Ses Instruments Pvt. Ltd.

Adarsh Nagar, Roorkee, Uttarakhand

We Offer Four Probe Method It 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. features Easy Resistivity Mapping of Large Sample2-way Movement with Vernier Scales (0.01mm)Spring Loaded Contacts for Firm Connections experiment Consists of the Following: 1. Probes Arrangement, Fpa-01it 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 Tube, Which also Provide Leads for Connections to Constant Current Power Supply and D.c. Microvoltmeter. the Tube Containing Four Probes is Mounted On a Travelling Microscope Type System, Scales and Verniers are Made of Stanless Steels with Following Specification: horizontial: 20 Cm Least Count 0.001 Cmlaterial: 6 Cm Least Count 0.001 Cmvertical: 15 Cm Least Count 0.001 Cm the Bed is of Heavy Casting, Thoroughly Aged and Machined, is Fitted with Leveling Screws. a Large Platform is Provided for Fixing the Sample. 2. Constant Current Source a) Constant Current Source, Model : Ccs-01(for Low Resistivity Samples)the Current Source is Suitable for the Resistivity Measurement of Low to Medium Resistivity Samples such as Thin Films of Metals Alloys and Semiconductors like Germanium. specificationsopen Circuit Voltage: 12vcurrent Range: 0-20ma, 0-200maresolution: 10micro Ampereaccuracy: +-0.25% of the Readingdisplay: 3.5 Digit, 7 Segment Ledload Regulation: +-0.1% for 0 to Full Loadline Regulation: +-0.1% for 10% Changes b) Low Current Source, Model : Lcs-02(for High Resistivity Sample)this Current Source is Especially Suitable for the Resistivity Measurement of Polymer Ceramics and Si Cryustals. specificationsopen Circuit Voltage: 15vcurrent Range: 0-2micro Ampere, 0-20micro Ampere, 0-200micro Ampere & 0-2micro Ampereresolution: Ina At 0-2a Rangeaccuracy: +-0.25% of the Reading 1 Digitdisplay: 3.5 Digit, 7 Segment Lcd with Autopolarityload Regulation: +-0.1% for 0 to Full Loadpower: 3 X 9v Batteries 3. D.c. Microvoltmeter, Dmv-001 the Experiment Complete in all Respects.

We offer Magnetoresistance set-up, 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 = Eyt = v X H 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. The set-up consists of the following: (1) Four Probe arrangement, MRA-01It 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 eliminates 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. (2) SampleGe Crystal (n-type) dimensions: 10x10x0.5mm. (3) Magnetoresistance Set-up, Model DMR-01This 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. (a) Digital MillivoltmeterIntersil 3.5 digit single chip ICL 7107 have been used. Since the use of internal reference causes the degradation in performance due to internal heating an external reference have been used. Digital voltmeter is much more convenient to use, because the input voltage of either polarity can be measured. SpecificationsRange : 0-200mV (100V minimum)Accuracy : +-0.1% of reading +-1 digit (b) Constant Current Power SupplyThis power supply, specially designed for Hall Probe, provides 100% protection against crystal burn-out due to excessive current. The supply is a highly regulated and practically ripple free dc source. SpecificationsCurrent : 0-20mA Resolution : 10micro ampereAccuracy : +-0.2% of the reading +-1 digitLoad regulated : 0.03% for 0 to full loadLine regulation : 0.05% for 10% variation (4) Electromagnet, EMU-50V (5) Constant Current Power Supply, DPS-50 (6) Digital Gaussmeter, DGM-102/DGM-202 The Set-up complete in all respect.

We offer em experiment usefull in physics and material science labs. Our arrangement for measuring em, the charge to mass ratio of the electron is a very simple set-up. It is based on Thomsons method. The em-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 em. This circular path is visible and the diameter d can be measured and em obtained from the relationem = 8V B(2)d(2)This set-up can also be used to study the electron beam deflection for different directions of the magnetic field by varying the orientation of the em-tube. DESCRIPTION OF THE EXPERIMENTAL SET-UP The central part of the set-up is the em-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 magnetic deflection of the beam to be demonstrated. 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. Specifications Helmholtz coils of radii: 14 cmNumber of turns: 160 on each coilAccelerating Voltage: 0 250VDeflection plates voltage: 50V 250VOperating Voltage: 220V AC 50Hz 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 em equal to 1.77x10(11)coul Kg.