Physics And Material Science Lab Experiments

Product Details:

Introduction:

• From the early spectroscopic work it is clear that atoms emitted radiation at discrete frequencies; from Bohr''s model, the frequency of the radiation n is related to the change of energy levels throughDE=hn. It is then to be expected that transfer of energy to atomic electrons by any mechanism should always be in discrete amounts. One such mechanism of energy transfer is through inelastic scattering of low-energy electrons.

Frank and Hertz in 1914 set out to verify these considerations:

• It is possible to excite atoms by low energy electron bombardment.
• The energy trasferred from electrons to the atoms always had discrete values.
• The values so obtained for the energy levels were in agreement with spectroscopic results.
• Thus the existence of atomic energy levels put forward by Bohr can be proved directly. It is a very important experiment and can be performed in any college or University level laboratory.

Operating Principle:

• The Frank-Hertz tube in this instrument is a tetrode filled with the vapour of the experimental substance. Fig.1 indicates the basic scheme of experiment. The electrons emitted by filament can be accelarated by the potential V_G2Kbetween the cathode and the grid GV₂. The grid G₂helps in minimising space charge effects. The grids are wire mesh and allow the electrons to pass through. The plate A is maintained at a potential slightly negative with respect to the grid V₂GV₂. This helps in making the dips in the plate current more prominent. In this experiment, the electron current is measured as a function of the voltage V_G2K. As the voltage increases, the electron energy goes up and so the electron can overcome the retarding potential V_G2Ato reach the plate A. This gives rise to a current in the ammeter, which initially increases. As the voltage further increases, the electron energy reaches the threshold value to excite the atom in its first allowed excited state. In doing so, the electrons loose energy and therefore the number of electrons reaching the plate decreases. This decrease is proportional to the number of inelastic collisions that have occured.When the V_G2Kis increased further and reaches a value twice that of the first excitation potential, it is possible for an electron to excite an atom halfway between the grids, loose all its energy, and then gain anew enough energy to excite a second dip in the current. The advantage of this type of configuration of the potential is that the current dips are much more pronounced, and it is easy to obtain five fold or even larger multiplicity in the excitation of the first level.

Frank-Hertz Experiment Set-up, Model FH-3001, consists of the following:

• Argon filled tetrode
• Filament Power Supply 2.6-3.4V continuously variable
• Power Supply for V_G1K 1.3-5V continuously variable
• Power Supply for V_G2A 1.3 - 12V continuously variable
• Power Supply for V_G2K 0 - 95V continuously variable
• All the power supplies are highly stabilised and output voltages can be read on 31/2 digit, 7 segment LED DPM with autopolarity and decimal indication through a selector switch.
• Saw tooth waveform for CRO display
• Scanning Frequency 115+-20Hz
• Multirange Analogue Voltmeter

Additional Information:

• Item Code: FH3001
• Pay Mode Terms: T/T (Bank Transfer)

Product Details:

Resistivity of Semiconductor by Four Probe Method at different temperatures and determination of the band-gap:

• The Four Probe Method is one of the standard and most widely used method for the measurement of resistivity. In its useful form, the four probes are collinear. The error due to contact resistance, which is significant in the electrical measurement on semiconductors, is avoided by the use of two extra contacts (probes) between the current contacts. In this arrangement the contact resistance may all be high compare to the sample resistance, but as long as the resistance of the sample and contact resistance's are small compared with the effective resistance of the voltage measuring device (potentiometer, electrometer or electronic voltmeter), the measured value will remain unaffected. Because of pressure contacts, the arrangement is also specially useful for quick measurement on different samples or sampling different parts of the sample.

Description of the experimental set-up:

 Probes Arrangement:

• It has four individually spring loaded probes. The probes are collinear and equally spaced. The probes are mounted in a teflon bush, which ensure a good electrical insulation between the probes. A teflon spacer near the tips is also provided to keep the probes at equal distance. The probe arrangement is mounted in a suitable stand, which also hold the sample plate. To ensure the correct measurement of sample temperature, the RTD is enbeded in the sample plate just below the sample. This stand also serves as the lid of temperature controlled oven. Proper leads are provided for the current and voltage measurement.

 Sample:

• Germanium crystal in the form of a chip.

Oven:

• This is high quality temperature controlled oven suitable for Four Probe Set-up. Theoven has been designed for fast heating and cooling rates, which enhances the effectiveness of the controller.

Four Probe Set-up, Dfp-03:

• The set-up consists of three units housed in the same cabinet.

Oven Controller:

• Platinum RTD (A class) has been used for sensing the temperature. A wheatstone bridge and an instrumentation amplifier are used for signal conditioning. Feedback circuit ensures offset and linearity trimming and a fast accurate control of the oven temperature.

 

Multirange Digital Voltmeter:

• In this unit, intersil 31/2 digit single chip A/D Converter ICL 7107 has been used. It has accuracy, auto zero to less than 10 V, zero drift-less than 1 V/ C, input bias current of 10 pA and roll over error of less than one count. Since the use of internal reference causes the degradation in performance due to internal heating, an external reference has been used.

 

Constant Current Generator:

• It is an IC regulated current generator to provide a constant current to the outer probes irrespective of the changing resistance of the sample due to change in temperatures. The basic scheme is to use the feedback principle to limit the load current of the supply to preset maximum value. Variations in the current are achieved by a potentiometer included for that purpose. The supply is a highly regulated and practically ripple freed.c.source. The current is measured by the digital panel meter.
• The experimental set-up is complete in all respect
• Typical results obtained from this set-up are shown in the graph.

Additional Information:

• Pay Mode Terms: T/T (Bank Transfer)

Product Details:

Easy resistivity mapping of large sample 2 - way movement with vernier scales (0.01mm) Spring loaded contacts for firm connections.

Four probe set-up for mapping the resistivity of large samples:

• The Four Probe Method is one of the standard and most widely used method for the measurement of resistivity. In its useful form, the four probes are collinear. The error due to contact resistance, which is significant in the electrical measurement on semiconductors, is avoided by the use of two extra contacts (probes) between the current contacts. In this arrangement the contact resistance may all be high compare to the sample resistance, but as long as the resistance of the sample and contact resistance's are small compared with the effective resistance of the voltage measuring device (potentiometer, electrometer or electronic voltmeter), the measured value will remain unaffected. Because of pressure contacts, and 2 way motion, the arrangement is specially useful for quick measurement on large samples at room temperature.

Additional Information:

• Item Code: FP01
• Pay Mode Terms: T/T (Bank Transfer)

Product Details:

Introduction:

• The resistivity measurements of semiconductors can not reveal whether one or two types of carriers are present; nor distinguish between them. However, this information can be obtained from Hall Coefficient measurements, which are also basic tools for the determination of carrier density and mobilities in conjuction with resistivity measurement.

Theory:

• As you are undoubtedly aware, a static magnetic field has no effect on charges unless they are in motion.When the charges flow, a magnetic field directed perpendicular to the direction of flow produces a mutually perpendicular force on the charges. When this happens, electrons and holes will be separated by opposite forces. They will in turn produce an electric field (E_h) which depends on the cross product of the magnetic intensity, H, and the current density, J. E_h=RJ X H Where R is called the Hall Coefficient Now, let us consider a bar of semiconductor, having dimension, x, y and z. Let J is directed along X and H along Z then E_hwill be along Y. Then we could write Where V_his the Hall voltage appearing between the two surfaces perpendicular to y and I=Jyz.

Hall Effect experiment consists of the following:

• Hall Probe (Ge Crystal) n & p-type
•  Hall Effect Set-up, DHE-21C
• Electromagnet, EMU-50V
• Constant Current Power Supply, DPS-50C
• Digital Gaussmeter, DGM-202C
• Computer Interface, SES-CAMM2

Additional Information:

• Item Code: HEX21C
• Pay Mode Terms: T/T (Bank Transfer)

Product Details:

Measurement of Magnetoresistance in Bismuth:

• It is noticed that the resistance of the sample changes when the magnetic field is turned on. The phenomenon, called magnetoresistance, is due to the fact that the drift velocity of all the carriers is not same. With the magnetic field on; the Hall voltage V = E_yt =|vxH| compensates exactly the Lorentz force for carriers with the average velocity; slower carriers will be over compensated and faster one undercompensated, resulting in trajectories that are not along the applied field. This results in an effective decrease of the mean free path and hence an increase in resistivity.
• Here the above referred symbols are defined as v = drift velocity; E = applied electric field; t = thickness of the crystal; H = Magnetic field

Experimentental Set-Up For Magnetoresistance:

The set-up consists of the following:

• Hall Probe Bismuth
• Constant Current Source, CCS-01
• Digital Microvoltmeter, DMV-001
• Electromagnet, EMU-75(Specifications as per datasheet attached)
• Constant Current Power Supply, DPS-175(Specifications as per datasheet attached)
• Digital Gaussmeter, DGM-102(Specifications as per datasheet attached)

 

Additional Information:

• Item Code: MRB11
• Pay Mode Terms: T/T (Bank Transfer)

Product Details:

Features:

• Suitable for1H and11F nuclei
• FET based marginal Oscillator
• Digital Display of frequency and current
• Clear display of resonance peaks
• Compatible with general purpose CRO

 

Introduction:

• Nuclear Magnetic Resonance (NMR) was discovered by Bloch and Purcell in the year 1945. Over the years it has developed into a very useful and powerful tool in solid state physics, chemistry and biology. In medical application this technique, under the name Magnetic Resonance Imaging (MRI) has been developed as an excellent imaging method for clinical diagnosis. In this method use is made of Zeeman interaction of the magnetic dipoles associated with the nucleus when placed in a external magnetic field.

Elementary Magnetic Resonance:

• An atom whose nucleus has a nulcear spin I will have a magnetic moment as follows= g_nI (1) where _nis nuclear magneton, and g is g-factor. Under the influence of an external static magnetic field (H), these nuclear magnets can orient in distinct directions. Each spin orientation corresponds to a particular energy level given by E = g_nHm_j(2) with mj= -I, -(I-1), ..(I-1), I where mjis magnetic quantum number The splitting of levels will therefore be- DE = g_nH or = hn₀ (3) where n₀is the r.f. frequency applied perpendicular to the static magnetic field. Now if the spins are subjected to a purturbation by an oscillating magnetic field with its direction parallel to the static magnetic field and its frequency n₁such that the quantum hn₁is equal toDE = hn₀, we say that there is a resonance between n₁and n₀. This will induce transition between neighbouring sub levels (m_j=I) and in turn will absorb energy from the oscillating field. Thus, at resonance, we get a peak due to the absorption of energy by the system.

Experimental Technique:

• In our experiment the NMR signals of Hydrogen nuclei and Fluorine nuclei are detected. Both have only two possible orientations in reference to static magnetic field H since both have proton spin I = 1/2. The sample is placed in an r.f.coil located between the gap of homogeneous magnetic field H. In order to exactly match equation (3), H is modulated at constant frequency (50Hz in our case) by using two modulation coils. Each time when the matching (resonance) condition (Eq. 3) is fulfilled, energy is absorbed from the r.f.coil due to the spin transition.

Additional Information:

• Item Code: NMR105
• Pay Mode Terms: T/T (Bank Transfer)

Product Details:

Two Probe Method for resistivity measurement of insulators at different temperatures:

• The Two Probe Method is one of the standard and most commonly used method for the measurement of resistivity of very high resistivity samples like sheets/films of polymers. The resistivity measurement of such samples is beyond the range of Four Probe Method.

Description Of The Experimental Set-Up:

•  Two Probes Arrangement, TPA-01 It has two spring load contact probes. These probes move in a pipe and are insulated by Teflon washers. This probes arrangement is mounted in a suitable stand, which also holds the sample plate and RTD sensor. The stand also serves as the lid of PID Controlled Oven. Teflon coated leads are provided for connecting wit High Voltage Power Supply EHT-11 and Digital Picoammeter DPM-111.
•  PID Controlled Oven, PID-TZ The unit is a high quality PID controller wherein the temperatures can be set and controlled easily. The P, I and D parameters are factory set for immediate use, however, the user may adjust these for specific applications as well as auto-tune the oven whenever required. The steps for these are given in the user manual. Although the controller may be used either for our small oven, up to 200 DegreeC or a larger oven up to 600 DegreeC, however, in the present setup only small oven is to be used. The controller uses thermocouple as temperature sensor.
• High Voltage Power Supply, Model EHT-11 Specifications as per datasheet attached
• Digital Picoammeter, Model DPM-111 Specifications as per datasheet attached. The experimental set-up is complete in all respect

 

Product Details:

Two Probe Method For Resistivity Measurement of Near Insulators at Different Temperatures (Ambient to 600 DC)

Description:

• Behaviour of resistivity of substarte such as polymer sheets/ films at higher temperatures is an important area of investigation due to their variety of applications. Two Probe Method is one of the standard and most commonly used method for the measurement of resistivity of very high resistivity samples like sheets/films of polymers. The resistivity measurement of such samples is beyond the range of Four Probe Method.

Description of the experimental setup:

Two Probes Arrangement:

• It has two individually spring loaded probes. The probes arrangement is mounted in a suitable stand of high quality alumina which also holds the sample plate. To ensure the correct measurement of sample temperature, the thermocouple junction is embedded in the sample plate just below the sample. This stand also serves as the lid of temperature controlled oven. Proper leads are provided for connection to Capacitance Meter and Temperature Controller.

High Temperature Oven:

• This is a high quality temperature controlled oven. The heating element used is a high grade Kanthal- D. It is mounted on a custom made groved, sintered alumina fixture to avoid any slippage of heating wire. Heat shield is also provided to reduce the excessive heating of outer cover. Further the top portion is also suitably covered to meet the safety standard. The oven has been designed for fast heating and cooling rates, which enhances the effectiveness of the controller.

 

PID Temperature Controller:

• It is a high quality PID controller where the temperatures can be set and controlled easily. P, I and D can be adjusted by the user and can also be kept on Auto-tuning.
• High Voltage Power Supply,Model EHT-11
• Digital Picoammeter,Model DPM-111
• The experimental set-up is complete in all respect

Additional Information:

• Item Code: TPX600
• Pay Mode Terms: T/T (Bank Transfer)

Product Details:

Two Probe Method for resistivity measurement of insulators at different temperatures:

• The Two Probe Method is one of the standard and most commonly used method for the measurement of resistivity of very high resistivity samples - near insulators. The resistivity measurement of such samples is beyond the range of Four Probe Method.

Description Of The Experimental Set-Up:

Two Probes Arrangement, TPA-01:

• It has two spring load contact probes. These probes move in a pipe and are insulated by Teflon washers. This probes arrangement is mounted in a suitable stand, which also holds the sample plate and RTD sensor.
• The stand also serves as the lid of PID Controlled Oven. Teflon coated leads are provided for connecting wit High Voltage Power Supply EHT-11C and Digital Picoammeter DPM-111C. With this set-up assuming max. Voltage = 1500V; current 10x10^-12A (max) and thicknexx of sample 1mm, the resistivity of the sample could be measured upto10¹⁴ohm.cm..

PID Controlled Oven, PID-TZ:

• The unit is a high quality PID controller wherein the temperatures can be set and controlled easily. The P, I and D parameters are factory set for immediate use however the user may adjust these for specific applications as well as auto-tune the oven whenever required.
• Please refer to the user manual of the controller for further details. Attachment for connecting computer interface, SES-CAMM is available on the unit.

 
DPM-111C:

• Specification as per item 3, on page 5 - DPM- 111 with extra attachement for connecting computer interface, SES-CAMM.

 EHT-11C:

• Specification as per item 4, on page 5 - EHT-11 with extra attachement for connecting computer interface, SES-CAMM.

Computer Interface, SES-CAMM:

• An interface (SES-CAMM) provides the option to the user to interface it with the computer for acquiring and strong the data (temperature, current and voltage) and plotting in real time. The data is also stored in an excel file which can be used for further analysis. The software is menu driven and can be operated very easily.

Additional Information:

• Item Code: TPX200C
• Pay Mode Terms: T/T (Bank Transfer)

Product Details:

Introduction:

• The electrons in the atoms have discrete stationary states. Franck and Hertz in 1914 describes the first observation of quantized excitation from one quantized state to another one year after N. Bohr published his theory of hydrogen atom. His method depends on detecting the on-set of inelastic collisions between electrons and atoms of the gas under study. The experimental tube in this measurement is essentially a triode filled with the vapour of the experimental substance. The electrons emitted by the heated filament of the tube are accelerated by the positive potential VGK between the cathode and the grid. The grid is a wire mesh which allows the electrons to pass through. The anode A is maintained at a fixed potential VGA slightly negative with respect to the grid. Frank and Hertz in 1914 set out to verify these considerations.

• In the experiment the electron current is measured as a function of the voltage VGK . As VGK increases, the energy of the electrons increases, and more and more electrons reach the anode. The anode current increases. The collisions between the electrons and the atoms are elastic. As VGK further increases, the energy of the electrons reaches the threshold for the excitation of the atomic electrons from the ground state to the first excited state, and the collisions between the electrons and the atoms become inelastic. The colliding electrons lose energy and are not able to overcome the negative potential VGA and the anode current decreases. The potential VGK at the decrease is equal to the first excitation potential of the atom.

Operating Principle:

• In the present ionization potential measurement, the traditional Franck-Hertz set-up as described above has been altered to detect the threshold for ionizing inelastic collisions. The experimental tube is a tetrode filled with argon, the experimental substance. Figure 1 shows the basic circuit diagram. The electrons emitted by the heated filament are accelerated by the potential VG2K between the cathode and the grid G2. The grid G1 helps in minimizing space charge effects. Both the grids consist of wire mesh and allow the electrons to pass through. The anode A is maintained at a potential slightly negative with respect to the cathode. The electrons are never able to reach it. It is ready to receive positive ions if they have been created in the tube. The on-set of anode current therefore signifies the creation of positive ions, i.e. the on-set of ionizing inelastic collisions between the electrons and the argon atoms. In the experiment the electron current is measured as a function of the voltage VG2K . As this voltage increases, the electron energy goes up. But as long as this energy is less than what is required to ionize the atom, the ions are not created, and the anode current remains equal to zero. The inelastic collisions leading to the excitation of argon atoms are immaterial because no ions are created there in and the anode current remains unaffected. The potential VG2K at the on-set of the anode current is equal to the ionization potential. As VG2K further increases, more and more electrons undergo ionizing collisions and the anode current increases. When VG2K reaches a value twice that of the ionization potential, it is possible for an electron to ionize an atom half way between the grid and the cathode, lose all its energy, and then gain anew enough energy to ionize another argon atom. The anode current beginning at this value of VG2K shows a faster increase with VG2K as now there is a larger number of ions reaching the anode.

 

Additional Information:

• Item Code: IP-01
• Pay Mode Terms: T/T (Bank Transfer)

Product Details:

Introduction:

• Our arrangement for measuring e/m, the charge to mass ratio of the electron is a very simple set-up. It is based on Thomson''s method. The e/m-tube is bulb-like and contains a filament, a cathode, a grid, a pair of deflection plates and an anode. The tube is filled with helium at a very low pressure. Some of the electrons emitted by the cathode collide with helium atoms which get excited and radiate visible light. The electron beam thus leaves a visible track in the tube and all manipulations on it can be seen. The tube is placed between a pair of fixed Helmholtz coils which produce a uniform and known magnetic field. The socket of the tube can be rotated so that the electron beam is at right angles to the magnetic field. The beam is deflected in a circular path of radius r depending on the accelerating potential V, the magnetic field B and the charge to mass ratio e/m. This circular path is visible and the diameter d can be measured and e/m obtained from the relation e/m=8V/B²d² This set-up can also be used to study various features of Lorentz force by observing the electron beam deflection for different directions of the magnetic field and different orientations of the e/m-tube.

Description of The Experimental Set Up:

• The central part of the set-up is the e/m-tube. This is energized by
• Filament current supply
• Deflection plates voltage supply
• Continuously variable accelerating voltage supply to the anode.

• The tube is mounted on a rotatable socket and is placed between a pair of Helmholtz coils. The tube can be rotated about a vertical axis, varying the orientation of the electron beam with respect to the Helmholtz coils.This allows deflection of the beam to be demonstrated for various orientations of the beam direction, circular, helical or undeflected paths can be seen. The direction of the current can be changed. The magnetizing current I and the accelerating voltage V are respectively measured by an ammeter and a voltmeter mounted on the front of the panel. The diameter of the electron beam path is measured by a detachable scale mounted in front of the bulb of the tube. This scale has a slider with a hollow tube (fitted with cross wires at its both ends) to fix the line of sight while making the measurements of the beam path diameter. Base of the unit contains the power supply that provides all the required potentials and the current to the Helmholtz coils. The entire apparatus is contained in a wooden case for convenient storage.
• Typical results obtained with the above set-up for variation of the diameter of the electron beam path with the accelerating voltage for a current of 1A to the Helmholtz coils are shown in the following graph. They lead to e/m equal to 1.77 x 10¹¹coul/kg.

Additional Information:

• Item Code: EMX01
• Pay Mode Terms: T/T (Bank Transfer)

Product Details:

Resistivity of Semiconductors by Four Probe Method at Different Temperatures and Determination of the Band-gap

The Four Probe Method is one of the standard and most widely used method for the measurement of resistivity of semiconductors. The experimental arrangement is illustrated. In its useful form, the four probes are collinear. The error due to contact resistance, which is specially serious in the electrical measurement on semiconductors, is avoided by the use of two extra contacts (probes) between the current contacts. In this arrangement the contact resistance may all be high compare to the sample resistance, but as long as the resistance of the sample and contact resistances are small compared with the effective resistance of the voltage measuring device (potentiometer, electrometer or electronic voltmeter),the measured value will remain unaffected. Because of pressure contacts, the arrangement is also specially useful for quick measurement on different samples or sampling different parts of the same sample.

Description of the experimental setup

1. Probes Arrangement
It has four individually spring loaded probes. The probes are collinear and equally spaced. The probes are mounted in a teflon bush, which ensure a good electrical insulation between the probes. A teflon spacer near the tips is also provided to keep the probes at equal distance. The whole -arrangement is mounted on a suitable stand and leads are provided for the voltage measurement.

2. Sample
Germanium crystal in the form of a chip

3. Oven
It is a small oven for the variation of temperature of the crystal from the room temperature to about 200 DegreeC (max.)

4. Four Probe Set-up, DFP-02
The set-up consists of three units in the same cabinet.

(i) Multirange Digital Voltmeter
In this unit, intersil 31/2 digit single chip A/D Converter ICL 7107 has been used. It has high accuracy like auto zero to less than 10mV, zero drift of less than 1mV/ DegreeC, input bias current of 10pA max. and roll-over error of less than one count. Since the use of internal reference causes the degradation in performance due to internal heating, an external reference has been used.

(ii) Constant Current Generator

It is an IC regulated current generator to provide a constant current to the outer probes irrespective of the changing resistance of the sample due to change in temperatures. The basic scheme is to use the feedback principle to limit the load current of the supply to preset maximum value. Variations in the current are achieved by a potentiometer included for that purpose. The supply is a highly regulated and practically ripple free d.c. source. The current is measured by the digital panel meter.

Additional Information:

• Item Code: DFP02
• Pay Mode Terms: T/T (Bank Transfer)

Product Details:

Four Probe Set-Up for Measuring the Resistivity of Very Low to Highly Resistive Samples at Different Temperature

Description:

• The Four Probe Method is one of the standard and most widely used method for the measurement of resistivity. In its useful form, the four probes are collinear. The error due to contact resistance, which is significant in the electrical measurement on semiconductors, is avoided by the use of two extra contacts (probes) between the current contacts. In this arrangement the contact resistance may all be high compare to the sample resistance, but as long as the resistance of the sample and contact resistance''s are small compared with the effective resistance of the voltage measuring device (potentiometer, electrometer or electronic voltmeter), the measured value will remain unaffected. Because of pressure contacts, the arrangement is also specially useful for quick measurement on different samples or sampling different parts of the sample.

Description Of The Experimental Set-Up:

• Probes Arrangement
•  PID Controlled Oven, Model PID-TZ
• Constant Current Source
•  Constant Current Source, ModelCCS-01
•  Low Current Source, Model LCS-02
• (for high resistivity samples)
•  D.C. Microvoltmeter

Additional Information:

• Item Code: DFP-RM-200
• Pay Mode Terms: T/T (Bank Transfer)

Product Details:

It is noticed that the resistance of the sample changes when the magnetic field is turned on. The phenomenon, called magnetoresistance, is due to the fact that the drift velocity of all carriers is not same. With the magnetic field on; the Hall voltage V is given as which compensates exactly the Lorentz force for carriers with the average velocity; slower carriers will be over compensated and faster one undercompensated, resulting in trajectories that are not along the applied field. This results in an effective decrease of the mean free path and hence an increase in resistivity.

Here the above referred symbols are defines as v = drift velocity; E = applied electric field; t = thickness of the crystal; H = Magnetic field

Description of the experimental setup:

•  Four probe arrangement
• Sample (Ge p-type)
• Magnetoresistance set-up,
  Model DMR-11
• Electromagnet, Model EMU-50V
• Constant Current Power Supply,
  Model DPS-50
• Digital Gaussmeter, Model DGM-102

Four Probe arrangement:

• It consists of 4 collinear, equally spaced (2mm) and individually spring loaded probes mounted on a PCB strip. Two outer probes for supplying the constant current to the sample and two inner probes for measuring the voltage developed across these probes. This eliminate the error due to contact resistance which is particularly serious in semiconductors. A platform is also provided for placing the sample and mounting the Four Probes on it.

Magnetoresistance Set-up, Model DMR-11:

• This unit consists of a digital millivoltmeter and constant current power supply. The voltage and probe current can be read on the same digital panel meter through a selector switch.

 

 

Additional Information:

• Item Code: MRX01
• Pay Mode Terms: T/T (Bank Transfer)

Product Details:

Two Probe Method For Resistivity Measurement of Near Insulators at Different Temperatures (Ambient to 600 DegreeC) with computer interfacing facility:

Description:

• Behaviour of resistivity of substarte such as polymer sheets/ films at higher temperatures is an important area of investigation due to their variety of applications. Two Probe Method is one of the standard and most commonly used method for the measurement of resistivity of very high resistivity samples like sheets/films of polymers. The resistivity measurement of such samples is beyond the range of Four Probe Method.

 

Description Of The Experimental Set-Up:

• Two Probes Arrangement
• High Temperature Oven
• PID Temperature Controller
• High Voltage Power Supply, Model EHT-11C
• Digital Picoammeter, Model DPM-111C
• Computer Interface, SES-CAMM

Additional Information:

• Item Code: TPX600C
• Pay Mode Terms: T/T (Bank Transfer)

Product Details:

Study of Thermoluminescence of F-centers in Alkali Halide Crystals:

• Pure alkali halide crystals are transparent throughout the visible region of the spectrum. The crystals may be colored in a number of ways
• by the introduction of chemical impurities
•  by introducing an excess of the metal ion
•  by X-ray,g-ray, neutron and electron bombardment
•  by electrolysis

A colour centre is a lattice defect that absorbs visible light. The simplest colour center is an F-centre. The name comes from the German word for colour, Forbs. We usually produce F-centres by heating the crystal in excess alkali vapours or by irradiation. The new crystals show an absorption band in the visible or ultraviolet, whereas the original crystals are transparent in that region. This absorption band is called F-band.

An F-centre can be regarded as a negative ion vacancy and an electron which is equally shared by the positive ions, surrounding the vacant lattice site. Conversely a hole may be trapped at a +ve ion vacancy or at a -ve ion, giving rise to V- and H-centres respectively.

Color centres produced by irradiation with x-rays:

• When a X-ray quantum passes through an ionic crystal, it will usually give rise to a fast photo-electron with an energy of the same order as that of the incident quantum. Such electrons, because of their small mass, do not have sufficient momentum to displace ions and therefore loose their energy in producing free electrons, holes, excitons and phonons. Evidently these while moving near the vacancies form trapped electrons as well as trapped holes.
• The trapped-electron or trapped-hole centres so formed can be destroyed (bleached) by illuminating the crystal with light of the appropriate wavelength or warming it.

Thermoluminescence:

• Important information about the colour centres can be obtained by measuring the changes that occur when a coloured crystal is gradually heated. As the temperature is raised electrons and holes escape from their traps at an increasing rate. The freed charges can recombine with each other or with other defects and give out luminescence by recombination. The resulting thermoluminescence or ''glow'' reaches maximum and then decreases to zero as the supply of trapped electrons or holes becomes exhausted. The plot of luminescence intensity verses temperature, taken at a constant heating rate, is called the ''glow curve''. It may contain one or many glow peaks, depending upon whether there are one or several different kinds of traps.
• From the glow curve one determine the trap depth; the deeper the trap, the higher the temperature of the glow peak. A correlation between the temperature at which thermoluminescence occurs and the temperature at which particular band bleach can give valuable information about specific centres.

The experiment consists of the following:

 Experimental Set-Up for creating Thermolumnescece:

• Sample KBr or KCl single crystal
• Thermolumniscence Temperature Meter, TL-02
• Digital Thermometer with RTD sensor
• Oven Power Supply
• Sample Holder
• Thermolumniscence Oven (upto 423K)
• Black Box

For Measurement of Luminescence Intensity:

• Photomultiplier tube 931A
• PMT Housing with biasing circuit and coaxial cables etc.
• High Voltage Power Supply, Model EHT-11
• Nanoammeter, Model DNM-121

 

Additional Information:

• Item Code: TLX02
• Pay Mode Terms: T/T (Bank Transfer)

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Introduction:

• When a current-carrying conductor is placed in a magnetic field perpendicular to the current direction, a voltage develops transverse to the cuurent. This voltage was first observed in 1879 by Edwin Hall and the effect is called Hall Effect.
• The Hall effect has since led to a deeper understanding of the details of the conduction process. It can yield the density of the charge carriers as well as their sign.

Theory:

As you are aware, a static magnetic field has no effect on charges unless they are in motion. When the charges flow, a magnetic field directed perpendicular to the direction of flow produces a mutually perpendicular force on the charges. When this happens, electrons and holes will be separated by opposite forces. They will in turn produce an electric field ( E_h) which depends on the cross product of the magnetic intensity, H , and the current density, J.E_h=RJ X H where R is called the Hall Coefficient Now, let us consider a bar of a semiconductor, having dimensions, x, y and z. Let J be directed along X and H along Z, then E_hwill be along Y. Then we could write where V_his the Hall voltage appearing between the two surfaces perpendicular to y and I=Jyz.

Hall Effect experiment consists of the following:

• Hall Probe Bismuth
•  Constant Current Source, CCS-01
• Digital Microvoltmeter, DMV-001
• Electromagnet, EMU-75(Specifications as per datasheet attached)
• Constant Current Power Supply, DPS-175(Specifications as per datasheet attached)
• Digital Gaussmeter, DGM-102(Specifications as per datasheet attached)

Additional Information:

• Item Code: HEB11
• Pay Mode Terms: T/T (Bank Transfer)

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HEM 01 Hall Effect In Metals enables the charge carrier concentration and mobility to be determined by experiment. Direction of the Hall Voltage in silver indicates negative charge carriers, which is in agreement with concepts of the model of the ''free electron gas''. Limitations of this model are shown by the so called ''abnormal Hall Effect'' of tungsten. The experiment carried out under identical conditions for tungsten show the Hall Voltage to have about same magnitude but opposite direction as in silver. This can be explained by the ''Energy Band diagram''. The tungsten atom has .5s²5p⁶5d⁴6s²electronic structure. When the atoms come close together to form the solid, the close lying states 5d and 6s broaden into bands, with s band broadening considerably more than the d band. This is because of the larger size of the s orbital. The figure schema- tically shows the allowed energies as a function of the interatomic distance. The number of allowed states is ten per atom in the d band and two in the s band. In tungsten there are six electrons to be shared between these two bands. The result is that at the interatomic distance in tungsten there are holes in the d band and electrons in the s band, making tungsten predominantly a hole conductor. This sort of mixed (electrons and holes) conduction is a general characteristic of transition metals. The apparatus consists of the following

Description of the experimental set-up:

The set-up consists of the following:

•  Hall Probe-Silver (HP-Ag)
•  Hall Probe-Tungsten (HP-W)
•  High Current Power Supply, Model PS-20A
•  Digital Microvoltmeter,DMV-001
•  Electromagnet,EMU-75T
•  Constant Current Power Supply,DPS-175
•  Gaussmeter,DGM-202 or DGM-102

 

Additional Information:

• Item Code: HEM01
• Pay Mode Terms: T/T (Bank Transfer)

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Introduction:

• The Zeeman effect is the splitting of spectral lines of atoms when they are placed in a magnetic field. It exhibits space quantization and is one of the few fundamental atomic physics experiments which can be performed in a teaching laboratory.

Description of the experimental setup Experimentental Set-up for Zeeman Experiment: 

The set-up consists of the following:

•  High Resolution Fabry Perot Etalon, FP-01
•  Mercury Discharge Tube, MT-01 (Low Pressure Mercury Discharge Tube)
•  Power Supply for MT-01, MTPS-01 (H.V. Power Supply for Discharge Tube)
•  Narrow Band Interference Filter, IF-01
•  Polarizer with lens, PL-01
•  Optical Bench OB-01
•  CCD Camera CCD-01 (High Resolution CCD Camera)
•  Telescope with Focussing Lens FL-01
•  Monitor 14" TV-14
•  Electromagnet, EMU-50T
•  Constant Current Power Supply, DPS-50
•  Digital Gaussmeter, DGM-102

Result:

• The interference pattern is in the form of circular rings. These are split when the magnetic field is switched on. The amount of splitting depends on the external magnetic field, charge to mass ratio of electron and Lande''s g-factors of the electronic energy levels involved in the transition. These later quantities can be obtained from this experiment.
• The result of this unit are within 5% of the standard value.

Additional Information:

• Item Code: ZEX01
• Pay Mode Terms: T/T (Bank Transfer)

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Determination of Planck''s Constant and Work Function of Materials by Photoelectric Effect:

• It was observed as early as 1905 that most metals under influence of radiation, emit electrons. This phenomenon was termed as photoelectric emission. The detailed study of it has shown.
• That the emission process depends strongly on frequency of radiation.
• For each metal there exists a critical frequency such that light of lower frequency is unable to liberate electrons, while light of higher frequency always does.
• The emission of electron occurs within a very short time interval after arrival of the radiation and member of electrons is strictly proportional to the intensity of this radiation.
• The experimental facts given above are among the strongest evidence that the electromagnetic field is quantified and the field consists of quanta of energy E= hnwherenis the frequency of the radiation and h is the Planck''s constant. These quanta are called photons.
• Further it is assumed that electrons are bound inside the metal surface with an energy ef, where f is called work function. It then follows that if the frequency of the light is such that hn> ef it will be possible to eject photoelectron, while if hn< ef, it would be impossible. In the former case, the excess energy of quantum appears as kinetic energy of the electron, so that hn= 1/2(mn²+ ef). Which is the famous photoelectrons equation formulated by Einstein in 1905. The energy of emitted photoelectrons can be measured by simple retarding potential techniques as is done in this experiment. When a retarding potential V₀is used to measure kinetic energy of electrons E_e, we have, E_e= 1/2(mv²) = eV₀ or V₀= (h/e)(n-f). So when we plot a graph V₀as a function ofn, the slope of the straight line yields h and the intercept of extrapolated pointn=0 can give work functionf.

The Apparatus Consist Of The Following:

•  Photo Sensitive Device Vacuum photo tube.
• Light source Halogen tungsten lamp 12V/35W.
• Colour Filters 635nm, 570nm, 540nm, 500nm & 460nm.
•  Accelerating Voltage Regulated Voltage Power Supply, It is high stability low current measuring instrument
•  Current Detecting Unit Digital Nanoammeter
• Optical Bench The light source can be moved along it to adjust the distance between light source and phototube scale length is 400 mm. A drawtube is provided to install colour filter, a focus lense is fixed in the back end.
•  Power Requirement 220V +- 10%, 50Hz.

 

Additional Information:

• Item Code: PC101
• Pay Mode Terms: T/T (Bank Transfer)

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Other Detail:

• Highly accurate results
• Precise measurement of Band-Gap
• Clear physical interpretation
• Self contained unit with no extra accessory required

Introduction:

• Several proposals to measure the Planck''s Constant for didactical purposes, using the current - voltage (I-V) characteristics of a light emitting diode (LED) have been made quite regularly in the last few years. The reason is that the experiment can be done easily in any lab and the result are surprisingly good (+-10%). The physical interpretation however is not completely clear and this has raised many discussions, which has been published almost with same regularity as the proposals themselves.
• The present experiment is based on diode current for Vo, using the diode law. I = I_oexp [- e (V_o- V)/hkT] where, e is electronic charge, k is Boltzmann constant, T is absolute temperature and h is material constant which depends on the type of diode, the location of recombination region, etc.
• The correct method to determine the real height of the potential energy barrier Vo is to directly measure the dependence of the current on temperature keeping the applied voltage V slightly below Vo. The idea is that the disturbance to Vo is as little as possible. The slope of ln I vs. 1/T curve gives e (V_o- V)hk (Fig. 1). The constant h is determined from I-V characteristics of the diode (Fig. 2) at room temperature from the relation h= (e/kt) (DV/Dln I) Compared with previous methods, this determination of Vo is more precise and more accurate and at the same time the physical interpretation is more transparent. The Planck''s constant is then obtained by the relation h= e V_ol/c. The wavelength (l) of the light emitted by the diode can be measured by a transmission grating spectrometer normally available in the lab.
• The value of Plank''s constant obtained from this method is within 5% of accepted value (6.62 x 10^-34Joules.sec).

• It is a self contained unit. All the necessary facilities and measuring devices are built in a single unit, as a result only minimum of external connections need to be made.

Dependence of current (I) on temperature (T) at constant applied voltage (V):

The following facilities are built in for this

Material Constanth:

• To draw I-V characteristics of LED for determination ofh, a variable voltage source and current meter are provided with 31/2 digit display.

Additional Information:

• Item Code: PCA-01
• Pay Mode Terms: T/T (Bank Transfer)

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Introduction:

• This experiment aims at measuring the charge of an electron and is perhaps the most basic of all atomic physics or modern physics laboratory experiments. It won Millikan the Nobal Prize in the year 1923. The experiment depends on the ability to control, measure and balance very small force of the order 10^-14N. The set-up consists of two horizontal parallel plates separated by about 5mm. The upper plate has a small hole through which microscopic oil droplets are sprayed in between the two plates with the help of an atomizer which is like a common perfume sprayer. These droplets get charged due to the frictional force during spraying. The free fall of these droplets in the space between the plates is observed in the gravitational field. A measurement of the velocity of fall along with the use of Stokes law leads to the calculation of the mass of the droplets and their radii if the oil density is known. These are of the order of 10^-15kg and 10^-6m respectively. By applying a potential difference between the plates, a uniform electric field is produced in the space between the plates. A measurement of the velocity of the negatively charged droplets rising in the electric field allows a calculation of the electric force on the droplets and hence the charge carried by them. In the experiment the droplets which rise and fall slowly are selected as they are expected to have a fairly small charge. These droplets are made to rise and fall several times. The repetitions of measurement of the velocities of rise and fall reduce the random error of their means. A fairly large number of droplets are observed and their charges are calculated. The analysis of the data on the total charge carried by the droplets shows that these total charges are integral multiples of a certain smallest charge which is the charge of an electron. This result also shows that the charge is quantized.

• The measurement of the charge on the electron can lead to the calculation of Avogadro''s number. The charge F (the Faraday) required to electro-deposit one gram equivalent of an element on an electrode during electrolysis is equal to the charge of the electron multiplied by the number of molecules in a mole. The Faraday has been found to be F = 9.625 10⁷coulombs per kilogram equivalent weight. Hence Avogadro''s number N = F/e

Additional Information:

• Item Code: MOD01
• Pay Mode Terms: T/T (Bank Transfer)

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Features:

• FET based marginal R.F. Oscillator
• Digital diaplay of frequency
• Excellent peaks display
• Digital display of Helmoltz Coil Current
• Compatible with general pupose CRO in X-Y mode

 

Introduction:

• In recent years Magnetic Resonance has developed into a very useful and powerful tool in solid state research. In this method, use is made of the Zeeman interaction of the magnetic dipoles associated with the nucleus or electron, when placed in an external magnetic field. Accordingly, they are identified as NMR (Nuclear Magnetic Resonance) or ESR (Electron Spin Resonance). This form of spectroscopy finds many applications in the investigation of crystal structures, environmental effects, dynamic effects, defects in solids and in many diverse branches of Physics, Chemistry and Biology.

Elementary Magnetic Resonance:

• We know that the intrinsic angular momentum (spin) of the electron S couples with the orbital angular momentum of the electronto give a resultantand this coupling gives rise to the ''fine structure'' of the spectra. Further, under the influence of an external magnetic field (H) each of the level will split into (2j+1) sublevels (Zeeman effect) and the splitting of a level will be DE = (g₀H)m_j where ₀is the Bhor magneton, g is the Lande'' g-factor and mj is the magnetic quantum number. As can be seen, the splitting is not same for all levels; it depends on theandof the level (s=1/2 always for one electron). However, the sublevels will split equally by an amount DE = g₀H or = hn₀ wheren₀is the frequency of the system. Now if the electron is subjected to a perturbation by an oscillating magnetic field with its direction perpendicular to the static magnetic field and its frequencyn₁such that the quantumn1 is equal to E=hn₀, we say that there is a resonance between n1 andn₀. This willinduce transition between neighbouring sublevels (mj=+-1) and in turn will absorb energy from oscillating field. Thus, at resonance, we get a peak due to the absorption of energy by the system

Experimental Technique:

• If we consider a free electron and substitute the proper value of constants in the equation g=2.00, ₀=0.927X10-20 erg/gauss & h=6.625 X l0^-27erg sec, we get. That is ESR can be observed at radio frequencies in a magnetic field of a few gauss or in the microwave region in a magnetic field of a few kilogauss. The latter alternate has many advantages improved signal-to-noise ratio, high resolution etc. and is always preferred for accurate work, though it is very sophisticated and expensive. However, if the basic understanding of the subject is the main criteria as is usually the requirement of class room experiments, the observation of ESR in low magnetic field and in a radio frequency region makes it a lot simple, inexpensive and within the reach of every post-graduate laboratory.

Additional Information:

• Item Code: ESR105
• Pay Mode Terms: T/T (Bank Transfer)

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Introduction:

• The resistivity measurements of semiconductors can not reveal whether one or two types of carriers are present; nor distinguish between them. However, this information can be obtained from Hall Coefficient measurements, which are also basic tools for the determination of carrier density and mobilities in conjuction with resistivity measurement.

Theory:

• As you are undoubtedly aware, a static magnetic field has no effect on charges unless they are in motion. When the charges flow, a magnetic field directed perpendicular to the direction of flow produces a mutually perpendicular force on the charges. When this happens, electrons and holes will be separated by opposite forces. They will in turn produce an electric field (_h) which depends on the cross product of the magnetic intensity,, and the current density, J. _h= Rx Where R is called the Hall coefficient. Now, let us consider a bar of semiconductor, having dimension, x, y and z. Letis directed along X andalong Z then_hwill be along Y, as in Fig. 2. Then we could write. Where Vh is the Hall voltage appearing between the two surfaces perpendicular to y and I =yz

Hall Effect experiment consists of the following: 

• Hall Probe (Ge Crystal);(b)Hall Probe (InAs)
• Hall Effect Set-up (Digital), DHE-21
•  Electromagnet,EMU-75orEMU-50V
• Constant Current Power Supply, DPS-175 or DPS-50
• Digital Gaussmeter, DGM-102

Additional Information:

• Item Code: HEX21
• Pay Mode Terms: T/T (Bank Transfer)