp watts
Change the position of VR1 and VR2 and repeat the step (4) above and calculate
transformation ratio, Efficiency and copper loss.
Observation Table:
Sr.
No.
1
2
3
4
5
6
7
8
Primary
Voltage
Ep
200 V
190 V
180 V
170 V
160 V
150 V
140 V
130 V
Primary
Current
Cp
Secondary
Voltage
Es
Secondary
Current
Cs
Ep / Es
=Np / Ns
Quiz:
1.
2.
3.
4.
5.
6.
7.
8.
What is the principal of working of transformer?
Can we use DC current in this experiment?
Why do we use iron core? Which type of material it is?
What is copper loss? How can we reduce the copper loss in the circuit?
What is hysteresis loss? Define retaintivity and coercivity.
Write a short note on uses of eddy current.
What are the practical uses of transformer? List at least five of them.
Write brief note on Dr. APJ Abdul Kalam.
Date:
Sign of Faculty:
22
Efficiency
Laboratory Manual of Physics (PY101)
RESITIVITY MEASUREMENT BY FOUR POINT
PROBE METHOD
Aim: To measure the resistivity of semiconductor by four point probe method at
different temperature.
Apparatus: Omega type ES-246 (The instrument is absolutely self contained and
requires no other apparatus.)
Theory:
The properties of the bulk materials used for the fabrication of transistors and other
semiconductors devices are essential in determining the characteristics of the complete
devices. Resistivity and lifetime measurements are generally made of germanium crystal to
determine their suitability. The resistivity, in particular must be measured accurately since
its value is critical in many devices. In solids, atoms are usually arranged in a regular way to
achieve dense packing and thereby form a crystal. The arrangement has very desirable
characteristics; i.e. the transport of holes and free electrons is very smooth in these electrons.
As a result of interaction between the tremendous numbers of atoms in crystal, the energy
level found in isolated atoms will be spilt and form bands of allowed energies which contain
almost continuum levels. The unoccupied energy levels also split up and form another band
called conduction band. The interaction between the unused shells is very large and they
spread widely. Therefore, while there is a band gap, Eg between the valance and conduction
band, splitting of higher orbit is so wide that they usually overlap.
According theory, an insulator must have a large band gap, so that at room
temperature the conduction band is completely empty and valance band is practically filled
and semiconductors must have narrow band gaps so that appreciable number of carriers is
present in the valance and conduction band at room temperature.
Four Point Probe Method:
It permits the measurements of resistivity in samples having a wide variety of shapes,
including the resistivity of small volumes within bigger pieces of semiconductor. In this
manner the resistivity of both sides of p-n junction can be determined with good accuracy
before the material is cut into bars for making devices.
Procedure:
 Put the sample on the base plate of the four probe arrangement. Unscrew the pipe holding the
four probes and let the four probes rest in the middle of the sample.
23
Laboratory Manual of Physics (PY101)
 Connect the outer pairs of probes (green leads to the constant current power supply) and the
inner pair (red labels) to the probe voltage terminals.
 Place the four probe arrangement in the oven and fix the thermometer in the oven through
the hole provided.
 Switch on the AC mains of four probe set up and put the digital panel meter in the current
measuring mode through the selector switch. In this position LED facing mA would glow.
Adjust the current to a desired value (say 5 mA).
 Now put the digital panel meter in voltage measuring mode. In this position LED facing mV
of V would glow depending on position of switch and the meter would read the voltage
between the probes.
 Connect the oven power supply. Rate of heating may be selected wit the help of S switchLow or High as desired. Switch on the power to the oven. Te glowing LED indicated power
to the oven is ON.
Figure 6.1: Measurement of resistivity using Four Point Probe Method
Observations:
1.
Current I = 5
mA (Constant)
2. Width of the chip (W) =
0.05
3. Distance between two probes (S) =
4. G7 (W / S ) =
cm
0.2
cm
2S log2
W e = 5.546
24
Laboratory Manual of Physics (PY101)
Formulas:
1. To calculate ρ use the following equation:

0
 
W
G
7
S
0  2S
V
I
Where,

2
k
log
2
k
(
slope
)
E
 e 
eV
g
=__________ eV
1
e
T
where, k= Boltzmann constant= 1.38×10-23 J/˚K
loge ρ
2. The Energy Band Gap=
1/T (K-1)
Observation Table:
Temperature
Sr.
No.
(ºC)
Voltage
ρ0
ρ
(Volt)
(Ω cm)
(Ω cm)
(ºK)
1
2
3
4
5
6
7
8
25
logeρ
1/T
(K-1)
Laboratory Manual of Physics (PY101)
Quiz:
1. Write a working principle of four point probe method.
2. How will u distinguish between insulator, conductor and semiconductor?
3. Draw the band structure of insulator, conductor and semiconductor.
4. What are the requirements to measure resistivity accurately using this method?
5. Can we perform the experiment using only two probes only? Why?
6. What is physical significance of band Gap?
7. Write a microscopic form of Ohms’ law.
8. Which type of material has higher conductivity- P type or N-type? Justify your
answer.
9. What are the advantages of four probe method over the conventional method used to
measure the resistivity of semiconductor?
10. Write brief not on contribution in physics by Prof. C V Raman.
Date:
Sign of Faculty
26
Laboratory Manual of Physics (PY101)
Band Gap Determination in Semiconductor diode
Aim: Determination of forbidden energy band gap in a semiconductor using a junction
diode.
Apparatus: An experimental board consists of digital micro-ammeter, oven, semiconductor
diode, and thermometer.
Theory:
In a material, the energy difference between its non-conductive state (valance band) and its
conductive state (conduction band) is referred to as energy band gap or forbidden gap. In
other words, the band gap is the energy it takes to move electrons from the valence band to
the conduction band. The existence of energy band gap is successfully explained by Band
theory of solids using Linear Combination of Atomic Orbital (LCAO).
Procedure:
1. Insert the thermometer in the hole of an oven and switch on the power supply.
2. Insert the two leads to the diode in the socket i.e. insert red plug in +ve socket and
black plug in – ve socket as shown in the fig 1.
3. Now turn the oven on and allow the temperature to rise up to 75˚ C only.
4. As soon as the temperature reaches to 75˚ C, switch off the oven and let stabilize the
temperature around 70˚ C.
5. Now start to take the readings of temperature by taking current as reference i.e. for
each step of 10 µA of current reduction, note down the readings of temperature
from the thermometer in table 1.
6. Plot the graph of log Is versus 103/T as shown in the fig. 2 and determine the slope
of the line.
27
Laboratory Manual of Physics (PY101)
Fig. 1 The practical circuit diagram
28
Laboratory Manual of Physics (PY101)
Observation Table-1.
Sr. No.
Reverse
Saturation
Current iS
(µA)
Temperature
˚C
1/T (˚K-1)
˚K
Log is
3
(×10 )
1
2
3
4
5
6
7
8
9
10
Graph:
Determine the slope of the line and find the slope of the line to calculate the band gap as
slope
ofline

E

= --------- eV
5
.036
From any point C on the line draw a perpendicular projection on the x-axis and y-axis. Slope
of the graph is CD/CE.
Fig 2 Graph of log is versus 1/T
29
Laboratory Manual of Physics (PY101)
Quiz:
1. What is the criterion for a material for possessing semi conducting properties?
2. Give the fundamental Classification of a solid based on energy band gap.
3. What do you mean by energy band gap? What is the reason behind its existence?
4. Give the categories of semiconductor based on energy band gap. Define each.
5. What are the other methods to measure the energy band gap of semiconductor?
6. What are the advantages and disadvantages (if any) of energy band gap of a
semiconductor?
7. Write brief note on contribution in physics by Max Plank
Date:
Sign of Faculty:
30
Laboratory Manual of Physics (PY101)
MEASUREMENT OF THIN FILM AND
WAVELENGTH OF MONOCHROMATIC
LIGHT
Aim: To measure the wavelength of light from sodium vapor lamp and find the thickness
of thin film using Newton’s rings method.
Apparatus: Newton’s ring apparatus, wooden reflector, traveling microscope, sodium
Light source, lens.
Theory:
The formation of Newton’s rings is due to the interference of light waves reflected
from the upper and lower surface of the air film enclosed between the lens and the plan glass
plate. The thickness of the air film at the point of the contact is zero and increases as we
move from the point of contact towards the periphery of the lens. The thickness of the air
film will be uniform for all points lying on the circle with centre at the point of contact. Thus
using reflected light, the central point will be dark surrounded by bright circles separated by
dark rings.
If R is the radius of curvature of the lens and t is the thickness of the air film at A or
B, the necessary condition for bright fringes using reflected light is

n

1
2

tcos
2
2
Where, n = 0,1,2,……….. Since θ is very small cos θ=1 ( θ is angle of refraction).
2n1
2t
Here for air μ=1.
2
2n
2t
And for dark fringes,
2
Now, from the geometry of figure,
(EB) (AE) = (EO) (ED)
Here, EB=AE= r = the radius of interference fringe & EO= BQ = t = thickness of the film
31
Laboratory Manual of Physics (PY101)

r
t
2
R

t
2
Rt
2
On neglecting t2 in comparison to 2Rt,
t 
Therefore, for bright fringes,
r2
2R

r2 2
1
2
  n
2
R
2
R
n

1

r2
2

or
and for dark fringes,

r nR

When n=0, the radius of dark fringes is zero and the bright fringe is R . Therefore,
alternately dark and bright fringes are produced with dark centre. Suppose the diameter of n th
dark fringe be Dn then,
2
4nR
D

n
and the diameter of (n+p)th ring be Dn+p , then


4
n

p

R
D
2
n

p


4
p

R


D
D
2
2
n

p
n
M- Microscope
G- Glass Plate
L- Convex Lens
P -Plano convex Lens
E – Glass Plate
S - Source

4
p

R
1

D
D
2
2
n

p
n
D D
2
2
np
n
4pR
Here, R is the radius of curvature of Plano convex lens and p is the interval of fringes.
32
Laboratory Manual of Physics (PY101)
Description:
The optical arrangement for Newton’s ring is shown in figure. Light from a
monochromatic source (Sodium lamp) is allowed to fall on convex lens through a broad slit.
Now it falls on a glass plate inclined at an angle 45° to the vertical, thus the parallel beam is
reflected from the lower surface. Due to the air film formed by a glass plate and a Plano
convex lens of large radius of curvature, interference pattern formed which are observed
directly through the traveling microscope. The rings are concentric circles.
Formulae:
D D
1. The wavelength
2
2
n
p
n
4pR
2. Thickness of the air film is
r2
t 
,
2R
where, r = D/2
Observations:
1. The radius of curvature of Plano convex lens = R =115 cm
2. The interval between fringes = p = 5
Observation Table:
For Determination of (Dn+p2-Dn2)
No. of
Rings
Micrometer
Readings
Left end Right end
a cm
b cm
Diameter
D= a-b
cm
30
25
20
15
10
05
00
33
D2
(a-b)2
cm2
(Dn+p2-Dn2)
cm2
Mean
Cm2
t
(cm)
Laboratory Manual of Physics (PY101)
Calculation and Results:
1. The mean wavelength of light from sodium vapor lamp = ……….. Ǻ
Quiz:
1. What is interference? Discuss its types.
2. What is coherent source?
3. What are the conditions for maximum and minimum intensity for the fringes?
4. What is the mechanism for formation of the fringes in this experiment?
5. Show when you will get bands of fringes and circular fringes due to interference?
6. Which type of source is used in the experiment? What will you get if with an
ordinary electric lamp?
7. What will be the change in diameter of the rings if a drop of a transparent liquid
is put between the lens and the plate?
8. What information you can extract from the experiment?
9. Write a brief note on contribution in physics by James Clarke Maxwell.
Date:
Sign of Faculty
34
Laboratory Manual of Physics (PY101)
ULTRASONIC INTERFERROMETER
Aim: Determination of velocity of ultrasonic waves in liquid and its compressibility using
ultrasonic interferometer.
Apparatus: Ultrasonic interferometer (include high frequency generator and measuring
cell) and given liquid.
Formula:
The wavelength of the ultrasonic wave is given by   2d meter.
d→ is the distance moved by the micrometer between successive
Maxima or minima measured in meter.
s1.
 The velocity of the ultrasonic sound waves is given by vf m
f→ is the frequency of the ultrasonic waves in Hz( usually in MHz)
λ→ is the wavelength of the ultrasonic waves in meter.


The compressibility of the given liquid is given by
1 2 1
 2 m
N
v
ρ→ is the density of the given liquied in kgm-3.
for water = 996.45 kgm-3)
v→ is the velocity of the ultrasonic waves in ms-1.
Diagram:
35
Laboratory Manual of Physics (PY101)
Observations:
Least count of the micrometer (LC)=______mm.
TR=PSR+HSR; where HSR= (HSC x LC)
Frequency of the ultrasonic waves f = 2MHz.
Observation Table:
Sr. NO
Micrometer Reading corresponding to
Maximum / Minimum (in mm)
1
2
3
4
5
6
7
8
9
10
36
Difference between Consecutive
maxima / minima ( λ /2)
Laboratory Manual of Physics (PY101)
11
12
13
14
15
16
17
18
19
20
Procedure:








unscrew the knurled cap of cell and lift it away from double walled
construction of the cell. in the middle portion of it pour experimental liquid
and screw the knurled cap. wipe out excess liquid overflowing from the cell.
insert the cell in the heavy base socket and clamp it with the help of a screw
provided on its side.
Connect the high frequency generator to base co-axial cable provided with the
instrument.
keep the "Adj" and "gain" knobs approx at the middle position and adjust
such that current meter needle is approx . at center (50mua A).
Move micrometer slowly either clockwise or anticlockwise direction.
micrometer needle will move either right or to let. Using both knobs, do
adjustment such that the turning point come within the scale. move the
micrometer in the same direction and do adjustment so that other turning
point comes within the scale.
note the readings of micrometer corresponding to the maximum or minimum
(Whichever is Sharper) in micrometer. take about 20 reading of consecutive
maximum or minimum and tabulate them in table.
take average of all differences (λ/2).
once the wavelenth (λ) is known, the velocity (υ) in the liquid can be
calculated with the help of the relation.
υ = λ×f
Result:
(i) The velocity of ultrasound waves is v= f ×λmean =………ms-1
37
Laboratory Manual of Physics (PY101)
 1 
(ii) The compressibility of given liquid   2 =………..m2 N-1.
 v 
Quiz:
1. What are the ultrasonic waves? Discuss their properties.
2. What are the methods for production of ultrasound?
3. How the capitation occurs in liquids by ultrasound? Give its use.
4. Give applications of ultrasound in different fields like medical, mechanical etc.
5. Write brief note on contributions in physics by the organizations like ISRO, PRL.
Date:
Sign of Faculty
38
Laboratory Manual of Physics (PY101)
OPTICAL PROPERTIES OF LIQUID BY LENS
METHOD
Aim: To determine optical properties by lens method
Apparatus: Glass convex lens, parallax pin, plane-mirror, stand, given liquid etc.
Formula:
1
1
1


FC FG FL
Were Fc Focal lent of combination of the liquid and glass lenses. FG= Focal lent of te liquid
and lass convex lens. FL=Focal length of liquid Plano-concave lens.
1 1 
1
 (   1)   
FL
 R1 R2 
Where, μ=Refractive index of the liquid R2 =Radius of curvature of plane surface of the
liquid lens=  . R1= Radius of curvature of concave surface of liquid lens=-R.
Theory:
The refractive index (μ) of a medium is defined as the ratio of the velocity of light in
the vacuum to the velocity of light in that medium. Also for a ray of light in going from a
rarer to a denser medium the ratio of the sine of angle of incidence (i) to the sine of angle of
refractive (r) gives the refractive index of the denser medium with respect to the rarer
medium. If a liquid of refractive index μ be introduced between a convex lens and a plane
mirror a liquid Plano-concave lens if formed between the mirror and the lens. Determination
of the focal length of this combination and focal length of the convex lens enable us to
determine the focal length of the liquid lens from the formula,
1
1
1


FC FG FL
Where FC is the focal length of the combination, FG that of the convex lens and FL that of
liquid lens. From the above relation we get,
FL 
FC FG
FG  FC
Thus knowing R and FL , the refractive index μ of liquid is calculate from te lens-maker
relation.
39
Laboratory Manual of Physics (PY101)
1 1 
1
 (   1)   
FL
 R1 R2 
the radius of the curvature (R2) for the plane surface is  . So from the above relation we get,
1
1
 (   1)  
FL
 R1 
  1
F
R1
 1 G
FL
FL
Procedure:
Arrange the plane mirror, glass convex lens and pin as shown in the figure. Adjust the height
of the pin so that there is no parallax between the pin itself and its image observed in the
convex lens. Measure the height of the pin from center of the lens. This is the focal length
of glass (FG). Place a few drops of liquid on the plane mirror and keep the convex lens over
it. Remove parallax between the pin and its image seen in the common region formed by the
combination of the lenses. This is FC calculate μ.
Observations:
1. FG =_____________ cm.
2. FC =_____________ cm.
3. R2 = 
Calculation:
1. R1= _______cm.
R
2.   1  1  ________ .
FL
Result: The refractive index (μ) of the given liquid is ____________.
40
Laboratory Manual of Physics (PY101)
Quiz:
1. Define focal length of lens.
2. What are nature of real and virtual images?
3. What do you mean by parallax?
4. Define refractive index of a material with respect to vacuum.
5. Why is R1 = - R?
6. What is the function of the plane-mirror?
7. Why is the distance between pin and lens equal to the focal lent when parallax is
removed?
8. What is the unit of μ?
9. What is use of information about the refractive index of the material?
10. Can we perform this experiment using concave lens?
Date:
Sign of Faculty
41